Diskless Nodes HOW-TO document for Linux Robert Nemkin buci@math.klte.hu , Al Dev (Alavoor Vasudevan) - Maintainer of this HOWTO alavoor@yahoo.com , Markus Gutschke markus+etherboot@gutschke.com , Ken Yap ken.yap@acm.org , Zurück zu Gero gero@gkminix.han.de v1.0, 13 May 1999 This document describes how to set up a diskless Linux box. As tech­ nology is advancing rapidly, networkcards are becoming cheaper and much faster - 100 MBits ethernet is standard now and in about 1 to 2 years 1000 MBits i.e. 1GigBits ethernet cards will become a industry standard. With high-speed network cards, remote access will become as fast as the local disk access which will make diskless nodes a viable alternative to workstations in local LAN. Also diskless nodes elimi­ nates the cost of software upgrades and system administration costs like backup, recovery which will be centralized on the server side. Diskless nodes also enable "sharing/optimization" of centralised server CPU, memory, hard-disk, tape and cdrom resources. Diskless nodes provides mobility for the users i.e., users can log on from any one of diskless nodes and are not tied to one workstation. Diskless Linux box completely eliminates the need for local floppy disk, cdrom drive, tape drive and hard-disk. Diskless nodes JUST has a network card, 8MB RAM, a low-end cpu and a very simple mother-board which does not have any interface sockets/slots for harddisks, modem, cdrom, floppy etc.. With Diskless linux nodes you can run programs on remote Linux 64 CPU SMP box or even on Linux super-computer! Diskless nodes lowers the "Total Cost of Ownership" of the computer system. This document is copy­righted by Robert Nemkin and other authors as listed above. Copyright policy is GPL. Thanks to Bela Kis bkis@car­ tan.math.klte.hu for translating this initial document v0.0.3 (which was a mini-howto) to English. ______________________________________________________________________ Table of Contents 1. Other Formats of this Document 2. Introduction to Network Booting and Etherboot 2.1 What is Network booting? 2.2 How does it work 2.3 Netbooting in Practice 2.4 Uses of Network booting 2.5 For more information 3. Begin setup 3.1 Document Changes 3.2 How to set up a diskless Linux box 3.3 Related documents 3.4 How does it work? 3.5 Hardware 4. Fundamental ideas 4.1 Setting up the PC 4.2 Setting up a bootpd on the server 4.3 Configure the bootpd on the server 4.4 Understanding tftp 4.5 Kernel Image 4.6 Setting up a minimal Linux configuration on the remote server 4.7 Configuring the tftp server 4.8 Final work 4.9 Net Loader 4.10 RH5 configuration 4.11 Gotchas and caveats 4.12 X-terminal 5. Trouble shooting 5.1 Memory and diskspace requirements; speed 5.2 Possible errors 5.3 Errors and possible further expansions of this document 6. EEPROM Burners and Memory chips 6.1 List of EEPROM Burner manufacturers 6.2 Non-Volatile Memory chips 7. Etherboot 7.1 Introduction 7.1.1 What hardware is supported? 7.1.2 Availability of this document 7.1.3 Getting help 7.2 Unpacking, compiling and testing the package 7.2.1 Unpacking the distribution 7.2.2 Compiling the ROM images 7.2.3 Testing the ROM images 7.3 Setting up a diskless boot 7.3.1 Making a tagged image 7.3.2 Compiling a custom kernel 7.3.3 Setting up a bootp daemon 7.3.4 Setting up a DHCP daemon 7.3.5 Setting up a tftp daemon 7.4 Testing the network booting 7.4.1 Setting up a NFS root filesystem 7.4.2 Swap over NFS 7.5 Booting DOS 7.6 Making an Etherboot EPROM or EEPROM 7.6.1 Choosing the EPROM 7.6.2 Enabling the EPROM 7.6.3 Size and speed of the EPROM 7.7 Troubleshooting tips 7.8 Acknowledgements 7.9 Copyright 8. Netboot 8.1 Introduction 8.2 README 8.2.1 Copyright Notice, Acknowledgements 8.2.2 Overview 8.2.3 Features 8.2.4 Installation 8.2.5 Mailing list 8.2.6 Disclaimer 8.3 Download Netboot 8.4 Netboot useful links 8.5 RFC 951 8.6 RFC 1533 8.7 RFC 1350 8.8 Install Instructions 8.9 Troubleshoot Problems ______________________________________________________________________ 1. Other Formats of this Document This document is published in 10 different formats namely - DVI, Postscript, Latex, LyX, GNU-info, HTML, RTF(Rich Text Format), Plain- text, Unix man pages and SGML. · You can get this HOWTO document as a single file tar ball in HTML, DVI, Postscript or SGML formats from - · Plain text format is in: · Translations to other languages like French, German, Spanish, Chinese, Japanese are in Any help from you to translate to other languages is welcome. The document is written using a tool called "SGML tool" which can be got from - Compiling the source you will get the following commands like · sgml2html databasehowto.sgml (to generate html file) · sgml2rtf databasehowto.sgml (to generate RTF file) · sgml2latex databasehowto.sgml (to generate latex file) This document is located at - · Also you can find this document at the following mirrors sites - · · · · · Other mirror sites near you (network-address-wise) can be found at select a site and go to directory /LDP/HOWTO/Diskless-HOWTO.html In order to view the document in dvi format, use the xdvi program. The xdvi program is located in tetex-xdvi*.rpm package in Redhat Linux which can be located through ControlPanel | Applications | Publishing | TeX menu buttons. To read dvi document give the command - xdvi -geometry 80x90 howto.dvi And resize the window with mouse. See man page on xdvi. To navigate use Arrow keys, Page Up, Page Down keys, also you can use 'f', 'd', 'u', 'c', 'l', 'r', 'p', 'n' letter keys to move up, down, center, next page, previous page etc. To turn off expert menu press 'x'. You can read postscript file using the program 'gv' (ghostview) or The ghostscript program is in ghostscript*.rpm package and gv program is in gv*.rpm package in Redhat Linux which can be located through Con­ trolPanel | Applications | Graphics menu buttons. The gv program is much more user friendly than ghostscript. Also ghostscript and gv are available on other platforms like OS/2, Windows 95 and NT, you view this document even on those platforms. To read postscript document give the command - gv howto.ps To use ghostscript give - ghostscript howto.ps 2. Introduction to Network Booting and Etherboot This chapter is written by Ken Yap and explains how to bootstrap your computer from a program stored in non-volatile memory without accessing your hard disk. It is an ideal technique for maintaining and configure a farm of linux boxes 2.1. What is Network booting? Network booting is an old idea. The central idea is that the computer has some bootstrap code in non-volatile memory, e.g. a ROM chip, that will allow it to contact a server and obtain system files over a network link. One goal is to avoid the use of a hard disk for booting. There are various reasons for doing this. One is to reduce the cost of maintaining software on many different machines. With network booting the files are held at a central server and can be updated at one location. Another goal is to use computers in locations where hard disks are not robust enough. For example this might be a computer on a factory floor where a hard disk might be too fragile. Finally another goal is to have a system that can be switched between different operating systems without having to reload the software. Network booting often co-exists with disk booting. For example, a system could run Windows from disk but sometimes boot Linux from the network. There are some interesting applications of this technique. For example: a friend of mine uses this to reload Windows over the network. When a Windows installation becomes corrupted, as it often does, the sysadmin can reload a fresh installation by booting Linux over the network and letting the automatic script format the disk and copy a fresh Windows installation onto it. 2.2. How does it work In order to boot over the network, the computer must get 1. an identity, 2. an operating system image and 3. usually, a working filesystem. Consider a diskless computer (DC) that has a network boot ROM. It may be one of several identical DCs. How can we distinguish this computer from others? There is one piece of information that is unique to that computer (actually its network adapter) and that is its Ethernet address. Every Ethernet adapter in the world has a unique 48 bit Ethernet address because every Ethernet hardware manufacturer has been assigned blocks of addresses. By convention these addresses are written as hex digits with colons separating each group of two digits, for example: 00:60:08:C7:A3:D8. The protocols used for obtaining an IP address, given an Ethernet address, are called Boot Protocol (BOOTP) and Dynamic Host Configuration Protocol (DHCP). DHCP is an evolution of BOOTP. In our discussion, unless otherwise stated, anything that applies to BOOTP also applies to DHCP. (Actually it's a small lie that BOOTP and DHCP only translate Ethernet addresses. In their foresight, the designers made provision for BOOTP and DHCP to work with any kind of hardware address. But Ethernet is what most people will be using.) An example of a BOOTP exchange goes like this: DC: Hello, my hardware address is 00:60:08:C7:A3:D8, please give me my IP address. BOOTP server: (Looks up address in database.) Your name is aldebaran, your IP address is 192.168.1.100, your server is 192.168.1.1, the file you are supposed to boot from is /tftpboot/vmlinux.nb (and a few other pieces of information). You may wonder how the DC found the address of the BOOTP server in the first place. The answer is that it didn't. The BOOTP request was broadcast on the local network and any BOOTP server that can answer the request will. After obtaining an IP address, the DC must download an operating system image and execute it. Another Internet protocol is used here, called Trivial File Transfer Protocol (TFTP). TFTP is like a cut-down version of FTP---there is no authentication, and it runs over User Datagram Protocol (UDP) instead of Transmission Control Protocol (TCP). UDP was chosen instead of TCP for simplicity. The implementation of UDP on the DC can be small so the code is easy to fit on a ROM. Because UDP is a block oriented, as opposed to a stream oriented, protocol, the transfer goes block by block, like this: DC: Give me block 1 of /tftpboot/vmlinux.nb. TFTP server: Here it is. DC: Give me block 2. and so on, until the whole file is transferred. Handshaking is a simple acknowledge each block scheme, and packet loss is handled by retransmit on timeout. When all blocks have been received, the network boot ROM hands control to the operating system image at the entry point. Finally, in order to run an operating system, a root filesystem must be provided. The protocol used by Linux and other Unixes is normally Network File System (NFS), although other choices are possible. In this case the code does not have to reside in the ROM but can be part of the operating system we just downloaded. However the operating system must be capable of running with a root filesystem that is a NFS, instead of a real disk. Linux has the required configuration variables to build a version that can do so. 2.3. Netbooting in Practice Besides commercial boot ROMs, there are two sources for free packages for network booting. They are Etherboot and Netboot. Both can be found through the Etherboot home page. First you have to ascertain that your network card is supported by Etherboot or Netboot. Eventually you have to find a person who is willing to put the code on an EPROM (Erasable Programmable Read Only Memory) for you but in the beginning you can do network booting from a floppy. To create a boot floppy, a special boot block is provided in the distribution. This small 512 byte program loads the disk blocks following it on the floppy into memory and starts execution. Thus to make a boot floppy, one has only to concatenate the boot block with the Etherboot binary containing the driver for one's network card like this: cat floppyload.bin 3c509.lzrom > /dev/fd0 Before you put in the network boot floppy, you have to set up three services on Linux: BOOTP (or DHCP), TFTP and NFS. You don't have to set up all three at once, you can do them step by step, making sure each step works before going on to the next. I assume you have installed the bootpd server from a distribution or by compiling from source. You then have to ensure that this server is waiting for bootp requests. There are two ways to do this: one is to start bootpd as a network service that is always listening when the computer is up, and the other is to start it from inetd. For the latter, /etc/inetd.conf should contain a line like this: bootps dgram udp wait root /usr/sbin/tcpd bootpd If you had to modify /etc/inetd.conf, then you need to restart inetd by sending the process a HUP signal. Next, you need to give bootp a database to map Ethernet addresses to IP addresses. This database is in /etc/bootptab. It contains lines of the following form: aldebaran.foo.com:ha=006008C7A3D8:ip=192.168.1.100:bf=/tftpboot/vmlinuz.nb Other information can be specified but we will start simple. Now boot the DC with the floppy and it should detect your Ethernet card and broadcast a BOOTP request. If all goes well, the server should respond to the DC with the information required. Since /tftpboot/vmlinux.nb doesn't exist yet, it will fail when it tries to load the file. Now you need to compile a special kernel, one that has the option for mounting the root filesystem from NFS turned on. You also need to enable the option to get the IP address of the kernel from the original BOOTP reply. You also need to compile the Linux driver for your network adapter into the kernel instead of loading it as a module. It is possible to download an initial ramdisk so that module loading works but this is something you can do later. You cannot install the zImage resulting from the kernel compilation directly. It has to be turned into a tagged image. A tagged image is a normal kernel image with a special header that tells the network bootloader where the bytes go in memory and at what address to start the program. You use a program called mknbi-linux to create this tagged image. This utility can be found in the Etherboot distribution. After you have generated the image, put it in the /tftpboot directory under the name specified in /etc/bootptab. Make sure to make this file world readable because the tftp server does not have special privileges. For TFTP, I assume that you installed tftpd from a distribution or by compiling from source. Tftpd is normally started up from inetd with a line like this in /etc/inetd.conf. tftp dgram udp wait root /usr/sbin/tcpd in.tftpd -s /tftpboot Again, restart inetd with a HUP signal and you can retry the boot and this time it should download the kernel image and start it. You will find that the boot will continue until the point where it tries to mount a root filesystem. At this point you must configure and export NFS partitions to proceed. For various reasons, it's not a good idea to use the root filesystem of the server as the root filesystem of the DCs. One is simply that there are various configuration files there and the DC will get the wrong information that way. Another is security. It's dangerous to allow write access (and write access is needed for the root filesystem, for various reasons) to your server's root. However the good news is that a root filesystem for the DC is not very large, only about 30 MB and a lot of this can be shared between multiple DCs. Ideally, to construct a root filesystem, you have to know what files your operating system distribution is expecting to see there. Critical to booting are device files, files in /sbin and /etc. You can bypass a lot of the hard work by making a copy of an existing root filesystem and modifying some files for the DC. In the Etherboot distribution, there is a tutorial and links to a couple of shell scripts that will create such a DC root filesystem from an existing server root filesystem. There are also troubleshooting tips in the Etherboot documentation as this is often the trickiest part of the setup. The customised Linux kernel for the DC expects to see the root filesystem at /tftpboot/(IP address of the DC), for example: /tftpboot/192.168.1.100 in the case above. This can be changed when configuring the kernel, if desired. Now create or edit /etc/exports on the server and put in a line of the following form: /tftpboot/192.168.1.100 aldebaran.foo.com(rw,no_root_squash) The rw access is needed for various system services. The no_root_squash attribute prevents the NFS system from mapping root's ID to another one. If this is not specified, then various daemons and loggers will be unhappy. Start or restart the NFS services (rpc.portmap and rpc.mountd) and retry the diskless boot. If you are successful, the kernel should be able to mount a root filesystem and boot all the way to a login prompt. Most likely, you will find several things misconfigured. Most Linux distributions are oriented towards disked operation and require a little modification to suit diskless booting. The most common failing is reliance on files under /usr during the boot process, which is normally imported from a server late in the boot process. Two possible solutions are: 1. Provide the few required files under a small /usr directory on the root filesystem, which will then be overlaid when /usr is imported, and 2. Modify the paths to look for the files in the root filesystem. The files to edit are under /tftpboot/192.168.1.100 (remember, this is the root directory of the DC). You may wish to mount other directories from the server, such as /usr (which can be exported read-only). When you are satisfied that you can boot over the network without any problems, you may wish to put the code on an EPROM. An EPROM programmer starts at around $100 US, and is not a cost effective investment for a hobbyist who uses it sporadically. Occasionally one will appear on the used market at a bargain price, the main caveat being to ensure that the software to drive it is available. A proficient electronics hobbyist could build one using one of the several free designs published on the Internet, but for the majority of readers, the best solution is to make the acquaintance of someone who has access to one, perhaps someone in an electronics hobbyist group or working in the electronics industry. A short note on EPROM technology: The bits of an EPROM are programmed by injecting electrons with an elevated voltage into the floating gate of a field-effect transistor where a 0 bit is desired. The electrons trapped there cause that transistor to conduct, reading as 0. To erase the EPROM, the trapped electrons are given enough energy to escape the floating gate by bombarding the chip with ultraviolet radiation through the quartz window. To prevent slow erasure over a period of years from sunlight and fluorescent lights, this quartz window is covered with an opaque label in normal use. There is another technology, called EEPROM or Electrically Erasable PROM, sometimes called Flash PROM. Here the bits are cleared by an electrical signal. This obviates the need for an ultraviolet eraser if the EPROM is to be reused, but requires additional circuitry to support the erase phase. If one is handy with electronics, there is a contributed circuit design and driver software for an EEPROM board in the Etherboot distribution. The board is plugged into any spare ISA bus slot on a PC and boots a network card plugged into some other slot. 2.4. Uses of Network booting X-terminals are one natural use of network booting. The lack of a disk in the terminal makes it quieter and contributes to a pleasant working environment. The machine should ideally have 16MB of memory or more and the best video card you can find for it. This is an ideal use for a high-end 486 or low-end Pentium that has been obsoleted by hardware advances. Other people have used network booting for clusters of machines where the usage is light on the DC and does not warrant a disk, e.g. a cluster of classroom machines. 2.5. For more information Your first stop should be the Etherboot home page: There you will find links to other resources, including a mailing list you can subscribe to, where problems and solutions are discussed. 3. Begin setup 3.1. Document Changes Following are the history of changes to this document: · v0.0.3 12 Sep 1996: Some minor error fixes · v1.0.0 13 May 1999: Added some useful URLs. Changed this HOWTO to main HOWTO from mini-howto. Also rewrote this HOWTO using SGML tool. Added more chapters written by Ken Yap, Robert Nemkin. 3.2. How to set up a diskless Linux box This document is about setting up a diskless Linux box. Sometimes it might be necessary to run Linux on PC's which have neither hard disks nor floppy drives. If a network, another Unix system with bootp, tftp, an NFS server, and an eprom burner is available then it is possible to set up and operate Linux without hard/floppy disks. 3.3. Related documents · NFS-root Mini Howto · Linux NET-2/3-HOWTO by Terry Dawson, 94004531@postoffice.csu.edu.au · /usr/src/linux/README about configuring and compiling new kernels 3.4. How does it work? · 1.Diskless computer (DC) broadcasts MAC address with bootp: Who am I? · 2.Bootp or DHCP server on S looks up DB: Your IP address is X.X.X.X, your server is S, your boot file is vmlinuz.myname, etc. · 3.DC asks to load file from TFTP server on S: Please give me vmlinuz.myname · 4.S: Here you are (/tftpboot/vmlinuz.myname) DC thinks a while (booting Linux). · 5.DC: Please let me mount / with NFS · 6.S: Here is your root FS (/tftpboot/IPnumber). (In 2.2 kernels, /tftpboot/domainname.) · 7.DC: Please let me mount other NFSes (/usr, /home/, etc) · 8.S: Here you are · 9.DC: Runs intended application Network boot ROM contains code to do 1 and 3. 3.5. Hardware Whatever is described here was checked on the following configuration · Sun-OS 4.1.3 as boot server · Slackware 2.3 + Linux 1.2.8 + wd 8013 ethercard. · Working Ethernet lan 4. Fundamental ideas The fundamental idea is as follows: the PC will get its IP address from the boot server via the bootp protocol, using 0.0.0.0 as the initial IP address and its kernel via the tftp protocol. (-- Booting across segments (via router) not a simple question, so either put both the server and the diskless boxes on the same lan segment or configure an UDP helper address in your router to the address of the server. Refer to your router product manual for further info.--) For this follow the steps below. 4.1. Setting up the PC Get the nfsboot package (the package is available from your favourite linux mirror site in the /pub/Linux/system/Linux-boot directory). It contains a booteprom image for the wd8013 card which can be directly burned in. There are alternative ways to prepare the PC: · If your machine is not quite diskless, then you may use the little DOS program, or · The binary floppy image contained in the same package. If you choose the latter option you must write the image onto a floppy by the dd command. These images contain a bootp and tftp client. You need to prepare a linux kernel too, which contains the nfs-root option. · If you are using the latest stable kernel, linux-1.2.13, then you need to patch the kernel with the patchfile included in the nfsboot package (-- Refer to patch(1)--) · If you try to use the latest, but unstable kernel from the linux-1.3.x series, then you have to configure in the nfs-root option. You may or may not configure block device (floppy or hard disk) support, but you must configure tcp/ip support, wd ethernet card support, nfs filesystem support. Then recompile the kernel as usual. 4.2. Setting up a bootpd on the server It can be found in package bootpd-2.4.tar.gz (which can be found on your favourite linux mirror site in the /pub/Linux/system/Network/boot.net directory). Get the package, compile and install it. If your other Unix box happens to be a Slackware Linux then you may skip this step for the standard distributions contain a bootpd. The daemon can be run either directly by issuing command ______________________________________________________________________ bootpd -s ______________________________________________________________________ or by using inetd. In this case you need to edit: · /etc/inetd.conf to remove the hashmark from the start of these lines: ______________________________________________________________________ # tftp dgram udp wait root /usr/sbin/in.tftpd tftpd /export # bootps dgram udp wait root /usr/sbin/in.bootpd bootpd ______________________________________________________________________ · insert or uncomment the following two lines in /etc/services: ______________________________________________________________________ bootps 67/tcp # BOOTP server tftp 69/udp # TFTP server ______________________________________________________________________ · restart inetd by ______________________________________________________________________ kill -HUP . ______________________________________________________________________ 4.3. Configure the bootpd on the server First of all, bootpd have a config file called bootptab which usually resides in /etc. You must modify it by inserting the IP addresses of your gateway, dns server, and the ethernet address(es) of your diskless machine(s). An example /etc/bootptab: ______________________________________________________________________ global.prof:\ :sm=255.255.255.0:\ :ds=192.168.1.5:\ :gw=192.168.1.19:\ :ht=ethernet:\ :bf=linux: machine1:hd=/export/root/machine1:tc=global.prof:ha=0000c0863d7a:ip=192.168.1.140: machine2:hd=/export/root/machine2:tc=global.prof:ha=0800110244e1:ip=192.168.1.141: machine3:hd=/export/root/machine3:tc=global.prof:ha=0800110244de:ip=192.168.1.142: ______________________________________________________________________ global.prof is a general template for host entries, where · sm field contains the subnet mask · ds field contains the address of the Domain Name Server · gw field contains the default gateway address · ht field contains the lan media hardware type · bf field contains the name of the boot file After this, every machine must have a line: · the first field contains the host name, · hd field contains the directory of the bootfile, · the global template can be included with the tc field, · ha field contains the hardvare address of the ethernet card, · ip field contains the assigned ip address. 4.4. Understanding tftp TFTP (Trivial File Transfer Protocol) is a file transfer protocol, such as ftp, but it's much simpler to help coding it in EPROMs. TFTP can be used in two ways: · simple tftp: means that the client can acces to your whole file system. It's simpler but it's a big security hole (anyone can get your password file via tftp). · secure tftp: the tftp server uses a chroot.2 system call to change it's own root directory. Anything outside the new root directory will be completelly inaccessible. Because of the chroot dir becomes the new root dir, the hd filed in the bootptab must reflect the new situation. For example: when using insecure tftp, the hd field contains the full path to the boot directory: /export/root/machine1. When using secure tftp whith /export as root dir, then /export becomes / and the hd field must be /root/machine1. Almost every Unix implementation contains tfpt server, probably you don't need to install your own one. Install tftpd, make sure it's active in /etc/inetd.conf, typical line tftp dgram udp wait root /usr/sbin/tcpd in.tftpd /tftpboot 4.5. Kernel Image You must compile a kernel for the DC that includes NFS support and NIC driver compiled in (not modules). Answer yes to Root file system on NFS? and BOOTP support? After building the kernel, run mknbi-linux from the Etherboot distribution on it. Install this tagged image as /tftpboot/(bf attribute in bootptab). 4.6. Setting up a minimal Linux configuration on the remote server This may contain packages a, ap, n, and x of the Slackware distribution. To install more is OK; however the above packages suffice for the purposes of a diskless X terminal. For the installation you need a working Linux system. Find some disk space on the remote machine and export it read-write. Mount the exported directory onto somewhere (e.g. /mnt) on the file system of the Linux box. Start Linux setup and change the root option in the setup from / to /mnt. Then setup the above packages as usual. If you want to run no more than one diskless Linux then no changes are needed. On the other hand, if you plan to use more than one diskless machine then the above setup will not work because some files and directories must be private to the machines. The problem can be bypassed by moving the /usr (it contains no private data) and then create a separate subdir for each diskless machine. For example, if /export/linux/machine1 were mounted to /mnt then the directory structure after the initial setup will look like ______________________________________________________________________ /export/linux/machine1/bin /export/linux/machine1/sbin /export/linux/machine1/lib /export/linux/machine1/etc /export/linux/machine1/var /export/linux/machine1/usr ______________________________________________________________________ After the changes you will have ______________________________________________________________________ /export/linux/machine1/bin /export/linux/machine1/sbin /export/linux/machine1/lib /export/linux/machine1/etc /export/linux/machine1/var /export/linux/usr ______________________________________________________________________ Now create the subdirectories for the other machines. Assume for now that your diskless machines are called machine1, machine2, machine3, etc.; then you may use the following bash script to setup the other directories ______________________________________________________________________ cd /export/linux for x in machine2 machine3 ; do mkdir $x; cd $x (cd ../machine1; tar cf - *) | tar xvf - done ______________________________________________________________________ Then do the following export: · /export/linux/usr readonly for everyone. · /export/liunx/machine1 only to machine1 with rw,root rights. · /export/liunx/machine2 only to machine2 with rw,root rights. · /export/liunx/machine3 only to machine3 with rw,root rights. as follows (-- the format of this example follows the SunOs 4.1.3 exports file syntax--) : ______________________________________________________________________ # This file is /etc/export # for remote linux X terminals by Buci # this line is only once /export/root/usr -access=linuxnet # these lines once for every host /export/root/machine1 rw=machine1,root=machine1 /export/root/machine2 rw=machine2,root=machine2 /export/root/machine3 rw=machine3,root=machine3 ______________________________________________________________________ Don't forget to run exportfs -a. 4.7. Configuring the tftp server Now it is time to configure the tftp server. If you do not need secure tftp then everything is quite simple for your clients can be booted from the /export directory. If a secure tftp is used then you can either make a full /export/linux directory structure under /tftpboot (with a single real kernel and symbolic links for the other machines), or let the /export directory be the boot directory of the secure tftpd. Or, if you have a separate tftpboot directory then, similarly, you need only the original directory structure with a single kernel and symbolic links for the others. You can achieve this setup by typing the following: ______________________________________________________________________ mkdir -p /tftpboot/export/linux/machine1 cd /tftpboot/export/linux/machine1 cp /export/linux/machine1/ . ______________________________________________________________________ Then type the following: ______________________________________________________________________ mkdir -p /tftpboot/export/linux/machine2 cd ../machine2 ln -s ../machine2/ ______________________________________________________________________ 4.8. Final work Finally, you must insert ______________________________________________________________________ /sbin/mount nfs_server:/export/linux/usr /usr ______________________________________________________________________ as the first line of ______________________________________________________________________ /export/linux//etc/rc.d/rc.S ______________________________________________________________________ where stands for machine1, machine2, etc. 4.9. Net Loader A small program that runs as a BIOS extension, usually on an EPROM on the NIC. It handles the BOOTP query and TFTP loading and then transfers control to the loaded image. It uses TCP/IP protocols but the loaded image doesn't have to be Linux. The loaded image can be anything, even DOG. There are two free implementations of TCP/IP net loaders: Etherboot and Netboot : Etherboot uses built-in drivers while Netboot uses Packet drivers. They can also be loaded from a floppy for testing and for temporary setups. 4.10. RH5 configuration The DC requests to mount /tftpboot/(IP address of DC) (in 2.1 and above: /tftpboot/(name of DC in bootptab) ) as its / by NFS from server. You must export this from the server (rw, no_root_squash) because the DC wants to write on it (log files, etc). The / must contain /sbin, /bin, /lib, /etc, /var, /tmp, /root, /dev and /proc. /sbin, /bin, /lib/ can be a copy of an existing RH5 system. They can be shared between all DCs. But hard links only. BTW, don't link to server originals. /etc, /var and /dev should be non-sharable copies. Customise /etc/sysconfig/network, /etc/sysconfig/network-scripts/ifcfg-eth0, /etc/fstab, /etc/conf.modules, and others. Turn off all network services you don't need. Remove all stuff you don't need from /var, e.g. RPM db, lpd files. /root and /proc should just exist. /tmp should exist and be mode 1777. You probably want to create /usr and /home mount points. /usr can be mounted ro. About 10 MB per DC plus about 15 MB of shared files should be sufficient. BTW: if your DCs are quite similar, the kernel image can also be shared. Here is an illustrative script to create the first root filesystem. #!/bin/sh if [ $# != 1 ] then echo Usage: $0 client-IP-addr exit 1 fi cd / umask 022 mkdir -p /tftpboot/$1 # just make these ones for d in home mnt proc tmp usr do mkdir /tftpboot/$1/$d done chmod 1777 /tftpboot/$1/tmp touch /tftpboot/$1/fastboot chattr +i /tftpboot/$1/fastboot # copy these ones cp -a bin lib sbin dev etc root var /tftpboot/$1 cat <company->Hardware->Peripherals->Device programmers. Click on this site · Yahoo URL for EPROMs at · Advanced Research Technology B.V - development, production and sales of electronic programmer equipment; development of hard- and software. · Advin Systems Inc. - PC-based device programmers that support the latest in package types and device technologies. · Andromeda Research Labs - manufactures a portable eprom and device programming system. · B and C Microsystems, Inc - offers test and duplication/programming equipment for PCMCIA (PC) Cards, ISA/PCI Cards, SIMMs, Memory Devices (including FLASH), PLDs. · BP Microsystems - Device Programmers. · Bytek - designs, develops, manufactures and markets micro-processor-based, modular electronic systems used to program and test semiconductor devices. Product line includes the ChipBurner. · Concentrated Programming Ltd - offers a full range of device programming solutions. · Dataman Programmmers Ltd. - manufacture of hand-help EPROM programmer/emulator. Also sell PC-based programmers, and Gang-Pro programmers. · General Device Instruments - IC Device programmers. Universal and Gang programmers for Pld, Flash, microcontrollers, Proms, EEproms, Memory, Epld, Mach and many other ic devices. · HI-LO System Research Co., Ltd. - manufacturer of universal and gang device programmers. · ICE Technology - EPROM and universal device programmers which support memories, microcontrollers, and programmable logic devices. · Iceprom - in-circuit erasable programmable read-only memory. · Incept Ltd. · International Microsystems Inc - High speed reliable gang programmer. (PROM, FLASH, Microcontroller, PCMCIA memory card). · JED Microprocessors Pty. Ltd. - plugs into a PC printer port D25 connector, and programs any 28-pin or 32-pin EPROM and FLASH device. · Logical Devices, Inc - device programming for PLDs, FPGAs, PROMs, microcontrollers. Producers of CUPL compiler for programmable logic and the ALLPRO and Chipmaster device programmer. · MCL Systems - new method not only for programming but also for developing your new hardware with Integrated Controller Unit. And you don't need to be an expert. · MQP Electronics - manufacturer of universal device programmers, gang programmers, production software, and package converters. High thoughput and reliability. · Needham's Electronics - manufacturer of device programmers. · NP Programming Services - provides programming for memory and logic parts. · Program Automation, Inc. - independent service company specializing in high volume PROM programming, including flash I/Cs. · Stag Programmers Inc - manufacturer of prom and logic programmers, production handling equipment and UV erasers. · Sunrise Electronics - universal device programmers, gang and in-circuit programmers with life time support. · System General Co. - Device Programmer, EPROM Writer and IC Tester · Tribal Microsystems - universal and gang device programmers, 8051 and EPROM emulators, test and burn-in sockets and production sockets. · Universal Device Programmers 6.2. Non-Volatile Memory chips This chapter gives brief descriptions of memory chips. · PROM: Pronounced prom, an acronym for programmable read-only memory. A PROM is a memory chip on which data can be written only once. Once a program has been written onto a PROM, it remains there forever. Unlike RAM, PROMs retain their contents when the computer is turned off. The difference between a PROM and a ROM (read-only memory) is that a PROM is manufactured as blank memory, whereas a ROM is programmed during the manufacturing process. To write data onto a PROM chip, you need a special device called a PROM programmer or PROM burner. The process of programming a PROM is sometimes called burning the PROM. An EPROM (erasable programmable read-only memory) is a special type of PROM that can be erased by exposing it to ultraviolet light. Once it is erased, it can be reprogrammed. An EEPROM is similar to a PROM, but requires only electricity to be erased. · EPROM: Acronym for erasable programmable read-only memory, and pronounced ee-prom, EPROM is a special type of memory that retains its contents until it is exposed to ultraviolet light. The ultraviolet light clears its contents, making it possible to reprogram the memory. To write to and erase an EPROM, you need a special device called a PROM programmer or PROM burner. An EPROM differs from a PROM in that a PROM can be written to only once and cannot be erased. EPROMs are used widely in personal computers because they enable the manufacturer to change the contents of the PROM before the computer is actually shipped. This means that bugs can be removed and new versions installed shortly before delivery. · EEPROM: Acronym for electrically erasable programmable read-only memory. Pronounced double-e-prom or e-e-prom, an EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge. Like other types of PROM, EEPROM retains its contents even when the power is turned off. Also like other types of ROM, EEPROM is not as fast as RAM. EEPROM is similar to flash memory (sometimes called flash EEPROM). The principal difference is that EEPROM requires data to be written or erased one byte at a time whereas flash memory allows data to be written or erased in blocks. This makes flash memory faster. · FRAM: Short for Ferroelectric Random Access Memory, a type of non- volatile memory developed by Ramtron International Corporation. FRAM combines the access speed of DRAM and SRAM with the non- volatility of ROM. Because of its high speed, it is replacing EEPROM in many devices. The term FRAM itself is a trademark of Ramtron. · NVRAM: Abbreviation of Non-Volatile Random Access Memory, a type of memory that retains its contents when power is turned off. One type of NVRAM is SRAM that is made non-volatile by connecting it to a constant power source such as a battery. Another type of NVRAM uses EEPROM chips to save its contents when power is turned off. In this case, NVRAM is composed of a combination of SRAM and EEPROM chips. · Bubble Memory: A type of non-volatile memory composed of a thin layer of material that can be easily magnetized in only one direction. When a magnetic field is applied to circular area of this substance that is not magnetized in the same direction, the area is reduced to a smaller circle, or bubble. It was once widely believed that bubble memory would become one of the leading memory technologies, but these promises have not been fulfilled. Other non-volatile memory types, such as EEPROM, are both faster and less expensive than bubble memory. · Flash Memory: A special type of EEPROM that can be erased and reprogrammed in blocks instead of one byte at a time. Many modern PCs have their BIOS stored on a flash memory chip so that it can easily be updated if necessary. Such a BIOS is sometimes called a flash BIOS. Flash memory is also popular in modems because it enables the modem manufacturer to support new protocols as they become standardized. 7. Etherboot 7.1. Introduction This is the README file for the Etherboot package. This document explains how to install, configure and use the Etherboot package. The instructions here apply to version 4.0 of Etherboot. Etherboot is a package for creating ROM images that can download code over the network to be executed on an x86 computer. Typically the computer is diskless and the code is Linux, but these are not the only possibilities. The code uses the bootp, tftp and NFS Internet Protocols. 7.1.1. What hardware is supported? Etherboot supports the following network hardware (in no particular order): 3c503, 3c507, 3c509, 3c905b, NE1000, NE2000 (also the PCI cards, with the nepci driver), WD8003, WD8013, SMC8216/8416, Lance based cards such as the NE2100 and NI6510 (also the PCI Lance cards), Crystal CS89x0, Intel EtherExpress Pro, SMC 83c170 EPIC/100, SMC9000, Realtek 8139, NI5210, Schneider and Koch G16, and Tiara (Fujitsu Lancard). All Etherboot drivers are autoprobing, which means they attempt to detect the hardware addresses at which the card is installed. It's fairly easy to write a driver if you are familiar with Ethernet hardware interfacing. Please contact me for more information if you are interested in doing so or are interested in having a driver written. 7.1.2. Availability of this document This document and related documents are also kept online at the Etherboot Home Page . This will in general have the latest distributions and documentation. For a talk/tutorial type introduction to what Etherboot does and how to set it up, see my SLUG talk . You may wish to review this before reading further. An older version of this README, which is now out of date, can be accessed via this link . 7.1.3. Getting help There is a mailing list for all netbooting related issues. To subscribe follow the instructions on the Etherboot home page . With the exception of the following section, the information on diskless booting is not specific to Etherboot but can be used for the Netboot package also. 7.2. Unpacking, compiling and testing the package This section is Etherboot specific. 7.2.1. Unpacking the distribution Unpack the distribution using gunzip and tar, using either of the following commands: ______________________________________________________________________ tar zxvf etherboot-4.0.tar.gz gunzip < etherboot-4.0.tar.gz | tar xvf - ______________________________________________________________________ 7.2.2. Compiling the ROM images Precompiled ROM images are provided in the bin/ directory but you may wish to review the options compiled in and make your own versions. For the 32 bit version you need a recent release of gcc and the binutils tools. This package was compiled with the tools from a RedHat 5.2 distribution but it should work with any recent Linux distribution. For the 16 bit version you need the bcc tools from the Embedded Linux Kernel Subset (ELKS) project, for more details see the notes on 16 bit Etherboot <16.html>. You need the 16 bit version only if you intend to run Etherboot on a 286 or 086/088 PC. Assuming you have decided to make the 32 bit version, you only have to go to src-32/, edit the options in Config and say make. This will create all the ROM images available. The .lzrom images are the same as the .rom images. Since the .lzrom images are smaller and work exactly the same, there is no real reason to use .rom images any more, unless you are nervous about compression algorithm patents. We believe the algorithm used does not infringe patents, having been in public use for some time, but we do not know all the legal ramifications. See here for more details. Here is a brief description of the options available: ______________________________________________________________________ Basic options: -DDHCP_SUPPORT - Use DHCP instead of BOOTP (default on) -DIMAGE_MENU - Allow to interactively chose between different bootimages; read vendortags.html for further information. -DMOTD - Display message of the day; read vendortags.html for further information. -DANSIESC - evaluate a subset of common ANSI escape sequences when displaying the message of the day; this probably does not make sense unless you also define -DMOTD or at least -DIMAGE_MENU. Combining this option with -DSERIAL_CONSOLE is a waste of EPROM space. -DGFX - support extensions to the ANSI escape sequences for displaying graphics (icons or logos); this requires -DANSIESC -DASK_BOOT=n - Ask "Boot from Network or from Local? " at startup, timeout after n seconds (0 = no timeout); this can be done in a more generic way by using the IMAGE_MENU, but it requires that the "bootp" server is accessible, even when booting locally. -DANS_DEFAULT=ANS_NETWORK - Assume Network to previous question (alternative: ANS_LOCAL) on timeout or Return key See etherboot.h for prompt and answer strings. -DEMERGENCYDISKBOOT - if no BOOTP server can be found, then boot from local disk. The accessibility of the TFTP server has no effect, though! So configure your BOOTP server properly. Basic options only on Etherboot/32: -DPASSWD - enable password protection for boot images; this requires -DIMAGE_MENU -DUSRPARMS - allow the user to interactively edit parameters that are passed to the booted kernel; you should probably enable -DPASSWD as well; this feature requires -DIMAGE_MENU -DFLOPPY - boot from floppy/hd if bootimage matches the pattern "/dev/[fh]d*"; if you do not have enough space in the EPROM, then disable this feature and use "mknbi-blkdev" for booting from a local blockdevice. -DCONFIG_PCI_DIRECT - define this for PCI BIOSes that do not implement BIOS32 or not correctly These options should normally not need to be touched: -DNOINT19H - Take control as soon as BIOS detects the ROM Normally hooks onto INT19H -DMOVEROM - if your motherboard does not cache adapter memory space, then this option can speed up loading of compressed BOOT-Prom images. It has no effect on uncompressed images. Unless you are very tight on free space, you will usually want to define this option. -DDELIMITERLINES - print a line of = characters at the start and also just before starting an image. -DSIZEINDICATOR - update a running total of the amount of code loaded so far, in kilobytes -DT509HACK - send two bootp packets before waiting for a reply to the first. Makes a 3c509 do bootp quicker -DT503_AUI - Use AUI by default on 3c503 cards. These options are only for a serial console for Etherboot/32: -DSERIAL_CONSOLE- use a serial line for input and output -DCOMPORT - 0x0 for COM1, 0x1 for COM2 etc -DCOMPARM - configuration for COMPORT, save values: 0xe3 == 9600/8n1, 0xa3 == 2400/8n1 ______________________________________________________________________ 7.2.3. Testing the ROM images You can test the image with a floppy before burning an EPROM. On Linux just put a blank floppy in fd0 and say make card.fd0 where card is the name of your network card and it will copy a bootable image onto the floppy. If you wish to do this by hand, it's easy, just prepend floppyload.bin to card.rom (or card.lzrom) and write this combined binary to the floppy raw, i.e. starting at the boot block. Like this: ______________________________________________________________________ cat floppyload.bin 3c509.lzrom > /dev/fd0 ______________________________________________________________________ When you boot with this floppy it will load the Etherboot ROM image from floppy and execute it. It should be able to detect your card. To get the bootrom to acquire an IP address and load the intended code, you need to set up bootp, tftp and NFS services, which we will discuss next. We suggest you continue to use floppy booting until you have completed the setup of the server and are satisfied that diskless booting works. 7.3. Setting up a diskless boot In this section I assume you want to boot a Linux kernel. Booting a DOS kernel is similar, the main differences being in the way you set up the tagged image. 7.3.1. Making a tagged image Etherboot expects to download a tagged image containing the code to be executed. Briefly explained, a tagged image is a wrapper around the pieces of code or data that need to be put in various places in the computer's memory. It contains a directory telling how large the pieces are and where they go in memory. It also says where to start execution. A tagged image is created using a utility program. The utility program is specific to the kernel you want to load. The version for Linux is called mknbi-linux and that for DOS is mknbi-dos. These utilities are found in the netboot- directory of the distribution. 7.3.2. Compiling a custom kernel You will probably have to compile a custom kernel because the kernel needs to have the "Root file system on NFS" option compiled in. You should also select "BOOTP support". "RARP support" is not needed. In 2.2 kernels you have to enable the "Kernel Autoconfig" option to access the BOOTP support question. And unless you are using an initrd (initial ramdisk) you will probably have to compile in the driver for your network card too. For details, see the file /usr/src/linux/Documentation/nfsroot.txt in a Linux kernel source distribution. After you have compiled the custom kernel, make the tagged image, typically like this: ______________________________________________________________________ mknbi -x -k zImage -o /tftpboot/vmlinuz.xterm ______________________________________________________________________ Then put the tagged image in where the tftp daemon expects to find it, typically /tftpboot. Make sure it is world-readable because typically the tftp daemon runs as an unprivileged user. 7.3.3. Setting up a bootp daemon Now set up a bootp daemon. In RedHat 5.2 this means installing the bootp RPM package, making sure that the bootps service is active in /etc/inetd.conf, and editing /etc/bootptab. The essential pieces of information you need to put in bootptab are: 1. The domain name of the machine. 2. The Ethernet (MAC) address of the network card, which you generally obtain from a sticker on the card, a configuration program for the card, or in the last resort, from watching the output of Etherboot or from the packets sent from the card when trying to boot, using the debug option of bootpd. 3. The name of the tagged image file, relative to the tftpboot directory. 4. The IP address you intend to give it. 5. The IP addresses of various servers. You will need at least the tftp server's address. Here is an example of a /etc/bootptab for the bootpd supplied with RedHat Linux 5.2 and probably many versions of Unix: ______________________________________________________________________ .default:\ :ht=ethernet:\ :hd=/tftpboot:bf=null:\ :ds=nameserver:\ :hn:to=36000: xterm.ken.net.au:tc=.default:ha=08002BB7F380:ip=192.168.26.100:bf=vmlinuz.xterm ______________________________________________________________________ The first entry sets up some common defaults which applies to all succeeding entries which can be "included" using the tc=.default attribute. The first field is the domain name of the machine. The ha attribute is the Ethernet address. The ip attribute is self- explanatory. The bf field specifies the tagged image filename. For more details, consult the bootptab man page. Please note that if you use the ef (extension file) attribute to be able to send more configuration data to the diskless machine, you must run bootpef everytime bootptab is modified. If you are on a local network that is not directly connected to the Internet, you can use the "private" IP addresses 192.168.x.y (or in the other ranges mentioned in RFC1918 ). Otherwise please ask either your network administrator or your Internet service provider for your own IP address(es). 7.3.4. Setting up a DHCP daemon As an alternative to bootp, you could set up a DHCP server which has the advantage of automating the handing out of IP addresses. However the kernel may still do a bootp request to find the IP address for mounting the NFS filesystem. You may then wish to investigate the option in mknbi-linux which tells the kernel to take the address from the initial DHCP reply. More information about DHCP can be found at the DHCP FAQ Web Page . 7.3.5. Setting up a tftp daemon Now set up a tftp daemon. In RedHat 5.2 this means installing the tftp RPM package and making sure that the tftp service is active in /etc/inetd.conf. You probably want to use the secure (-s) option so that files can only be fetched from /tftpboot or people may be able to fetch arbitrary files from your server. 7.4. Testing the network booting Now when you start up Etherboot, it should obtain an IP address and print out what it received. If you do not get this to work, turn on debugging in bootpd and see if any query was received. If not, check your network hardware (cables, etc). If a query was received, check if bootpd was able to give an answer. If not, then the Ethernet address was not found in /etc/bootptab. If a reply was sent, then only faulty hardware or a bug in Etherboot would prevent it being received by Etherboot. Assuming an IP address was received, the next thing Etherboot tries to do is load a file using tftp. Check your system logs to see if a tftp daemon was started up and a file requested. Generally if you run tftpd under tcpwrapper security, a log entry will be generated. If not, it could be a path problem or file permission problem (the file needs to be readable by tftpd). Fix the problem. After the tagged image is loaded, Etherboot will jump to it. If it crashes here, check that the image is a tagged image. If it executes and stops at the point where it's trying to mount the NFS root, then you need to check that you have the "root on NFS" option compiled in and that you have compiled in the network card driver. 7.4.1. Setting up a NFS root filesystem Now you need to set up a NFS root filesystem for the diskless computer. Typically this is under /tftpboot/. (In 2.1 and presumably future kernels, this should be /tftpboot/). This needs to contain a complete root filesystem that will make the kernel boot happily. This means, for most kernels, it should contain /dev, /proc, /etc, /sbin, /bin, /tmp and /var. The details vary from distribution to distribution. Being lazy I just make a copy of the necessary files from an existing RedHat 5.2 filesystem and modify some key files appropriately. You can find a description in my tutorial and some shell scripts to copy the files. Since the amount of disk space needed is relatively small in these days of large disks, I don't bother to throw out things that may not be needed. Warning: Do not attempt to reuse the root filesystem of your server, whether by exporting it directly or by making hard links (symbolic links will not work). First of all, the configuration files will contain information pertaining to the server, not the client, so your client will get the wrong information. Secondly, this is a security risk. NFS is already not totally safe, but this way you are directly exposing your server root to clients. Even if you make hard links, the clients could (maliciously or accidentally) overwrite key binaries, making the server unusable. Don't try to save a few megabytes of disk space this way. You can however share some directories between clients, typically /sbin, /bin and /lib. The sample scripts in the tutorial show you how. The root filesystem should be exported rw and no_root_squash because the various processes need to be root and need to write to log files in the root partition. You may wish to export /usr and /home filesystems to the diskless computer also. These do not need no_root_squash permission. Be aware that the RedHat 5.2 distribution has a few "bugs" relating to symlinks and so forth for diskless booting. These are mentioned in the tutorial. Other distributions may have similar problems. 7.4.2. Swap over NFS Swap over NFS can be arranged but you have to patch the kernel source. There is a patch for kernels in the contrib/ directory for 2.0.x kernels. Hopefully this will make it into future kernels. Be aware that opinions are divided on NFS swap. Some people think it's a bad thing because it just kills the network if you have lots of diskless computers and that you shouldn't be running into a swap regime on a diskless computer anyway. Some other people like having a bit of insurance. There are patches in the contrib directory for NFS swap but for up to date patches, try here < http://www.math1.rwth-aachen.de/~heine/nfs- swap/>. Also have a look at the NBD Network Block Device web page for swapping over that. This requires a 2.1 or 2.2 kernel. 7.5. Booting DOS What about DOS? The deal with DOS is that one is loading a virtual floppy called A: into extended memory and then booting from this floppy. So you have to capture an image of a bootable DOS floppy first. Some more details can be found in the mknbi-dos directory. I have booted DOS (both M$ and DR versions) diskless this way. Note that extended memory is used so that rules out 086/088 computers but 286s are ok. See this document for more details. If you were thinking of booting a Windows machine via the network, it seems (I'm not masochistic enough to do this) the problem is not the network booting but the mounting of a file system over NetBIOS (Windows does not do remote mounts of root filesystems over NetBIOS on TCP). So that rules out a Samba server. It appears to be possible over a Netware server, for which Linux has workalikes. But then what do you do about the networking stack? This situation may change with with future Samba developments. But you will still have problems with pathnames and the usual Windows hassles. Do you really want to do this? In the Web page for Etherboot , there is a link to someone's Web page explaining how this was done with a commercial TCP/IP boot ROM. 7.6. Making an Etherboot EPROM or EEPROM Assuming you have satisfactorily set up your server environment, you may now wish to put the Etherboot onto an EPROM or EEPROM. Naturally this assumes access to hardware to burn (and possibly erase) EPROMs. An alternative is to use an EEPROM card. There is a schematic and PCB artwork for such a card in the distribution. This EEPROM card plugs onto the ISA bus and can be reprogrammed with software. 7.6.1. Choosing the EPROM Most network cards come with a blank (E)EPROM socket even though it is seldom used. When it is used, it is typically filled with a proprietary EPROM from the network card manufacturer. You can put an Etherboot EPROM there instead. 7.6.2. Enabling the EPROM First you must discover how to enable the EPROM socket on your card. Typically the EPROM is not enabled at the factory and a jumper or a soft configuration is used to turn it on. 7.6.3. Size and speed of the EPROM Secondly, you must discover what size and speed of EPROM is needed. This can be difficult as network card manufacturers often neglect to provide this information. The smallest EPROM that is accepted by network cards is an 8K EPROM (2764). Some cards will even go up to 64KB EPROMs (27512). You want to use the smallest EPROM you can so that you don't take up more of the upper memory area than needed as other extensions BIOSes may need the space. However you also want to get a good price for the EPROM. Currently the 32KB and 64KB EPROMs (27256 and 27512) seem to be the cheapest per unit. Smaller EPROMs appear to be more expensive because they are out of mainstream production. If you cannot find out from the documentation what capacity of EPROM your card takes, you could do it by trial and error. Take an ROM with some data on it (say a character generator ROM) and plug it into the socket. Be careful not to use an extension BIOS for this test because it may be detected and activated and prevent you from booting your computer. Using the debug program under DOS, dump various regions of the memory space. Say you discover that you can see the data in a memory window from CC00:0 to CC00:3FFF (= 4000 hex = 16384 decimal locations). This indicates that a 16 KB EPROM is needed. However if you see an alias in parts of the memory space, say the region from CC00:0 to CC00:1FFF is duplicated in CC00:2000 to CC00:3FFF, then you have put an 8 KB EPROM into a 16 KB slot and you need to try a larger EPROM. Note that because pinouts for 28 pin EPROMs are upward compatible after a fashion, you can probably use a larger capacity EPROM in a slot intended for a smaller one. The higher address lines will probably be held high so you will need to burn the image in the upper half or upper quarter of the larger EPROM, as the case may be. However you should double check the voltages on the pins armed with data sheet and a meter because CMOS EPROMs don't like floating pins. The speed of the EPROM needed depends on how it is connected to the computer bus. If the EPROM is directly connected to the computer bus, as in the case of many cheap NE2000 clones, then you will probably have to get an EPROM that is at least as fast as the ROMs used for the main BIOS. This is typically 150 ns. Some network cards mediate access to the EPROM via an ASIC and this ASIC may insert wait states so that slower EPROMs can be used. Incidentally the slowness of the EPROM doesn't affect Etherboot execution speed much because Etherboot copies itself to RAM before executing. I'm told Netboot does the same thing. 7.7. Troubleshooting tips · Floppy boot doesn't work. Have you copied the ROM image (with the floppyloader prepended) to the floppy raw? Is that size of floppy bootable by your computer? Are you trying to run a 32 bit Etherboot on a 16 bit machine (286, 086/088)? Have you selected too many compile time options? The real limit on Etherboot is not the size of the EPROM but the fact that it executes in the 32 KB region between 0x98000 and 0xA0000. If the sum of code, stack and bss is greater than 32 KB, then Etherboot might crash at unexpected places. You could increase the memory to 48 KB by lowering the RELOCADDR in the Makefile but this is outside the specifications. Definitely do not lower RELOCADDR below 0x94000 because various pieces of booting information are stored from 0x90000 upwards. · Floppy version works but EPROM version doesn't work. There is a program called rom-scan (Linux and DOS versions) in the directory contrib/rom-scan which will help detect problems. · If the EPROM is not detected at all then the contents of the EPROM are not visible to the BIOS. Check that you have enabled the EPROM with any jumpers or soft configuration settings. Check that you do not have any conflicts in the memory address of the EPROM and any other hardware. Perhaps you have to prevent it from being mapped out by your BIOS settings. Or perhaps you have to shadow it with RAM. Maybe you put the code in the wrong half or wrong quarter of the EPROM. Maybe the access time of the EPROM is not low enough. You can also use the debug program under BIOS to examine the memory area in question. · If rom-scan says the EPROM is present but not active, then something prevented the BIOS from seeing it as a valid extension BIOS. This could be truncation of the EPROM window, maybe you have a larger EPROM in a slot meant for a smaller one. Maybe there is a checksum error in the EPROM due to some bits not properly programmed or the EPROM not being fast enough. In one case that we know of, the 3c503 network card, the ASIC actually returns 2 bytes of 80 80 in the end locations of the EPROM space. This apparently is a kind of signature. The makerom program in Etherboot compensates for this, but if the pattern is not 80 80, then the code needs to be modified. · If rom-scan says the EPROM is present and active, but BIOS does not see it, then perhaps the EPROM is located in an area that the BIOS does not scan. The range scanned is supposed to be 0xC0000 to 0xEF800 in increments of 2 KB but I have seen some BIOSes that continue the scan into the 0xF0000 page. Note that rom-scan will also detect other extension BIOSes mounted on your computer, for example VGA BIOSes and SCSI adapter BIOSes. This is normal. · Etherboot does not detect card. Are you using the right ROM image? Is the card properly seated in the computer? Can you see the card with other software? Are there any address conflicts with other hardware? Is the PCI id of the card one that is not known to Etherboot yet? In this case and where you think there is a bug in Etherboot, please contact the author with all details. · Etherboot detects card but hangs computer after detection. Some cards are booby traps while they are enabled. The typical offenders are NE2000s which will hang the bus if any access is made to the reset addresses while interrupts are active. You may need to do a hard reset of the computer, i.e. power down and up again before running Etherboot. · Etherboot detects card but does nothing after saying Searching for server. Check your network hardware. Did you select the right hardware interface (AUI, BNC, RJ45)? Is the cabling ok? If you have a Unix computer on the network and have root privileges, you could run tcpdump looking for broadcast packets on the bootps port. If the requests are getting sent out but no replies are getting back, check your bootpd setup. Also check if the server has a route to the client. · Etherboot obtains IP address but fails to load file. Check the tftp server. Is the tagged image file installed? Is the file world readable? Did you put the right home directory and boot filename in bootptab? · Etherboot loads file via tftp but Linux fails to boot. This is a large category. Here are some suggestions: · You do not have a private copy of the /, /etc, /var, ... directories · Your /dev directory is missing entries for /dev/zero and/or /dev/null or is sharing device entries from a server that uses different major and minor numbers (i.e. a server that is not running Linux). · Your /lib directory is missing libraries (most notably libc* and/or libm*) or does not have the loader files ld*.so* · You neglected to run ldconfig to update /etc/ldconfig.cache or you do not have a configuration file for ldconfig. · Your /etc/inittab and/or /etc/rc.d/* files have not been customized for the clients. · Your kernel is missing some crucial compile-time feature (such as NFS filesystem support, booting from the net, transname (optional), ELF file support, networking support, driver for your ethernet card). · Missing init executable (in one of the directories known by the kernel: /etc, /sbin, ?). Remember /sbin/init must be a real file, not a symlink. · Missing /etc/inittab · Missing /dev/tty? · Missing /bin/sh · System programs that insist on creating/writing to files outside of /var (mount and /etc/mtab* is the canonical example) The essence is that you must provide whatever is needed in the NFS root filesystem that your kernel needs to boot. This is somewhat distribution dependent. In the discussion above I solved the problem by making a copy of an existing root filesystem and modifying a few bits. Be aware that some, if not all, distributions contain bugs in their layout that hinder diskless mounting so you will have to fix any problems that arise. An example was a directory in /usr/X11R6/lib that needed to be writable, preventing /usr from being mounted ro. · Etherboot works fine and kernel starts but network interface doesn't work. Check your network configuration in the OS. Etherboot uses polled I/O and not interrupt I/O to fetch the images. So the IRQ line doesn't get exercised. This manifested itself in one case with a NIC that could netboot but network programs run afterwards couldn't receive any packets. It seemed to be a combination of a weak NIC IRQ line and a fussy motherboard. But the same thing could happen if say the IRQ is not set to where the software is expecting it. The image will load fine with the wrong IRQ but the software will not run properly. This is more of an issue with say DOS packet drivers, where the user has to specify the IRQ line than with Linux, which autoprobes. 7.8. Acknowledgements The following people have contributed substantially to Etherboot. If you feel your name has been left out, just let me know and I will fix it up. Markus Gutschke Co-author of Etherboot. He was the person who ported the Netboot suite from FreeBSD. He has enhanced Etherboot with many features, one new driver and has contributed various utilities and addons. Gero Kuhlmann The mknbi utilities used by Etherboot are from Netboot. He has also clarified the original specification by Jamie Honan. Jamie Honan Jamie started Netboot off by writing the first version that used code from a packet driver. Martin Renters et. al The original authors of Netboot on FreeBSD. Bruce Evans Created bcc compiler used by Etherboot/16. Rob de Bath Current maintainer of bcc and associated tools like as86. Gerd Knorr Contributed MASQ for making a boot floppy without DOS. Adam Richter Contributed comboot for making a boot floppy without DOS. Claus-Justus Heine Contributed patch for serial console and NFS swapping. See the contrib/nfs-swap directory for his Web page. Dickon Reed Contributed display of loading status and a hack for the 3c509 card. David Munro Contributed PCI detection code originally from Linux sources. Charlie Brady Donated NE2100 card so that a driver could be written, and helped test the LancePCI driver. Spotted bug with 4.1 header code. Rogier Wolff Created Intel EtherExpressPro 100 driver and binary to hex converter. Vlag Lungu Contributed patches to work with DHCP. Also contributed a fix to match the received XID against the transmitted one, important in a network with many requesters. William Arbaugh Patches for eepro to work with 3.2. Jean Marc Lacroix Contributed an improved bin2intelhex. Jim Hague Contributed fixes to 3c503 driver for PIO mode, fix to makerom for presetting EPROM bytes, and various endian fixes. Andrew Coulthurst Contributed patch for making Intel eepro work in 4.0. Doug Ambrisko Contributed patches to start32.S from FreeBSD version to make it boot Windoze after answering N to Boot from Network question. Alex Harin Contributed patches for prepended loaders and makerom to make bootrom PnP and PCI compatible. Peter Dobcsanyi Contributed vendor and device IDs for the Netvin NE2000/PCI clone. adam@mudlist.eorbit.net Contributed RARP code as alternative to BOOTP/DHCP. Activated by RARP_NOT_BOOTP define. Daniel Engstrom Contributed a SMC9000 driver. Didier Poirot Contributed an Etherpower II (EPIC 100) driver. Martin Atkins Contributed mntnbi for mounting DOS NBIs. Atilla Bogar Contributed a bug fix to the bootmenu code and a patch to main.c to remove looping menus on failure. Also code for ARP replies and TFTP retransmit (#ifdefed). Cleanup of tftp and tftpd. Nathan R. Neulinger Found bug due to tu_block being declared signed short in arpa/tftp.h on many platforms when it should be unsigned short. David Sharp Contributed a FreeBSD driver for Tulip based cards. Ken Yap ported it to Etherboot. Not tested because code needs to be written for all the variants of the Tulip and also because no hardware available to me. Greg Beeley Contributed a 3c905b driver. Be sure to read the release notes in 3c905b.txt before using. Alex Nemirovsky Contributed patches to use BIOS call to size memory otherwise Etherboot was trampling on top of 640kB area, which is used by some extended BIOSes. Also contributed patches to pci.c to implement PCI bus support on BIOSes that do not implement BIOS32, or incorrectly. Guenter Knauf Suggested making the ASK_BOOT prompts more generic and clearer. (Why doesn't SGML-Tools accept üaut;?) Also contributed a DOS utility for extracting the identifier string and PCI IDs, if any, out of the boot ROM. Klaus Espenlaub Contributed various cleanup patches to the code especially in the bootmenu area, as well as a completely revamped start32.S. Also introduced Rainer Bawidamann's code, see next paragraph. Rainer Bawidamann Contributed a Realtek 8139 driver. Georg Baum contributed a Schneider & Koch G16 driver. jluke@deakin.edu.au sent in a fix for the WD/SMC8013 which I finally verified. 7.9. Copyright The boot code from FreeBSD is under the BSD license. The netboot code is under the GPL. This is not a problem really: the GPL states that mere aggregation of another work with a GPL'ed work on a storage medium, e.g. an archive file, does not put the other work under the GPL. Send changes to this document to Ken Yap (ken.yap@acm.org). 8. Netboot This chapter was written by Zurück zu Gero. The main site is at . 8.1. Introduction What do I need it for? The following list shows just a few examples of what Netboot can be used for: · Printer spooler · Terminal server · X11 terminal · Data logging system · Network-Computer (NC) · Some more .... Basically Netboot can be used for any cases in which a computer should be utilized without having a hard disk. But also for computers with a hard disk Netboot can be used if you want to hold just one operating system on your disk and additionally want to be able to boot a different system over the network. What operating systems are supported? Presently Netboot can boot Linux and MS-DOS. Since Windows-95 is also based on MS-DOS that can be used as well. In the future support is also planned for OS/2 and Free-BSD. However, Windows-NT will never be supported. The utility programs, which come with Netboot should run on an UNIX like system. What do I need in order to work with netboot? Obviously first of all you need one (or more) computers which should get bootet. Those are called clients. Netboot itself should be able to run on almost any PC compatible system, even with the oldest 8088 and 80286 processors. However, it has been optimized to run on 386 and up. Of course this system also needs a network card. Since Netboot uses standard DOS packet drivers, all network cards can be used for which packet drivers exist, even PCI and 100MBps cards. In case no such driver has been delivered with a network card it can usually be downloaded from an FTP server of the manufacturer, such as 3Com , SMC or Intel . In addition there are packet drivers for many popular network cards available for free from the Crynwr packet driver collection . Next you need a system which acts as the server. Because Netboot uses the BOOTP and TFTP standard protocols this server has to be able to understand those. It doesn´t matter if the server runs a UNIX like operating system or Windows-NT. What does it cost? Nothing! Netboot is given away for free and covered by the GNU General Public Licence . How does it work? In order to boot a computer without a hard disk a bootrom is necessary, which gets plugged into a socket on the network card. Netboot contains the full source code and executable binaries for such a bootrom. After poweron this bootrom queries a BOOTP server for the system´s network name and boot image file name, which then gets loaded using the TFTP protocol. This boot image file contains the operating system which get executed by the bootrom after loading. Netboot contains all necessary utilities to build such a boot image file for Linux and MS-DOS. 8.2. README 8.2.1. Copyright Notice, Acknowledgements You are allowed to modify and redistribute this code under the terms of the GNU General License. By making use of this software in any way you are automatically agreeing to these terms. My special thanks go to Jamie Honan for defining the initial bootrom specifications, to Markus Gutschke for enhancing mknbi-linux, and to Jens-Uwe Mager for explaining to me the basics of the NFS networking system and sometimes helping me out with his wealth of knowledge and experience. 8.2.2. Overview Booting a computer without a hard disk usually requires a floppy disk drive or a network connection in order to get the operating system into the RAM and up running. This package allows a diskless PC to boot an operating system using an IP based ethernet network. This is done in the following steps: · First the operating system has to be loaded into system memory. This can be done using a bootrom, which loads the operating system image over the network. The bootrom code found in this package can be burned into a real EPROM, or just copied onto a floppy and then started from it upon bootup. Please note that the term bootrom in all documentation texts in this package refers to the real EPROM version as well as the version copied onto and started from a floppy disk. For the bootrom to find the kernel image it uses the BOOTP protocol as defined in ``'' and ``'' to get the necessary boot information, and then loads the actual image using the TFTP protocol as defined in ``''. · When the operating system starts running, it has to setup it's memory layout using a special boot loader, which is included into the boot image. Then it has to mount it's root filesystem. This can either be done using NFS over the network, or using a ramdisk. The exact specifications for this netboot process can be found here . 8.2.3. Features Booting a diskless client either from an EPROM or from a floppy without additional utility tools The Bootrom code can use many standard DOS packet drivers and therefore supports almost any PC network card. Easy configuration of the bootrom under UNIX. The bootrom can load a BOOTP vendor extension file in order to support more space for tags according to ``''. Using the bootrom menu support it's possible to optionally boot different operating systems. Even if there is a hard disk installed in the client computer, the bootrom can be used as a boot manager, since it also allows booting from any partition. Cross-gateway booting Bootrom runs on any 80x86 processor but is optimized for the 386+. Able to boot different operating system. Currently supported are Linux and MS-DOS. 8.2.4. Installation See the file ``'' for installation instructions. If you have any problems installing or running the programs see the file ``''. 8.2.5. Mailing list There exists a mailing list devoted to network booting. To subscribe simply send a mail with the line subscribe netboot in it's body to majordomo@baghira.han.de The subject in the mail header doesn't matter. This mailing list is intended to be a general discussion forum about any aspect of network booting. Any new versions of this Netboot package will also get announced on that mailing list. After subscribing to it, you can send messages into the list by writing a mail to netboot@baghira.han.de. 8.2.6. Disclaimer The software in this package heavily interacts with hardware and software not only on the local system, but also on the boot server. Use it at your own risk. I cannot be held responsible for any damage done by this software. 8.3. Download Netboot You can download netboot version 0.9 from and netboot version 0.8.1 from 8.4. Netboot useful links Netboot mailing list archive is at · 3com drivers at · Accton drivers at here · Artisoft · CNET · Compaq · D-Link · Microdyne · Many NE2000 PCI cards are based on Realtek chipsets. Get drivers here · Standard Microsystems Corp · Surecom · Thomas Conrad corp · Winbond · Xircom · Webopaedia page on network cards · Jargon's driver page with many drivers for older network cards. · Etherboot This is a project similar to Netbot but based on the BSD bootrom code. · How to make an X Window Terminal out of your old or outdated PC. · List of jumper settings for various network cards. This page also contains many other good links. · Freefire is the home page of the Freefire project, which lists many resources for network security issues. 8.5. RFC 951 Network Working Group Bill Croft (Stanford University) Request for Comments: 951 John Gilmore (Sun Microsystems) September 1985 BOOTSTRAP PROTOCOL (BOOTP) 1. Status of this Memo This RFC suggests a proposed protocol for the ARPA-Internet community, and requests discussion and suggestions for improvements. Distribution of this memo is unlimited. 2. Overview This RFC describes an IP/UDP bootstrap protocol (BOOTP) which allows a diskless client machine to discover its own IP address, the address of a server host, and the name of a file to be loaded into memory and executed. The bootstrap operation can be thought of as consisting of TWO PHASES. This RFC describes the first phase, which could be labeled 'address determination and bootfile selection'. After this address and filename information is obtained, control passes to the second phase of the bootstrap where a file transfer occurs. The file transfer will typically use the TFTP protocol [9], since it is intended that both phases reside in PROM on the client. However BOOTP could also work with other protocols such as SFTP [3] or FTP [6]. We suggest that the client's PROM software provide a way to do a complete bootstrap without 'user' interaction. This is the type of boot that would occur during an unattended power-up. A mechanism should be provided for the user to manually supply the necessary address and filename information to bypass the BOOTP protocol and enter the file transfer phase directly. If non-volatile storage is available, we suggest keeping default settings there and bypassing the BOOTP protocol unless these settings cause the file transfer phase to fail. If the cached information fails, the bootstrap should fall back to phase 1 and use BOOTP. Here is a brief outline of the protocol: 1. A single packet exchange is performed. Timeouts are used to retransmit until a reply is received. The same packet field layout is used in both directions. Fixed length fields of maximum reasonable length are used to simplify structure definition and parsing. 2. An 'opcode' field exists with two values. The client broadcasts a 'bootrequest' packet. The server then answers with a 'bootreply' packet. The bootrequest contains the client's hardware address and its IP address, if known. Croft & Gilmore [Page 1] RFC 951 September 1985 Bootstrap Protocol 3. The request can optionally contain the name of the server the client wishes to respond. This is so the client can force the boot to occur from a specific host (e.g. if multiple versions of the same bootfile exist or if the server is in a far distant net/domain). The client does not have to deal with name / domain services; instead this function is pushed off to the BOOTP server. 4. The request can optionally contain the 'generic' filename to be booted. For example 'unix' or 'ethertip'. When the server sends the bootreply, it replaces this field with the fully qualified path name of the appropriate boot file. In determining this name, the server may consult his own database correlating the client's address and filename request, with a particular boot file customized for that client. If the bootrequest filename is a null string, then the server returns a filename field indicating the 'default' file to be loaded for that client. 5. In the case of clients who do not know their IP addresses, the server must also have a database relating hardware address to IP address. This client IP address is then placed into a field in the bootreply. 6. Certain network topologies (such as Stanford's) may be such that a given physical cable does not have a TFTP server directly attached to it (e.g. all the gateways and hosts on a certain cable may be diskless). With the cooperation of neighboring gateways, BOOTP can allow clients to boot off of servers several hops away, through these gateways. See the section 'Booting Through Gateways' below. This part of the protocol requires no special action on the part of the client. Implementation is optional and requires a small amount of additional code in gateways and servers. 3. Packet Format All numbers shown are decimal, unless indicated otherwise. The BOOTP packet is enclosed in a standard IP [8] UDP [7] datagram. For simplicity it is assumed that the BOOTP packet is never fragmented. Any numeric fields shown are packed in 'standard network byte order', i.e. high order bits are sent first. In the IP header of a bootrequest, the client fills in its own IP source address if known, otherwise zero. When the server address is unknown, the IP destination address will be the 'broadcast address' 255.255.255.255. This address means 'broadcast on the local cable, (I don't know my net number)' [4]. Croft & Gilmore [Page 2] RFC 951 September 1985 Bootstrap Protocol The UDP header contains source and destination port numbers. The BOOTP protocol uses two reserved port numbers, 'BOOTP client' (68) and 'BOOTP server' (67). The client sends requests using 'BOOTP server' as the destination port; this is usually a broadcast. The server sends replies using 'BOOTP client' as the destination port; depending on the kernel or driver facilities in the server, this may or may not be a broadcast (this is explained further in the section titled 'Chicken/Egg issues' below). The reason TWO reserved ports are used, is to avoid 'waking up' and scheduling the BOOTP server daemons, when a bootreply must be broadcast to a client. Since the server and other hosts won't be listening on the 'BOOTP client' port, any such incoming broadcasts will be filtered out at the kernel level. We could not simply allow the client to pick a 'random' port number for the UDP source port field; since the server reply may be broadcast, a randomly chosen port number could confuse other hosts that happened to be listening on that port. The UDP length field is set to the length of the UDP plus BOOTP portions of the packet. The UDP checksum field can be set to zero by the client (or server) if desired, to avoid this extra overhead in a PROM implementation. In the 'Packet Processing' section below the phrase '[UDP checksum.]' is used whenever the checksum might be verified/computed. FIELD BYTES DESCRIPTION ----- ----- ----------- op 1 packet op code / message type. 1 = BOOTREQUEST, 2 = BOOTREPLY htype 1 hardware address type, see ARP section in "Assigned Numbers" RFC. '1' = 10mb ethernet hlen 1 hardware address length (eg '6' for 10mb ethernet). hops 1 client sets to zero, optionally used by gateways in cross-gateway booting. xid 4 transaction ID, a random number, used to match this boot request with the responses it generates. secs 2 filled in by client, seconds elapsed since client started trying to boot. Croft & Gilmore [Page 3] RFC 951 September 1985 Bootstrap Protocol -- 2 unused ciaddr 4 client IP address; filled in by client in bootrequest if known. yiaddr 4 'your' (client) IP address; filled by server if client doesn't know its own address (ciaddr was 0). siaddr 4 server IP address; returned in bootreply by server. giaddr 4 gateway IP address, used in optional cross-gateway booting. chaddr 16 client hardware address, filled in by client. sname 64 optional server host name, null terminated string. file 128 boot file name, null terminated string; 'generic' name or null in bootrequest, fully qualified directory-path name in bootreply. vend 64 optional vendor-specific area, e.g. could be hardware type/serial on request, or 'capability' / remote file system handle on reply. This info may be set aside for use by a third phase bootstrap or kernel. 4. Chicken / Egg Issues How can the server send an IP datagram to the client, if the client doesnt know its own IP address (yet)? Whenever a bootreply is being sent, the transmitting machine performs the following operations: 1. If the client knows its own IP address ('ciaddr' field is nonzero), then the IP can be sent 'as normal', since the client will respond to ARPs [5]. 2. If the client does not yet know its IP address (ciaddr zero), then the client cannot respond to ARPs sent by the transmitter of the bootreply. There are two options: a. If the transmitter has the necessary kernel or driver hooks Croft & Gilmore [Page 4] RFC 951 September 1985 Bootstrap Protocol to 'manually' construct an ARP address cache entry, then it can fill in an entry using the 'chaddr' and 'yiaddr' fields. Of course, this entry should have a timeout on it, just like any other entry made by the normal ARP code itself. The transmitter of the bootreply can then simply send the bootreply to the client's IP address. UNIX (4.2 BSD) has this capability. b. If the transmitter lacks these kernel hooks, it can simply send the bootreply to the IP broadcast address on the appropriate interface. This is only one additional broadcast over the previous case. 5. Client Use of ARP The client PROM must contain a simple implementation of ARP, e.g. the address cache could be just one entry in size. This will allow a second-phase-only boot (TFTP) to be performed when the client knows the IP addresses and bootfile name. Any time the client is expecting to receive a TFTP or BOOTP reply, it should be prepared to answer an ARP request for its own IP to hardware address mapping (if known). Since the bootreply will contain (in the hardware encapsulation) the hardware source address of the server/gateway, the client MAY be able to avoid sending an ARP request for the server/gateway IP address to be used in the following TFTP phase. However this should be treated only as a special case, since it is desirable to still allow a second-phase-only boot as described above. 6. Comparison to RARP An earlier protocol, Reverse Address Resolution Protocol (RARP) [1] was proposed to allow a client to determine its IP address, given that it knew its hardware address. However RARP had the disadvantage that it was a hardware link level protocol (not IP/UDP based). This means that RARP could only be implemented on hosts containing special kernel or driver modifications to access these 'raw' packets. Since there are many network kernels existent now, with each source maintained by different organizations, a boot protocol that does not require kernel modifications is a decided advantage. BOOTP provides this hardware to IP address lookup function, in addition to the other useful features described in the sections above. Croft & Gilmore [Page 5] RFC 951 September 1985 Bootstrap Protocol 7. Packet Processing 7.1. Client Transmission Before setting up the packet for the first time, it is a good idea to clear the entire packet buffer to all zeros; this will place all fields in their default state. The client then creates a packet with the following fields. The IP destination address is set to 255.255.255.255. (the broadcast address) or to the server's IP address (if known). The IP source address and 'ciaddr' are set to the client's IP address if known, else 0. The UDP header is set with the proper length; source port = 'BOOTP client' port destination port = 'BOOTP server' port. 'op' is set to '1', BOOTREQUEST. 'htype' is set to the hardware address type as assigned in the ARP section of the "Assigned Numbers" RFC. 'hlen' is set to the length of the hardware address, e.g. '6' for 10mb ethernet. 'xid' is set to a 'random' transaction id. 'secs' is set to the number of seconds that have elapsed since the client has started booting. This will let the servers know how long a client has been trying. As the number gets larger, certain servers may feel more 'sympathetic' towards a client they don't normally service. If a client lacks a suitable clock, it could construct a rough estimate using a loop timer. Or it could choose to simply send this field as always a fixed value, say 100 seconds. If the client knows its IP address, 'ciaddr' (and the IP source address) are set to this value. 'chaddr' is filled in with the client's hardware address. If the client wishes to restrict booting to a particular server name, it may place a null-terminated string in 'sname'. The name used should be any of the allowable names or nicknames of the desired host. The client has several options for filling the 'file' name field. If left null, the meaning is 'I want to boot the default file for my machine'. A null file name can also mean 'I am only interested in finding out client/server/gateway IP addresses, I dont care about file names'. The field can also be a 'generic' name such as 'unix' or Croft & Gilmore [Page 6] RFC 951 September 1985 Bootstrap Protocol 'gateway'; this means 'boot the named program configured for my machine'. Finally the field can be a fully directory qualified path name. The 'vend' field can be filled in by the client with vendor-specific strings or structures. For example the machine hardware type or serial number may be placed here. However the operation of the BOOTP server should not DEPEND on this information existing. If the 'vend' field is used, it is recommended that a 4 byte 'magic number' be the first item within 'vend'. This lets a server determine what kind of information it is seeing in this field. Numbers can be assigned by the usual 'magic number' process --you pick one and it's magic. A different magic number could be used for bootreply's than bootrequest's to allow the client to take special action with the reply information. [UDP checksum.] 7.2. Client Retransmission Strategy If no reply is received for a certain length of time, the client should retransmit the request. The time interval must be chosen carefully so as not to flood the network. Consider the case of a cable containing 100 machines that are just coming up after a power failure. Simply retransmitting the request every four seconds will inundate the net. As a possible strategy, you might consider backing off exponentially, similar to the way ethernet backs off on a collision. So for example if the first packet is at time 0:00, the second would be at :04, then :08, then :16, then :32, then :64. You should also randomize each time; this would be done similar to the ethernet specification by starting with a mask and 'and'ing that with with a random number to get the first backoff. On each succeeding backoff, the mask is increased in length by one bit. This doubles the average delay on each backoff. After the 'average' backoff reaches about 60 seconds, it should be increased no further, but still randomized. Before each retransmission, the client should update the 'secs' field. [UDP checksum.] Croft & Gilmore [Page 7] RFC 951 September 1985 Bootstrap Protocol 7.3. Server Receives BOOTREQUEST [UDP checksum.] If the UDP destination port does not match the 'BOOTP server' port, discard the packet. If the server name field (sname) is null (no particular server specified), or sname is specified and matches our name or nickname, then continue with packet processing. If the sname field is specified, but does not match 'us', then there are several options: 1. You may choose to simply discard this packet. 2. If a name lookup on sname shows it to be on this same cable, discard the packet. 3. If sname is on a different net, you may choose to forward the packet to that address. If so, check the 'giaddr' (gateway address) field. If 'giaddr' is zero, fill it in with my address or the address of a gateway that can be used to get to that net. Then forward the packet. If the client IP address (ciaddr) is zero, then the client does not know its own IP address. Attempt to lookup the client hardware address (chaddr, hlen, htype) in our database. If no match is found, discard the packet. Otherwise we now have an IP address for this client; fill it into the 'yiaddr' (your IP address) field. We now check the boot file name field (file). The field will be null if the client is not interested in filenames, or wants the default bootfile. If the field is non-null, it is used as a lookup key in a database, along with the client's IP address. If there is a default file or generic file (possibly indexed by the client address) or a fully-specified path name that matches, then replace the 'file' field with the fully-specified path name of the selected boot file. If the field is non-null and no match was found, then the client is asking for a file we dont have; discard the packet, perhaps some other BOOTP server will have it. The 'vend' vendor-specific data field should now be checked and if a recognized type of data is provided, client-specific actions should be taken, and a response placed in the 'vend' data field of the reply packet. For example, a workstation client could provide Croft & Gilmore [Page 8] RFC 951 September 1985 Bootstrap Protocol an authentication key and receive from the server a capability for remote file access, or a set of configuration options, which can be passed to the operating system that will shortly be booted in. Place my (server) IP address in the 'siaddr' field. Set the 'op' field to BOOTREPLY. The UDP destination port is set to 'BOOTP client'. If the client address 'ciaddr' is nonzero, send the packet there; else if the gateway address 'giaddr' is nonzero, set the UDP destination port to 'BOOTP server' and send the packet to 'giaddr'; else the client is on one of our cables but it doesnt know its own IP address yet --use a method described in the 'Egg' section above to send it to the client. If 'Egg' is used and we have multiple interfaces on this host, use the 'yiaddr' (your IP address) field to figure out which net (cable/interface) to send the packet to. [UDP checksum.] 7.4. Server/Gateway Receives BOOTREPLY [UDP checksum.] If 'yiaddr' (your [the client's] IP address) refers to one of our cables, use one of the 'Egg' methods above to forward it to the client. Be sure to send it to the 'BOOTP client' UDP destination port. 7.5. Client Reception Don't forget to process ARP requests for my own IP address (if I know it). [UDP checksum.] The client should discard incoming packets that: are not IP/UDPs addressed to the boot port; are not BOOTREPLYs; do not match my IP address (if I know it) or my hardware address; do not match my transaction id. Otherwise we have received a successful reply. 'yiaddr' will contain my IP address, if I didnt know it before. 'file' is the name of the file name to TFTP 'read request'. The server address is in 'siaddr'. If 'giaddr' (gateway address) is nonzero, then the packets should be forwarded there first, in order to get to the server. 8. Booting Through Gateways This part of the protocol is optional and requires some additional code in cooperating gateways and servers, but it allows cross-gateway booting. This is mainly useful when gateways are diskless machines. Gateways containing disks (e.g. a UNIX machine acting as a gateway), might as well run their own BOOTP/TFTP servers. Gateways listening to broadcast BOOTREQUESTs may decide to forward or rebroadcast these requests 'when appropriate'. For example, the Croft & Gilmore [Page 9] RFC 951 September 1985 Bootstrap Protocol gateway could have, as part of his configuration tables, a list of other networks or hosts to receive a copy of any broadcast BOOTREQUESTs. Even though a 'hops' field exists, it is a poor idea to simply globally rebroadcast the requests, since broadcast loops will almost certainly occur. The forwarding could begin immediately, or wait until the 'secs' (seconds client has been trying) field passes a certain threshold. If a gateway does decide to forward the request, it should look at the 'giaddr' (gateway IP address) field. If zero, it should plug its own IP address (on the receiving cable) into this field. It may also use the 'hops' field to optionally control how far the packet is reforwarded. Hops should be incremented on each forwarding. For example, if hops passes '3', the packet should probably be discarded. [UDP checksum.] Here we have recommended placing this special forwarding function in the gateways. But that does not have to be the case. As long as some 'BOOTP forwarding agent' exists on the net with the booting client, the agent can do the forwarding when appropriate. Thus this service may or may not be co-located with the gateway. In the case of a forwarding agent not located in the gateway, the agent could save himself some work by plugging the broadcast address of the interface receiving the bootrequest into the 'giaddr' field. Thus the reply would get forwarded using normal gateways, not involving the forwarding agent. Of course the disadvantage here is that you lose the ability to use the 'Egg' non-broadcast method of sending the reply, causing extra overhead for every host on the client cable. 9. Sample BOOTP Server Database As a suggestion, we show a sample text file database that the BOOTP server program might use. The database has two sections, delimited by a line containing an percent in column 1. The first section contains a 'default directory' and mappings from generic names to directory/pathnames. The first generic name in this section is the 'default file' you get when the bootrequest contains a null 'file' string. The second section maps hardware addresstype/address into an ipaddress. Optionally you can also overide the default generic name by supplying a ipaddress specific genericname. A 'suffix' item is also an option; if supplied, any generic names specified by the client will be accessed by first appending 'suffix' to the 'pathname' Croft & Gilmore [Page 10] RFC 951 September 1985 Bootstrap Protocol appropriate to that generic name. If that file is not found, then the plain 'pathname' will be tried. This 'suffix' option allows a whole set of custom generics to be setup without a lot of effort. Below is shown the general format; fields are delimited by one or more spaces or tabs; trailing empty fields may be omitted; blank lines and lines beginning with '#' are ignored. # comment line homedirectory genericname1 pathname1 genericname2 pathname2 ... % end of generic names, start of address mappings hostname1 hardwaretype hardwareaddr1 ipaddr1 genericname suffix hostname2 hardwaretype hardwareaddr2 ipaddr2 genericname suffix ... Here is a specific example. Note the 'hardwaretype' number is the same as that shown in the ARP section of the 'Assigned Numbers' RFC. The 'hardwaretype' and 'ipaddr' numbers are in decimal; 'hardwareaddr' is in hex. # last updated by smith /usr/boot vmunix vmunix tip ethertip watch /usr/diag/etherwatch gate gate. % end of generic names, start of address mappings hamilton 1 02.60.8c.06.34.98 36.19.0.5 burr 1 02.60.8c.34.11.78 36.44.0.12 101-gateway 1 02.60.8c.23.ab.35 36.44.0.32 gate 101 mjh-gateway 1 02.60.8c.12.32.bc 36.42.0.64 gate mjh welch-tipa 1 02.60.8c.22.65.32 36.47.0.14 tip welch-tipb 1 02.60.8c.12.15.c8 36.46.0.12 tip In the example above, if 'mjh-gateway' does a default boot, it will get the file '/usr/boot/gate.mjh'. Croft & Gilmore [Page 11] RFC 951 September 1985 Bootstrap Protocol 10. Acknowledgements Ross Finlayson (et. al.) produced two earlier RFC's discussing TFTP bootstraping [2] using RARP [1]. We would also like to acknowledge the previous work and comments of Noel Chiappa, Bob Lyon, Jeff Mogul, Mark Lewis, and David Plummer. REFERENCES 1. Ross Finlayson, Timothy Mann, Jeffrey Mogul, Marvin Theimer. A Reverse Address Resolution Protocol. RFC 903, NIC, June, 1984. 2. Ross Finlayson. Bootstrap Loading using TFTP. RFC 906, NIC, June, 1984. 3. Mark Lottor. Simple File Transfer Protocol. RFC 913, NIC, September, 1984. 4. Jeffrey Mogul. Broadcasting Internet Packets. RFC 919, NIC, October, 1984. 5. David Plummer. An Ethernet Address Resolution Protocol. RFC 826, NIC, September, 1982. 6. Jon Postel. File Transfer Protocol. RFC 765, NIC, June, 1980. 7. Jon Postel. User Datagram Protocol. RFC 768, NIC, August, 1980. 8. Jon Postel. Internet Protocol. RFC 791, NIC, September, 1981. 9. K. R. Sollins, Noel Chiappa. The TFTP Protocol. RFC 783, NIC, June, 1981. Croft & Gilmore [Page 12] 8.6. RFC 1533 Network Working Group S. Alexander Request for Comments: 1533 Lachman Technology, Inc. Obsoletes: 1497, 1395, 1084, 1048 R. Droms Category: Standards Track Bucknell University October 1993 DHCP Options and BOOTP Vendor Extensions Status of this Memo This RFC specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited. Abstract The Dynamic Host Configuration Protocol (DHCP) [1] provides a framework for passing configuration information to hosts on a TCP/IP network. Configuration parameters and other control information are carried in tagged data items that are stored in the "options" field of the DHCP message. The data items themselves are also called "options." This document specifies the current set of DHCP options. This document will be periodically updated as new options are defined. Each superseding document will include the entire current list of valid options. All of the vendor information extensions defined in RFC 1497 [2] may be used as DHCP options. The definitions given in RFC 1497 are included in this document, which supersedes RFC 1497. All of the DHCP options defined in this document, except for those specific to DHCP as defined in section 9, may be used as BOOTP vendor information extensions. Table of Contents 1. Introduction .............................................. 2 2. BOOTP Extension/DHCP Option Field Format .................. 2 3. RFC 1497 Vendor Extensions ................................ 3 4. IP Layer Parameters per Host .............................. 10 5. IP Layer Parameters per Interface ........................ 13 6. Link Layer Parameters per Interface ....................... 16 7. TCP Parameters ............................................ 17 8. Application and Service Parameters ........................ 18 Alexander & Droms [Page 1] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 9. DHCP Extensions ........................................... 23 10. Extensions ................................................ 27 11. Acknowledgements .......................................... 28 12. References ................................................ 28 13. Security Considerations ................................... 19 14. Authors' Addresses ........................................ 30 1. Introduction This document specifies options for use with both the Dynamic Host Configuration Protocol and the Bootstrap Protocol. The full description of DHCP packet formats may be found in the DHCP specification document [1], and the full description of BOOTP packet formats may be found in the BOOTP specification document [3]. This document defines the format of information in the last field of DHCP packets ('options') and of BOOTP packets ('vend'). The remainder of this section defines a generalized use of this area for giving information useful to a wide class of machines, operating systems and configurations. Sites with a single DHCP or BOOTP server that is shared among heterogeneous clients may choose to define other, site- specific formats for the use of the 'options' field. Section 2 of this memo describes the formats of DHCP options and BOOTP vendor extensions. Section 3 describes options defined in previous documents for use with BOOTP (all may also be used with DHCP). Sections 4-8 define new options intended for use with both DHCP and BOOTP. Section 9 defines options used only in DHCP. References further describing most of the options defined in sections 2-6 can be found in section 12. The use of the options defined in section 9 is described in the DHCP specification [1]. Information on registering new options is contained in section 10. 2. BOOTP Extension/DHCP Option Field Format DHCP options have the same format as the BOOTP "vendor extensions" defined in RFC 1497 [2]. Options may be fixed length or variable length. All options begin with a tag octet, which uniquely identifies the option. Fixed-length options without data consist of only a tag octet. Only options 0 and 255 are fixed length. All other options are variable-length with a length octet following the tag octet. The value of the length octet does not include the two octets specifying the tag and length. The length octet is followed by "length" octets of data. In the case of some variable-length options the length field is a constant but must still be specified. Alexander & Droms [Page 2] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 Any options defined subsequent to this document should contain a length octet even if the length is fixed or zero. All multi-octet quantities are in network byte-order. When used with BOOTP, the first four octets of the vendor information field have been assigned to the "magic cookie" (as suggested in RFC 951). This field identifies the mode in which the succeeding data is to be interpreted. The value of the magic cookie is the 4 octet dotted decimal 99.130.83.99 (or hexadecimal number 63.82.53.63) in network byte order. All of the "vendor extensions" defined in RFC 1497 are also DHCP options. Option codes 128 to 254 (decimal) are reserved for site-specific options. Except for the options in section 9, all options may be used with either DHCP or BOOTP. Many of these options have their default values specified in other documents. In particular, RFC 1122 [4] specifies default values for most IP and TCP configuration parameters. 3. RFC 1497 Vendor Extensions This section lists the vendor extensions as defined in RFC 1497. They are defined here for completeness. 3.1. Pad Option The pad option can be used to cause subsequent fields to align on word boundaries. The code for the pad option is 0, and its length is 1 octet. Code +-----+ | 0 | +-----+ Alexander & Droms [Page 3] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 3.2. End Option The end option marks the end of valid information in the vendor field. Subsequent octets should be filled with pad options. The code for the end option is 255, and its length is 1 octet. Code +-----+ | 255 | +-----+ 3.3. Subnet Mask The subnet mask option specifies the client's subnet mask as per RFC 950 [5]. If both the subnet mask and the router option are specified in a DHCP reply, the subnet mask option MUST be first. The code for the subnet mask option is 1, and its length is 4 octets. Code Len Subnet Mask +-----+-----+-----+-----+-----+-----+ | 1 | 4 | m1 | m2 | m3 | m4 | +-----+-----+-----+-----+-----+-----+ 3.4. Time Offset The time offset field specifies the offset of the client's subnet in seconds from Coordinated Universal Time (UTC). The offset is expressed as a signed 32-bit integer. The code for the time offset option is 2, and its length is 4 octets. Code Len Time Offset +-----+-----+-----+-----+-----+-----+ | 2 | 4 | n1 | n2 | n3 | n4 | +-----+-----+-----+-----+-----+-----+ Alexander & Droms [Page 4] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 3.5. Router Option The router option specifies a list of IP addresses for routers on the client's subnet. Routers SHOULD be listed in order of preference. The code for the router option is 3. The minimum length for the router option is 4 octets, and the length MUST always be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-- | 3 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-- 3.6. Time Server Option The time server option specifies a list of RFC 868 [6] time servers available to the client. Servers SHOULD be listed in order of preference. The code for the time server option is 4. The minimum length for this option is 4 octets, and the length MUST always be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-- | 4 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-- 3.7. Name Server Option The name server option specifies a list of IEN 116 [7] name servers available to the client. Servers SHOULD be listed in order of preference. The code for the name server option is 5. The minimum length for this option is 4 octets, and the length MUST always be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-- | 5 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-- Alexander & Droms [Page 5] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 3.8. Domain Name Server Option The domain name server option specifies a list of Domain Name System (STD 13, RFC 1035 [8]) name servers available to the client. Servers SHOULD be listed in order of preference. The code for the domain name server option is 6. The minimum length for this option is 4 octets, and the length MUST always be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-- | 6 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-- 3.9. Log Server Option The log server option specifies a list of MIT-LCS UDP log servers available to the client. Servers SHOULD be listed in order of preference. The code for the log server option is 7. The minimum length for this option is 4 octets, and the length MUST always be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-- | 7 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-- 3.10. Cookie Server Option The cookie server option specifies a list of RFC 865 [9] cookie servers available to the client. Servers SHOULD be listed in order of preference. The code for the log server option is 8. The minimum length for this option is 4 octets, and the length MUST always be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-- | 8 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-- Alexander & Droms [Page 6] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 3.11. LPR Server Option The LPR server option specifies a list of RFC 1179 [10] line printer servers available to the client. Servers SHOULD be listed in order of preference. The code for the LPR server option is 9. The minimum length for this option is 4 octets, and the length MUST always be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-- | 9 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-- 3.12. Impress Server Option The Impress server option specifies a list of Imagen Impress servers available to the client. Servers SHOULD be listed in order of preference. The code for the Impress server option is 10. The minimum length for this option is 4 octets, and the length MUST always be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-- | 10 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-- 3.13. Resource Location Server Option This option specifies a list of RFC 887 [11] Resource Location servers available to the client. Servers SHOULD be listed in order of preference. The code for this option is 11. The minimum length for this option is 4 octets, and the length MUST always be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-- | 11 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-- Alexander & Droms [Page 7] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 3.14. Host Name Option This option specifies the name of the client. The name may or may not be qualified with the local domain name (see section 3.17 for the preferred way to retrieve the domain name). See RFC 1035 for character set restrictions. The code for this option is 12, and its minimum length is 1. Code Len Host Name +-----+-----+-----+-----+-----+-----+-----+-----+-- | 12 | n | h1 | h2 | h3 | h4 | h5 | h6 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-- 3.15. Boot File Size Option This option specifies the length in 512-octet blocks of the default boot image for the client. The file length is specified as an unsigned 16-bit integer. The code for this option is 13, and its length is 2. Code Len File Size +-----+-----+-----+-----+ | 13 | 2 | l1 | l2 | +-----+-----+-----+-----+ 3.16. Merit Dump File This option specifies the path-name of a file to which the client's core image should be dumped in the event the client crashes. The path is formatted as a character string consisting of characters from the NVT ASCII character set. The code for this option is 14. Its minimum length is 1. Code Len Dump File Pathname +-----+-----+-----+-----+-----+-----+--- | 14 | n | n1 | n2 | n3 | n4 | ... +-----+-----+-----+-----+-----+-----+--- Alexander & Droms [Page 8] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 3.17. Domain Name This option specifies the domain name that client should use when resolving hostnames via the Domain Name System. The code for this option is 15. Its minimum length is 1. Code Len Domain Name +-----+-----+-----+-----+-----+-----+-- | 15 | n | d1 | d2 | d3 | d4 | ... +-----+-----+-----+-----+-----+-----+-- 3.18. Swap Server This specifies the IP address of the client's swap server. The code for this option is 16 and its length is 4. Code Len Swap Server Address +-----+-----+-----+-----+-----+-----+ | 16 | n | a1 | a2 | a3 | a4 | +-----+-----+-----+-----+-----+-----+ 3.19. Root Path This option specifies the path-name that contains the client's root disk. The path is formatted as a character string consisting of characters from the NVT ASCII character set. The code for this option is 17. Its minimum length is 1. Code Len Root Disk Pathname +-----+-----+-----+-----+-----+-----+--- | 17 | n | n1 | n2 | n3 | n4 | ... +-----+-----+-----+-----+-----+-----+--- Alexander & Droms [Page 9] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 3.20. Extensions Path A string to specify a file, retrievable via TFTP, which contains information which can be interpreted in the same way as the 64-octet vendor-extension field within the BOOTP response, with the following exceptions: - the length of the file is unconstrained; - all references to Tag 18 (i.e., instances of the BOOTP Extensions Path field) within the file are ignored. The code for this option is 18. Its minimum length is 1. Code Len Extensions Pathname +-----+-----+-----+-----+-----+-----+--- | 18 | n | n1 | n2 | n3 | n4 | ... +-----+-----+-----+-----+-----+-----+--- 4. IP Layer Parameters per Host This section details the options that affect the operation of the IP layer on a per-host basis. 4.1. IP Forwarding Enable/Disable Option This option specifies whether the client should configure its IP layer for packet forwarding. A value of 0 means disable IP forwarding, and a value of 1 means enable IP forwarding. The code for this option is 19, and its length is 1. Code Len Value +-----+-----+-----+ | 19 | 1 | 0/1 | +-----+-----+-----+ Alexander & Droms [Page 10] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 4.2. Non-Local Source Routing Enable/Disable Option This option specifies whether the client should configure its IP layer to allow forwarding of datagrams with non-local source routes (see Section 3.3.5 of [4] for a discussion of this topic). A value of 0 means disallow forwarding of such datagrams, and a value of 1 means allow forwarding. The code for this option is 20, and its length is 1. Code Len Value +-----+-----+-----+ | 20 | 1 | 0/1 | +-----+-----+-----+ 4.3. Policy Filter Option This option specifies policy filters for non-local source routing. The filters consist of a list of IP addresses and masks which specify destination/mask pairs with which to filter incoming source routes. Any source routed datagram whose next-hop address does not match one of the filters should be discarded by the client. See [4] for further information. The code for this option is 21. The minimum length of this option is 8, and the length MUST be a multiple of 8. Code Len Address 1 Mask 1 +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+ | 21 | n | a1 | a2 | a3 | a4 | m1 | m2 | m3 | m4 | +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+ Address 2 Mask 2 +-----+-----+-----+-----+-----+-----+-----+-----+--- | a1 | a2 | a3 | a4 | m1 | m2 | m3 | m4 | ... +-----+-----+-----+-----+-----+-----+-----+-----+--- Alexander & Droms [Page 11] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 4.4. Maximum Datagram Reassembly Size This option specifies the maximum size datagram that the client should be prepared to reassemble. The size is specified as a 16-bit unsigned integer. The minimum value legal value is 576. The code for this option is 22, and its length is 2. Code Len Size +-----+-----+-----+-----+ | 22 | 2 | s1 | s2 | +-----+-----+-----+-----+ 4.5. Default IP Time-to-live This option specifies the default time-to-live that the client should use on outgoing datagrams. The TTL is specified as an octet with a value between 1 and 255. The code for this option is 23, and its length is 1. Code Len TTL +-----+-----+-----+ | 23 | 1 | ttl | +-----+-----+-----+ 4.6. Path MTU Aging Timeout Option This option specifies the timeout (in seconds) to use when aging Path MTU values discovered by the mechanism defined in RFC 1191 [12]. The timeout is specified as a 32-bit unsigned integer. The code for this option is 24, and its length is 4. Code Len Timeout +-----+-----+-----+-----+-----+-----+ | 24 | 4 | t1 | t2 | t3 | t4 | +-----+-----+-----+-----+-----+-----+ Alexander & Droms [Page 12] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 4.7. Path MTU Plateau Table Option This option specifies a table of MTU sizes to use when performing Path MTU Discovery as defined in RFC 1191. The table is formatted as a list of 16-bit unsigned integers, ordered from smallest to largest. The minimum MTU value cannot be smaller than 68. The code for this option is 25. Its minimum length is 2, and the length MUST be a multiple of 2. Code Len Size 1 Size 2 +-----+-----+-----+-----+-----+-----+--- | 25 | n | s1 | s2 | s1 | s2 | ... +-----+-----+-----+-----+-----+-----+--- 5. IP Layer Parameters per Interface This section details the options that affect the operation of the IP layer on a per-interface basis. It is expected that a client can issue multiple requests, one per interface, in order to configure interfaces with their specific parameters. 5.1. Interface MTU Option This option specifies the MTU to use on this interface. The MTU is specified as a 16-bit unsigned integer. The minimum legal value for the MTU is 68. The code for this option is 26, and its length is 2. Code Len MTU +-----+-----+-----+-----+ | 26 | 2 | m1 | m2 | +-----+-----+-----+-----+ Alexander & Droms [Page 13] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 5.2. All Subnets are Local Option This option specifies whether or not the client may assume that all subnets of the IP network to which the client is connected use the same MTU as the subnet of that network to which the client is directly connected. A value of 1 indicates that all subnets share the same MTU. A value of 0 means that the client should assume that some subnets of the directly connected network may have smaller MTUs. The code for this option is 27, and its length is 1. Code Len Value +-----+-----+-----+ | 27 | 1 | 0/1 | +-----+-----+-----+ 5.3. Broadcast Address Option This option specifies the broadcast address in use on the client's subnet. Legal values for broadcast addresses are specified in section 3.2.1.3 of [4]. The code for this option is 28, and its length is 4. Code Len Broadcast Address +-----+-----+-----+-----+-----+-----+ | 28 | 4 | b1 | b2 | b3 | b4 | +-----+-----+-----+-----+-----+-----+ 5.4. Perform Mask Discovery Option This option specifies whether or not the client should perform subnet mask discovery using ICMP. A value of 0 indicates that the client should not perform mask discovery. A value of 1 means that the client should perform mask discovery. The code for this option is 29, and its length is 1. Code Len Value +-----+-----+-----+ | 29 | 1 | 0/1 | +-----+-----+-----+ Alexander & Droms [Page 14] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 5.5. Mask Supplier Option This option specifies whether or not the client should respond to subnet mask requests using ICMP. A value of 0 indicates that the client should not respond. A value of 1 means that the client should respond. The code for this option is 30, and its length is 1. Code Len Value +-----+-----+-----+ | 30 | 1 | 0/1 | +-----+-----+-----+ 5.6. Perform Router Discovery Option This option specifies whether or not the client should solicit routers using the Router Discovery mechanism defined in RFC 1256 [13]. A value of 0 indicates that the client should not perform router discovery. A value of 1 means that the client should perform router discovery. The code for this option is 31, and its length is 1. Code Len Value +-----+-----+-----+ | 31 | 1 | 0/1 | +-----+-----+-----+ 5.7. Router Solicitation Address Option This option specifies the address to which the client should transmit router solicitation requests. The code for this option is 32, and its length is 4. Code Len Address +-----+-----+-----+-----+-----+-----+ | 32 | 4 | a1 | a2 | a3 | a4 | +-----+-----+-----+-----+-----+-----+ Alexander & Droms [Page 15] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 5.8. Static Route Option This option specifies a list of static routes that the client should install in its routing cache. If multiple routes to the same destination are specified, they are listed in descending order of priority. The routes consist of a list of IP address pairs. The first address is the destination address, and the second address is the router for the destination. The default route (0.0.0.0) is an illegal destination for a static route. See section 3.5 for information about the router option. The code for this option is 33. The minimum length of this option is 8, and the length MUST be a multiple of 8. Code Len Destination 1 Router 1 +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+ | 33 | n | d1 | d2 | d3 | d4 | r1 | r2 | r3 | r4 | +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+ Destination 2 Router 2 +-----+-----+-----+-----+-----+-----+-----+-----+--- | d1 | d2 | d3 | d4 | r1 | r2 | r3 | r4 | ... +-----+-----+-----+-----+-----+-----+-----+-----+--- 6. Link Layer Parameters per Interface This section lists the options that affect the operation of the data link layer on a per-interface basis. 6.1. Trailer Encapsulation Option This option specifies whether or not the client should negotiate the use of trailers (RFC 893 [14]) when using the ARP protocol. A value of 0 indicates that the client should not attempt to use trailers. A value of 1 means that the client should attempt to use trailers. The code for this option is 34, and its length is 1. Code Len Value +-----+-----+-----+ | 34 | 1 | 0/1 | +-----+-----+-----+ Alexander & Droms [Page 16] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 6.2. ARP Cache Timeout Option This option specifies the timeout in seconds for ARP cache entries. The time is specified as a 32-bit unsigned integer. The code for this option is 35, and its length is 4. Code Len Time +-----+-----+-----+-----+-----+-----+ | 35 | 4 | t1 | t2 | t3 | t4 | +-----+-----+-----+-----+-----+-----+ 6.3. Ethernet Encapsulation Option This option specifies whether or not the client should use Ethernet Version 2 (RFC 894 [15]) or IEEE 802.3 (RFC 1042 [16]) encapsulation if the interface is an Ethernet. A value of 0 indicates that the client should use RFC 894 encapsulation. A value of 1 means that the client should use RFC 1042 encapsulation. The code for this option is 36, and its length is 1. Code Len Value +-----+-----+-----+ | 36 | 1 | 0/1 | +-----+-----+-----+ 7. TCP Parameters This section lists the options that affect the operation of the TCP layer on a per-interface basis. 7.1. TCP Default TTL Option This option specifies the default TTL that the client should use when sending TCP segments. The value is represented as an 8-bit unsigned integer. The minimum value is 1. The code for this option is 37, and its length is 1. Code Len TTL +-----+-----+-----+ | 37 | 1 | n | +-----+-----+-----+ Alexander & Droms [Page 17] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 7.2. TCP Keepalive Interval Option This option specifies the interval (in seconds) that the client TCP should wait before sending a keepalive message on a TCP connection. The time is specified as a 32-bit unsigned integer. A value of zero indicates that the client should not generate keepalive messages on connections unless specifically requested by an application. The code for this option is 38, and its length is 4. Code Len Time +-----+-----+-----+-----+-----+-----+ | 38 | 4 | t1 | t2 | t3 | t4 | +-----+-----+-----+-----+-----+-----+ 7.3. TCP Keepalive Garbage Option This option specifies the whether or not the client should send TCP keepalive messages with a octet of garbage for compatibility with older implementations. A value of 0 indicates that a garbage octet should not be sent. A value of 1 indicates that a garbage octet should be sent. The code for this option is 39, and its length is 1. Code Len Value +-----+-----+-----+ | 39 | 1 | 0/1 | +-----+-----+-----+ 8. Application and Service Parameters This section details some miscellaneous options used to configure miscellaneous applications and services. 8.1. Network Information Service Domain Option This option specifies the name of the client's NIS [17] domain. The domain is formatted as a character string consisting of characters from the NVT ASCII character set. The code for this option is 40. Its minimum length is 1. Code Len NIS Domain Name +-----+-----+-----+-----+-----+-----+--- | 40 | n | n1 | n2 | n3 | n4 | ... +-----+-----+-----+-----+-----+-----+--- Alexander & Droms [Page 18] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 8.2. Network Information Servers Option This option specifies a list of IP addresses indicating NIS servers available to the client. Servers SHOULD be listed in order of preference. The code for this option is 41. Its minimum length is 4, and the length MUST be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-- | 41 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-- 8.3. Network Time Protocol Servers Option This option specifies a list of IP addresses indicating NTP [18] servers available to the client. Servers SHOULD be listed in order of preference. The code for this option is 42. Its minimum length is 4, and the length MUST be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-- | 42 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-- 8.4. Vendor Specific Information This option is used by clients and servers to exchange vendor- specific information. The information is an opaque object of n octets, presumably interpreted by vendor-specific code on the clients and servers. The definition of this information is vendor specific. The vendor is indicated in the class-identifier option. Servers not equipped to interpret the vendor-specific information sent by a client MUST ignore it (although it may be reported). Clients which do not receive desired vendor-specific information SHOULD make an attempt to operate without it, although they may do so (and announce they are doing so) in a degraded mode. If a vendor potentially encodes more than one item of information in this option, then the vendor SHOULD encode the option using "Encapsulated vendor-specific options" as described below: The Encapsulated vendor-specific options field SHOULD be encoded as a sequence of code/length/value fields of identical syntax to the DHCP options field with the following exceptions: Alexander & Droms [Page 19] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 1) There SHOULD NOT be a "magic cookie" field in the encapsulated vendor-specific extensions field. 2) Codes other than 0 or 255 MAY be redefined by the vendor within the encapsulated vendor-specific extensions field, but SHOULD conform to the tag-length-value syntax defined in section 2. 3) Code 255 (END), if present, signifies the end of the encapsulated vendor extensions, not the end of the vendor extensions field. If no code 255 is present, then the end of the enclosing vendor-specific information field is taken as the end of the encapsulated vendor-specific extensions field. The code for this option is 43 and its minimum length is 1. Code Len Vendor-specific information +-----+-----+-----+-----+--- | 43 | n | i1 | i2 | ... +-----+-----+-----+-----+--- When encapsulated vendor-specific extensions are used, the information bytes 1-n have the following format: Code Len Data item Code Len Data item Code +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+ | T1 | n | d1 | d2 | ... | T2 | n | D1 | D2 | ... | ... | +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+ 8.5. NetBIOS over TCP/IP Name Server Option The NetBIOS name server (NBNS) option specifies a list of RFC 1001/1002 [19] [20] NBNS name servers listed in order of preference. The code for this option is 44. The minimum length of the option is 4 octets, and the length must always be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+---- | 44 | n | a1 | a2 | a3 | a4 | b1 | b2 | b3 | b4 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+---- Alexander & Droms [Page 20] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 8.6. NetBIOS over TCP/IP Datagram Distribution Server Option The NetBIOS datagram distribution server (NBDD) option specifies a list of RFC 1001/1002 NBDD servers listed in order of preference. The code for this option is 45. The minimum length of the option is 4 octets, and the length must always be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+---- | 45 | n | a1 | a2 | a3 | a4 | b1 | b2 | b3 | b4 | ... +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+---- 8.7. NetBIOS over TCP/IP Node Type Option The NetBIOS node type option allows NetBIOS over TCP/IP clients which are configurable to be configured as described in RFC 1001/1002. The value is specified as a single octet which identifies the client type as follows: Value Node Type ----- --------- 0x1 B-node 0x2 P-node 0x4 M-node 0x8 H-node In the above chart, the notation '0x' indicates a number in base-16 (hexadecimal). The code for this option is 46. The length of this option is always 1. Code Len Node Type +-----+-----+-----------+ | 46 | 1 | see above | +-----+-----+-----------+ Alexander & Droms [Page 21] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 8.8. NetBIOS over TCP/IP Scope Option The NetBIOS scope option specifies the NetBIOS over TCP/IP scope parameter for the client as specified in RFC 1001/1002. See [19], [20], and [8] for character-set restrictions. The code for this option is 47. The minimum length of this option is 1. Code Len NetBIOS Scope +-----+-----+-----+-----+-----+-----+---- | 47 | n | s1 | s2 | s3 | s4 | ... +-----+-----+-----+-----+-----+-----+---- 8.9. X Window System Font Server Option This option specifies a list of X Window System [21] Font servers available to the client. Servers SHOULD be listed in order of preference. The code for this option is 48. The minimum length of this option is 4 octets, and the length MUST be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+--- | 48 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+--- 8.10. X Window System Display Manager Option This option specifies a list of IP addresses of systems that are running the X Window System Display Manager and are available to the client. Addresses SHOULD be listed in order of preference. The code for the this option is 49. The minimum length of this option is 4, and the length MUST be a multiple of 4. Code Len Address 1 Address 2 +-----+-----+-----+-----+-----+-----+-----+-----+--- | 49 | n | a1 | a2 | a3 | a4 | a1 | a2 | ... +-----+-----+-----+-----+-----+-----+-----+-----+--- Alexander & Droms [Page 22] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 9. DHCP Extensions This section details the options that are specific to DHCP. 9.1. Requested IP Address This option is used in a client request (DHCPDISCOVER) to allow the client to request that a particular IP address be assigned. The code for this option is 50, and its length is 4. Code Len Address +-----+-----+-----+-----+-----+-----+ | 50 | 4 | a1 | a2 | a3 | a4 | +-----+-----+-----+-----+-----+-----+ 9.2. IP Address Lease Time This option is used in a client request (DHCPDISCOVER or DHCPREQUEST) to allow the client to request a lease time for the IP address. In a server reply (DHCPOFFER), a DHCP server uses this option to specify the lease time it is willing to offer. The time is in units of seconds, and is specified as a 32-bit unsigned integer. The code for this option is 51, and its length is 4. Code Len Lease Time +-----+-----+-----+-----+-----+-----+ | 51 | 4 | t1 | t2 | t3 | t4 | +-----+-----+-----+-----+-----+-----+ 9.3. Option Overload This option is used to indicate that the DHCP "sname" or "file" fields are being overloaded by using them to carry DHCP options. A DHCP server inserts this option if the returned parameters will exceed the usual space allotted for options. If this option is present, the client interprets the specified additional fields after it concludes interpretation of the standard option fields. The code for this option is 52, and its length is 1. Legal values for this option are: Alexander & Droms [Page 23] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 Value Meaning ----- -------- 1 the "file" field is used to hold options 2 the "sname" field is used to hold options 3 both fields are used to hold options Code Len Value +-----+-----+-----+ | 52 | 1 |1/2/3| +-----+-----+-----+ 9.4. DHCP Message Type This option is used to convey the type of the DHCP message. The code for this option is 53, and its length is 1. Legal values for this option are: Value Message Type ----- ------------ 1 DHCPDISCOVER 2 DHCPOFFER 3 DHCPREQUEST 4 DHCPDECLINE 5 DHCPACK 6 DHCPNAK 7 DHCPRELEASE Code Len Type +-----+-----+-----+ | 53 | 1 | 1-7 | +-----+-----+-----+ 9.5. Server Identifier This option is used in DHCPOFFER and DHCPREQUEST messages, and may optionally be included in the DHCPACK and DHCPNAK messages. DHCP servers include this option in the DHCPOFFER in order to allow the client to distinguish between lease offers. DHCP clients indicate which of several lease offers is being accepted by including this option in a DHCPREQUEST message. The identifier is the IP address of the selected server. Alexander & Droms [Page 24] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 The code for this option is 54, and its length is 4. Code Len Address +-----+-----+-----+-----+-----+-----+ | 54 | 4 | a1 | a2 | a3 | a4 | +-----+-----+-----+-----+-----+-----+ 9.6. Parameter Request List This option is used by a DHCP client to request values for specified configuration parameters. The list of requested parameters is specified as n octets, where each octet is a valid DHCP option code as defined in this document. The client MAY list the options in order of preference. The DHCP server is not required to return the options in the requested order, but MUST try to insert the requested options in the order requested by the client. The code for this option is 55. Its minimum length is 1. Code Len Option Codes +-----+-----+-----+-----+--- | 55 | n | c1 | c2 | ... +-----+-----+-----+-----+--- 9.7. Message This option is used by a DHCP server to provide an error message to a DHCP client in a DHCPNAK message in the event of a failure. A client may use this option in a DHCPDECLINE message to indicate the why the client declined the offered parameters. The message consists of n octets of NVT ASCII text, which the client may display on an available output device. The code for this option is 56 and its minimum length is 1. Code Len Text +-----+-----+-----+-----+--- | 56 | n | c1 | c2 | ... +-----+-----+-----+-----+--- Alexander & Droms [Page 25] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 9.8. Maximum DHCP Message Size This option specifies the maximum length DHCP message that it is willing to accept. The length is specified as an unsigned 16-bit integer. A client may use the maximum DHCP message size option in DHCPDISCOVER or DHCPREQUEST messages, but should not use the option in DHCPDECLINE messages. The code for this option is 57, and its length is 2. The minimum legal value is 576 octets. Code Len Length +-----+-----+-----+-----+ | 57 | 2 | l1 | l2 | +-----+-----+-----+-----+ 9.9. Renewal (T1) Time Value This option specifies the time interval from address assignment until the client transitions to the RENEWING state. The value is in units of seconds, and is specified as a 32-bit unsigned integer. The code for this option is 58, and its length is 4. Code Len T1 Interval +-----+-----+-----+-----+-----+-----+ | 58 | 4 | t1 | t2 | t3 | t4 | +-----+-----+-----+-----+-----+-----+ 9.10. Rebinding (T2) Time Value This option specifies the time interval from address assignment until the client transitions to the REBINDING state. The value is in units of seconds, and is specified as a 32-bit unsigned integer. The code for this option is 59, and its length is 4. Code Len T2 Interval +-----+-----+-----+-----+-----+-----+ | 59 | 4 | t1 | t2 | t3 | t4 | +-----+-----+-----+-----+-----+-----+ Alexander & Droms [Page 26] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 9.11. Class-identifier This option is used by DHCP clients to optionally identify the type and configuration of a DHCP client. The information is a string of n octets, interpreted by servers. Vendors and sites may choose to define specific class identifiers to convey particular configuration or other identification information about a client. For example, the identifier may encode the client's hardware configuration. Servers not equipped to interpret the class-specific information sent by a client MUST ignore it (although it may be reported). The code for this option is 60, and its minimum length is 1. Code Len Class-Identifier +-----+-----+-----+-----+--- | 60 | n | i1 | i2 | ... +-----+-----+-----+-----+--- 9.12. Client-identifier This option is used by DHCP clients to specify their unique identifier. DHCP servers use this value to index their database of address bindings. This value is expected to be unique for all clients in an administrative domain. Identifiers consist of a type-value pair, similar to the It is expected that this field will typically contain a hardware type and hardware address, but this is not required. Current legal values for hardware types are defined in [22]. The code for this option is 61, and its minimum length is 2. Code Len Type Client-Identifier +-----+-----+-----+-----+-----+--- | 61 | n | t1 | i1 | i2 | ... +-----+-----+-----+-----+-----+--- 10. Extensions Additional generic data fields may be registered by contacting: Internet Assigned Numbers Authority (IANA) USC/Information Sciences Institute 4676 Admiralty Way Marina del Rey, California 90292-6695 or by email as: iana@isi.edu Alexander & Droms [Page 27] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 Implementation specific use of undefined generic types (those in the range 61-127) may conflict with other implementations, and registration is required. 11. Acknowledgements The authors would like to thank Philip Almquist for his feedback on this document. The comments of the DHCP Working Group are also gratefully acknowledged. In particular, Mike Carney and Jon Dreyer from SunSelect suggested the current format of the Vendor-specific Information option. RFC 1497 is based on earlier work by Philip Prindeville, with help from Drew Perkins, Bill Croft, and Steve Deering. 12. References [1] Droms, R., "Dynamic Host Configuration Protocol", RFC 1531, Bucknell University, October 1993. [2] Reynolds, J., "BOOTP Vendor Information Extensions", RFC 1497, USC/Information Sciences Institute, August 1993. [3] Croft, W., and J. Gilmore, "Bootstrap Protocol", RFC 951, Stanford University and Sun Microsystems, September 1985. [4] Braden, R., Editor, "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, USC/Information Sciences Institute, October 1989. [5] Mogul, J., and J. Postel, "Internet Standard Subnetting Procedure", STD 5, RFC 950, USC/Information Sciences Institute, August 1985. [6] Postel, J., and K. Harrenstien, "Time Protocol", STD 26, RFC 868, USC/Information Sciences Institute, SRI, May 1983. [7] Postel, J., "Name Server", IEN 116, USC/Information Sciences Institute, August 1979. [8] Mockapetris, P., "Domain Names - Implementation and Specification", STD 13, RFC 1035, USC/Information Sciences Institute, November 1987. [9] Postel, J., "Quote of the Day Protocol", STD 23, RFC 865, USC/Information Sciences Institute, May 1983. Alexander & Droms [Page 28] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 [10] McLaughlin, L., "Line Printer Daemon Protocol", RFC 1179, The Wollongong Group, August 1990. [11] Accetta, M., "Resource Location Protocol", RFC 887, CMU, December 1983. [12] Mogul, J. and S. Deering, "Path MTU Discovery", RFC 1191, DECWRL, Stanford University, November 1990. [13] Deering, S., "ICMP Router Discovery Messages", RFC 1256, Xerox PARC, September 1991. [14] Leffler, S. and M. Karels, "Trailer Encapsulations", RFC 893, U. C. Berkeley, April 1984. [15] Hornig, C., "Standard for the Transmission of IP Datagrams over Ethernet Networks", RFC 894, Symbolics, April 1984. [16] Postel, J. and J. Reynolds, "Standard for the Transmission of IP Datagrams Over IEEE 802 Networks", RFC 1042, USC/Information Sciences Institute, February 1988. [17] Sun Microsystems, "System and Network Administration", March 1990. [18] Mills, D., "Internet Time Synchronization: The Network Time Protocol", RFC 1305, UDEL, March 1992. [19] NetBIOS Working Group, "Protocol Standard for a NetBIOS Service on a TCP/UDP transport: Concepts and Methods", STD 19, RFC 1001, March 1987. [20] NetBIOS Working Group, "Protocol Standard for a NetBIOS Service on a TCP/UDP transport: Detailed Specifications", STD 19, RFC 1002, March 1987. [21] Scheifler, R., "FYI On the X Window System", FYI 6, RFC 1198, MIT Laboratory for Computer Science, January 1991. [22] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 1340, USC/Information Sciences Institute, July 1992. 13. Security Considerations Security issues are not discussed in this memo. Alexander & Droms [Page 29] RFC 1533 DHCP Options and BOOTP Vendor Extensions October 1993 14. Authors' Addresses Steve Alexander Lachman Technology, Inc. 1901 North Naper Boulevard Naperville, IL 60563-8895 Phone: (708) 505-9555 x256 EMail: stevea@lachman.com Ralph Droms Computer Science Department 323 Dana Engineering Bucknell University Lewisburg, PA 17837 Phone: (717) 524-1145 EMail: droms@bucknell.edu Alexander & Droms [Page 30] 8.7. RFC 1350 Network Working Group K. Sollins Request For Comments: 1350 MIT STD: 33 July 1992 Obsoletes: RFC 783 THE TFTP PROTOCOL (REVISION 2) Status of this Memo This RFC specifies an IAB standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited. Summary TFTP is a very simple protocol used to transfer files. It is from this that its name comes, Trivial File Transfer Protocol or TFTP. Each nonterminal packet is acknowledged separately. This document describes the protocol and its types of packets. The document also explains the reasons behind some of the design decisions. Acknowlegements The protocol was originally designed by Noel Chiappa, and was redesigned by him, Bob Baldwin and Dave Clark, with comments from Steve Szymanski. The current revision of the document includes modifications stemming from discussions with and suggestions from Larry Allen, Noel Chiappa, Dave Clark, Geoff Cooper, Mike Greenwald, Liza Martin, David Reed, Craig Milo Rogers (of USC-ISI), Kathy Yellick, and the author. The acknowledgement and retransmission scheme was inspired by TCP, and the error mechanism was suggested by PARC's EFTP abort message. The May, 1992 revision to fix the "Sorcerer's Apprentice" protocol bug [4] and other minor document problems was done by Noel Chiappa. This research was supported by the Advanced Research Projects Agency of the Department of Defense and was monitored by the Office of Naval Research under contract number N00014-75-C-0661. 1. Purpose TFTP is a simple protocol to transfer files, and therefore was named the Trivial File Transfer Protocol or TFTP. It has been implemented on top of the Internet User Datagram protocol (UDP or Datagram) [2] Sollins [Page 1] RFC 1350 TFTP Revision 2 July 1992 so it may be used to move files between machines on different networks implementing UDP. (This should not exclude the possibility of implementing TFTP on top of other datagram protocols.) It is designed to be small and easy to implement. Therefore, it lacks most of the features of a regular FTP. The only thing it can do is read and write files (or mail) from/to a remote server. It cannot list directories, and currently has no provisions for user authentication. In common with other Internet protocols, it passes 8 bit bytes of data. Three modes of transfer are currently supported: netascii (This is ascii as defined in "USA Standard Code for Information Interchange" [1] with the modifications specified in "Telnet Protocol Specification" [3].) Note that it is 8 bit ascii. The term "netascii" will be used throughout this document to mean this particular version of ascii.); octet (This replaces the "binary" mode of previous versions of this document.) raw 8 bit bytes; mail, netascii characters sent to a user rather than a file. (The mail mode is obsolete and should not be implemented or used.) Additional modes can be defined by pairs of cooperating hosts. Reference [4] (section 4.2) should be consulted for further valuable directives and suggestions on TFTP. 2. Overview of the Protocol Any transfer begins with a request to read or write a file, which also serves to request a connection. If the server grants the request, the connection is opened and the file is sent in fixed length blocks of 512 bytes. Each data packet contains one block of data, and must be acknowledged by an acknowledgment packet before the next packet can be sent. A data packet of less than 512 bytes signals termination of a transfer. If a packet gets lost in the network, the intended recipient will timeout and may retransmit his last packet (which may be data or an acknowledgment), thus causing the sender of the lost packet to retransmit that lost packet. The sender has to keep just one packet on hand for retransmission, since the lock step acknowledgment guarantees that all older packets have been received. Notice that both machines involved in a transfer are considered senders and receivers. One sends data and receives acknowledgments, the other sends acknowledgments and receives data. Most errors cause termination of the connection. An error is signalled by sending an error packet. This packet is not acknowledged, and not retransmitted (i.e., a TFTP server or user may terminate after sending an error message), so the other end of the connection may not get it. Therefore timeouts are used to detect such a termination when the error packet has been lost. Errors are Sollins [Page 2] RFC 1350 TFTP Revision 2 July 1992 caused by three types of events: not being able to satisfy the request (e.g., file not found, access violation, or no such user), receiving a packet which cannot be explained by a delay or duplication in the network (e.g., an incorrectly formed packet), and losing access to a necessary resource (e.g., disk full or access denied during a transfer). TFTP recognizes only one error condition that does not cause termination, the source port of a received packet being incorrect. In this case, an error packet is sent to the originating host. This protocol is very restrictive, in order to simplify implementation. For example, the fixed length blocks make allocation straight forward, and the lock step acknowledgement provides flow control and eliminates the need to reorder incoming data packets. 3. Relation to other Protocols As mentioned TFTP is designed to be implemented on top of the Datagram protocol (UDP). Since Datagram is implemented on the Internet protocol, packets will have an Internet header, a Datagram header, and a TFTP header. Additionally, the packets may have a header (LNI, ARPA header, etc.) to allow them through the local transport medium. As shown in Figure 3-1, the order of the contents of a packet will be: local medium header, if used, Internet header, Datagram header, TFTP header, followed by the remainder of the TFTP packet. (This may or may not be data depending on the type of packet as specified in the TFTP header.) TFTP does not specify any of the values in the Internet header. On the other hand, the source and destination port fields of the Datagram header (its format is given in the appendix) are used by TFTP and the length field reflects the size of the TFTP packet. The transfer identifiers (TID's) used by TFTP are passed to the Datagram layer to be used as ports; therefore they must be between 0 and 65,535. The initialization of TID's is discussed in the section on initial connection protocol. The TFTP header consists of a 2 byte opcode field which indicates the packet's type (e.g., DATA, ERROR, etc.) These opcodes and the formats of the various types of packets are discussed further in the section on TFTP packets. Sollins [Page 3] RFC 1350 TFTP Revision 2 July 1992 --------------------------------------------------- | Local Medium | Internet | Datagram | TFTP | --------------------------------------------------- Figure 3-1: Order of Headers 4. Initial Connection Protocol A transfer is established by sending a request (WRQ to write onto a foreign file system, or RRQ to read from it), and receiving a positive reply, an acknowledgment packet for write, or the first data packet for read. In general an acknowledgment packet will contain the block number of the data packet being acknowledged. Each data packet has associated with it a block number; block numbers are consecutive and begin with one. Since the positive response to a write request is an acknowledgment packet, in this special case the block number will be zero. (Normally, since an acknowledgment packet is acknowledging a data packet, the acknowledgment packet will contain the block number of the data packet being acknowledged.) If the reply is an error packet, then the request has been denied. In order to create a connection, each end of the connection chooses a TID for itself, to be used for the duration of that connection. The TID's chosen for a connection should be randomly chosen, so that the probability that the same number is chosen twice in immediate succession is very low. Every packet has associated with it the two TID's of the ends of the connection, the source TID and the destination TID. These TID's are handed to the supporting UDP (or other datagram protocol) as the source and destination ports. A requesting host chooses its source TID as described above, and sends its initial request to the known TID 69 decimal (105 octal) on the serving host. The response to the request, under normal operation, uses a TID chosen by the server as its source TID and the TID chosen for the previous message by the requestor as its destination TID. The two chosen TID's are then used for the remainder of the transfer. As an example, the following shows the steps used to establish a connection to write a file. Note that WRQ, ACK, and DATA are the names of the write request, acknowledgment, and data types of packets respectively. The appendix contains a similar example for reading a file. Sollins [Page 4] RFC 1350 TFTP Revision 2 July 1992 1. Host A sends a "WRQ" to host B with source= A's TID, destination= 69. 2. Host B sends a "ACK" (with block number= 0) to host A with source= B's TID, destination= A's TID. At this point the connection has been established and the first data packet can be sent by Host A with a sequence number of 1. In the next step, and in all succeeding steps, the hosts should make sure that the source TID matches the value that was agreed on in steps 1 and 2. If a source TID does not match, the packet should be discarded as erroneously sent from somewhere else. An error packet should be sent to the source of the incorrect packet, while not disturbing the transfer. This can be done only if the TFTP in fact receives a packet with an incorrect TID. If the supporting protocols do not allow it, this particular error condition will not arise. The following example demonstrates a correct operation of the protocol in which the above situation can occur. Host A sends a request to host B. Somewhere in the network, the request packet is duplicated, and as a result two acknowledgments are returned to host A, with different TID's chosen on host B in response to the two requests. When the first response arrives, host A continues the connection. When the second response to the request arrives, it should be rejected, but there is no reason to terminate the first connection. Therefore, if different TID's are chosen for the two connections on host B and host A checks the source TID's of the messages it receives, the first connection can be maintained while the second is rejected by returning an error packet. 5. TFTP Packets TFTP supports five types of packets, all of which have been mentioned above: opcode operation 1 Read request (RRQ) 2 Write request (WRQ) 3 Data (DATA) 4 Acknowledgment (ACK) 5 Error (ERROR) The TFTP header of a packet contains the opcode associated with that packet. Sollins [Page 5] RFC 1350 TFTP Revision 2 July 1992 2 bytes string 1 byte string 1 byte ------------------------------------------------ | Opcode | Filename | 0 | Mode | 0 | ------------------------------------------------ Figure 5-1: RRQ/WRQ packet RRQ and WRQ packets (opcodes 1 and 2 respectively) have the format shown in Figure 5-1. The file name is a sequence of bytes in netascii terminated by a zero byte. The mode field contains the string "netascii", "octet", or "mail" (or any combination of upper and lower case, such as "NETASCII", NetAscii", etc.) in netascii indicating the three modes defined in the protocol. A host which receives netascii mode data must translate the data to its own format. Octet mode is used to transfer a file that is in the 8-bit format of the machine from which the file is being transferred. It is assumed that each type of machine has a single 8-bit format that is more common, and that that format is chosen. For example, on a DEC-20, a 36 bit machine, this is four 8-bit bytes to a word with four bits of breakage. If a host receives a octet file and then returns it, the returned file must be identical to the original. Mail mode uses the name of a mail recipient in place of a file and must begin with a WRQ. Otherwise it is identical to netascii mode. The mail recipient string should be of the form "username" or "username@hostname". If the second form is used, it allows the option of mail forwarding by a relay computer. The discussion above assumes that both the sender and recipient are operating in the same mode, but there is no reason that this has to be the case. For example, one might build a storage server. There is no reason that such a machine needs to translate netascii into its own form of text. Rather, the sender might send files in netascii, but the storage server might simply store them without translation in 8-bit format. Another such situation is a problem that currently exists on DEC-20 systems. Neither netascii nor octet accesses all the bits in a word. One might create a special mode for such a machine which read all the bits in a word, but in which the receiver stored the information in 8-bit format. When such a file is retrieved from the storage site, it must be restored to its original form to be useful, so the reverse mode must also be implemented. The user site will have to remember some information to achieve this. In both of these examples, the request packets would specify octet mode to the foreign host, but the local host would be in some other mode. No such machine or application specific modes have been specified in TFTP, but one would be compatible with this specification. It is also possible to define other modes for cooperating pairs of Sollins [Page 6] RFC 1350 TFTP Revision 2 July 1992 hosts, although this must be done with care. There is no requirement that any other hosts implement these. There is no central authority that will define these modes or assign them names. 2 bytes 2 bytes n bytes ---------------------------------- | Opcode | Block # | Data | ---------------------------------- Figure 5-2: DATA packet Data is actually transferred in DATA packets depicted in Figure 5-2. DATA packets (opcode = 3) have a block number and data field. The block numbers on data packets begin with one and increase by one for each new block of data. This restriction allows the program to use a single number to discriminate between new packets and duplicates. The data field is from zero to 512 bytes long. If it is 512 bytes long, the block is not the last block of data; if it is from zero to 511 bytes long, it signals the end of the transfer. (See the section on Normal Termination for details.) All packets other than duplicate ACK's and those used for termination are acknowledged unless a timeout occurs [4]. Sending a DATA packet is an acknowledgment for the first ACK packet of the previous DATA packet. The WRQ and DATA packets are acknowledged by ACK or ERROR packets, while RRQ 2 bytes 2 bytes --------------------- | Opcode | Block # | --------------------- Figure 5-3: ACK packet and ACK packets are acknowledged by DATA or ERROR packets. Figure 5-3 depicts an ACK packet; the opcode is 4. The block number in an ACK echoes the block number of the DATA packet being acknowledged. A WRQ is acknowledged with an ACK packet having a block number of zero. Sollins [Page 7] RFC 1350 TFTP Revision 2 July 1992 2 bytes 2 bytes string 1 byte ----------------------------------------- | Opcode | ErrorCode | ErrMsg | 0 | ----------------------------------------- Figure 5-4: ERROR packet An ERROR packet (opcode 5) takes the form depicted in Figure 5-4. An ERROR packet can be the acknowledgment of any other type of packet. The error code is an integer indicating the nature of the error. A table of values and meanings is given in the appendix. (Note that several error codes have been added to this version of this document.) The error message is intended for human consumption, and should be in netascii. Like all other strings, it is terminated with a zero byte. 6. Normal Termination The end of a transfer is marked by a DATA packet that contains between 0 and 511 bytes of data (i.e., Datagram length < 516). This packet is acknowledged by an ACK packet like all other DATA packets. The host acknowledging the final DATA packet may terminate its side of the connection on sending the final ACK. On the other hand, dallying is encouraged. This means that the host sending the final ACK will wait for a while before terminating in order to retransmit the final ACK if it has been lost. The acknowledger will know that the ACK has been lost if it receives the final DATA packet again. The host sending the last DATA must retransmit it until the packet is acknowledged or the sending host times out. If the response is an ACK, the transmission was completed successfully. If the sender of the data times out and is not prepared to retransmit any more, the transfer may still have been completed successfully, after which the acknowledger or network may have experienced a problem. It is also possible in this case that the transfer was unsuccessful. In any case, the connection has been closed. 7. Premature Termination If a request can not be granted, or some error occurs during the transfer, then an ERROR packet (opcode 5) is sent. This is only a courtesy since it will not be retransmitted or acknowledged, so it may never be received. Timeouts must also be used to detect errors. Sollins [Page 8] RFC 1350 TFTP Revision 2 July 1992 I. Appendix Order of Headers 2 bytes ---------------------------------------------------------- | Local Medium | Internet | Datagram | TFTP Opcode | ---------------------------------------------------------- TFTP Formats Type Op # Format without header 2 bytes string 1 byte string 1 byte ----------------------------------------------- RRQ/ | 01/02 | Filename | 0 | Mode | 0 | WRQ ----------------------------------------------- 2 bytes 2 bytes n bytes --------------------------------- DATA | 03 | Block # | Data | --------------------------------- 2 bytes 2 bytes ------------------- ACK | 04 | Block # | -------------------- 2 bytes 2 bytes string 1 byte ---------------------------------------- ERROR | 05 | ErrorCode | ErrMsg | 0 | ---------------------------------------- Initial Connection Protocol for reading a file 1. Host A sends a "RRQ" to host B with source= A's TID, destination= 69. 2. Host B sends a "DATA" (with block number= 1) to host A with source= B's TID, destination= A's TID. Sollins [Page 9] RFC 1350 TFTP Revision 2 July 1992 Error Codes Value Meaning 0 Not defined, see error message (if any). 1 File not found. 2 Access violation. 3 Disk full or allocation exceeded. 4 Illegal TFTP operation. 5 Unknown transfer ID. 6 File already exists. 7 No such user. Internet User Datagram Header [2] (This has been included only for convenience. TFTP need not be implemented on top of the Internet User Datagram Protocol.) Format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Destination Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Values of Fields Source Port Picked by originator of packet. Dest. Port Picked by destination machine (69 for RRQ or WRQ). Length Number of bytes in UDP packet, including UDP header. Checksum Reference 2 describes rules for computing checksum. (The implementor of this should be sure that the correct algorithm is used here.) Field contains zero if unused. Note: TFTP passes transfer identifiers (TID's) to the Internet User Datagram protocol to be used as the source and destination ports. Sollins [Page 10] RFC 1350 TFTP Revision 2 July 1992 References [1] USA Standard Code for Information Interchange, USASI X3.4-1968. [2] Postel, J., "User Datagram Protocol," RFC 768, USC/Information Sciences Institute, 28 August 1980. [3] Postel, J., "Telnet Protocol Specification," RFC 764, USC/Information Sciences Institute, June, 1980. [4] Braden, R., Editor, "Requirements for Internet Hosts -- Application and Support", RFC 1123, USC/Information Sciences Institute, October 1989. Security Considerations Since TFTP includes no login or access control mechanisms, care must be taken in the rights granted to a TFTP server process so as not to violate the security of the server hosts file system. TFTP is often installed with controls such that only files that have public read access are available via TFTP and writing files via TFTP is disallowed. Author's Address Karen R. Sollins Massachusetts Institute of Technology Laboratory for Computer Science 545 Technology Square Cambridge, MA 02139-1986 Phone: (617) 253-6006 EMail: SOLLINS@LCS.MIT.EDU Sollins [Page 11] 8.8. Install Instructions I N S T A L L A T I O N Overview of the installation process ==================================== Due to it's nature this package requires at least two computer systems. One acts as a server, and at least one other will be setup as a diskless client. Therefore this installation guide is divided into four sections: 1.) Compilation and installation of utility programs on the server 2.) Create a netbootable image of the target operating system 3.) Setup of the server 4.) Setup of the client including building the bootrom The server has to support TCP/IP and certain protocols based on this network standard. Most likely this will be a Unix-type server. Though it's probably possible to also use servers running OS/2 or Windows-NT, for example, all server related programs in this package can currently only be compiled on a Unix-type host. This requirement is independed of the operating system which is later booted on the diskless client. Therefore even if you want to boot MS-DOS on your client(s) you need at least one Unix-type computer for program compilation and generation of all boot files. Lateron when all necessary files are built you can use any server you want. This package contains two main parts: 1.) The bootrom source and binaries. This part gets installed on the diskless client. All binaries except for utility programs are already precompiled. There are no further user changeable or adjustable options in the sources so you don't have to have access to the 16 bit development tools in order to use the boot- rom. You can just use the binaries provided. In order for the bootrom to access the network card in your diskless client you need a driver. Currently the bootrom only supports so called packet drivers, which are normally used on MS-DOS systems to interface a network stack with the hardware. With this package only the packet driver binaries are required, so you don't need to recompile anything here as well. You can find precompiled packet drivers for many popular network cards on any SimTel FTP mirror (it's called Crynwr packet driver col- lection), and for those of you without internet access some of those packet driver binaries are included with this package. Another good source for a packet driver for your network card might be it's manufacturer. At least the well known manufacturers (3Com and SMC for example) provide packet drivers for their complete product line. Those manufacturer provided packet drivers are usually faster and easier to install than those from the Crynwr collection, and can sometimes determine the hardware configuration at runtime, which the Crynwr drivers can't. However, there is a limitation in that you can only use packet drivers which are COM-type executables. EXE-type programs are not supported yet. 2.) A set of programs to generate netbootable images on the server. These programs are called mknbi-, where identifies the operating system which is lateron running on the diskless client. Currently only Linux and MS-DOS are supported. There is another requirement which should not leave unnoted. Although you can build a bootrom with slightly limited functionality which is less than 16kB in size, the usual size for a bootrom will be between 16kB and 32kB. Therefore when you go shopping for a network card you should try to get one which is able to support 32kB EPROM's. This is standard on almost all cards from major manufacturers, but most cheap NE2000 are known to allow only a maximum of 16kB. Also note that some network cards from 3Com and SMC allow you to select ROM sizes of 32kB and more with their configuration programs, but can physically support only 16kB! Compilation and installation of utility programs on the server ============================================================== This package uses GNU's autoconf to configure the compilation process of the utility programs. You shouldn't have any problems to compile these programs on any Unix-type system. 1.) Cd into the netboot directory and run ./configure. It's a configuration script generated by autoconf and checks for header files and system specific details. The mknbi utility programs contain some Intel assembler modules which lateron run on the diskless client. If you want to assemble these modules you need as86 and ld86, which you can get for free for Unix systems. However, there are preassembled files available so you actually don't need these two programs. configure checks for their existence and creates the Makefiles accordingly. For an explanation of the switches available to configure just run it with the --help option. Some additional switches are available: --disable-mknbi-linux --disable-mknbi-dos Choose these options if you don't want to create any of the corresponding mknbi utility programs. There is also another configure option: --enable-bootrom Use this option only if you want to recompile the bootrom itself. If you want to use the precompiled binaries, you don't need to specify this switch. See the file INSTALL.bootrom about how to recompile the bootrom. 2.) Check that all generated Makefiles and the config.h are correct for your system. 3.) Compile all programs with make clean make This will compile all programs without those which you disabled during the configuration stage. IMPORTANT NOTE: Some Makefiles use ifdef, which not every make program understands. If you get an error from make (usually in the form: "missing delimiter") then get and install GNU make on your system! Especially System V systems are known to have this deficiency. 4.) If you want to permanently install the utility programs on your server you can run make install This will also install the corresponding man pages for later reference. However, it's perfectly ok to skip this step and run the mknbi program from their source directories. But please note that they are just called "mknbi" within their source directories. Therefore if you read further down to run mknbi-dos, you have to use "./mknbi-dos/mknbi" instead if you didn't install the programs using 'make install'. Create a netbootable image of the target operating system ========================================================= This step of the installation process depends on which operating you want to boot on your diskless clients. Everything described in this chapter does not depend on working on a Linux system. You can use any UNIX type system to create the netbootable images. Linux: With Linux you have far too many options to list them all in this text. Please refer to the mknbi-linux man page for all details. I will only describe the most common ways to setup a diskless Linux client here. First you have to decide where the Linux client is going to mount it's root filesystem from. This can either be a directory on an NFS server or a ram disk. Setup your Linux kernel accordingly. To use a root filesystem on an NFS server you should include TCP/IP network support into the kernel together with support for NFS file- systems. You cannot load this NFS support using a module as it has to be available at bootup. Additionally you also have to select NFSROOT support during kernel configuration. However, you don't need BOOTP or RARP support. Accordingly if you want to use ramdisk support the filesystem type you are going to use on the ramdisk has to be permanently compiled into the kernel. Also initrd has to be included in that case. 1.) Configuring for NFS root filesystem. Next copy your Linux kernel into the current directory and run mknbi-linux: mknbi-linux -d rom -i rom -k zImage -o bootImage This supposes that your kernel image is called zImage, and gives you a netbootable image named bootImage. 2.) Configuring for root filesystem on ramdisk If you want to use a ramdisk as a root device you have to create a ramdisk image first. Probably the easiest way to setup such an image is to use a floppy, though you can also use the loopback device if you are working on a Linux host. First format the floppy and make a filesystem on it. Next copy all programs and files onto it which you want to have on the root filesystem of the diskless client lateron. You should then test your root floppy. To do this copy your kernel onto another floppy with dd and set it's root device to floppy using rdev: dd if=zImage of=/dev/fd0 rdev /dev/fd0 /dev/fd0 Now boot your diskless client using this boot disk. After the kernel started up, it will ask you to insert the root floppy and to press enter. Your root floppy will be mounted. If everything works as you intended, you can now create a netbootable image. Re-insert the root floppy into your server system (or whereever this netboot directory is located), and type: dd if=/dev/fd0 of=ramImage gzip -9 ramImage mknbi-linux -d ram -i rom -r ramImage.gz -k zImage -o bootImage Like above this will now give you a file bootImage with the netbootable Linux kernel image in it. MS-DOS: To boot DOS on your diskless client you have to have MS-DOS Version 5.0 or higher. Windows-95 has an internal DOS called version 7.0, so it should be no problem to use it as well. Older MS-DOS versions will definitely not work. I haven't had a chance to test any other DOS like Novell-DOS or DR-DOS. Give them a try, and tell me. First you have to create a directory which contains all the files the client will see on it's boot drive (either A: or C:). This can either be the root directory on a DOS floppy or any directory on the system on which you installed mknbi-dos. In the first case it has to be a floppy which contains a bootable DOS system, i.e. which has been created with format a: /s on a DOS system. If the directory resides on a UNIX system, you have to copy the two system files msdos.sys and io.sys, which are part of MS-DOS, into it by yourself. To do this I recommend using mread of the MTools, which are freely available for almost every UNIX system. After you created the directory or floppy which lateron becomes the clients boot drive, you should copy all other necessary files into it. This will probably include programs to setup a network environment on the client. When editing text files for the client please note that they usually have to be in MS-DOS format with lines ending in Carriage-Return/Linefeed instead of just Linefeed as it is common on UNIX systems. When you are finished setting up the clients boot directory, first get a copy of the floppy disk image, and then run mknbi-dos to create a netbootable image: dd if=/dev/fd0 of=fdImage mknbi-dos -r fdImage -o bootImage This assumes that you inserted the boot floppy into the fd0 drive of your UNIX system, and will create a file named bootImage. If you used a UNIX directory, substitute fdImage with it's name. mknbi-dos will automatically detect wether it is a directory, an ordinary file or a block device. By default mknbi-dos creates a netbootable image, which lateron mounts the ram disk as the A: drive on your client. If you want to mount the ram disk as C: instead, you should include the '-c' switch to the call of mknbi-dos. The difference between mounting the ram disk as a floppy (A:) or hard disk (C:) is, that with the floppy option the ram disk can be removed lateron, maybe after a network redirector has been loaded, which makes the ram disk obsolete. This is not possible with a virtual hard disk drive. On the other hand side, when using the ram disk as C: you can specify a different ramdisk size with the '-s' option. Please refer to the man page for mknbi-dos for further information. Setup of the server =================== Setup of the server depends on the kind of server you are using. There- fore all further explanations in this chapter can only serve as a general guide. You should consult your server's documentation as the final autho- rity. When the bootrom starts on the client it first tries to query a bootp server for information like IP numbers and the name of the boot image file. Such a bootp server program is usually called bootpd. Most sun servers use a program called bootparamd instead. Note that you _cannot_ use bootparamd as a substitute for bootpd as both programs use different protocols. Install a publicly available bootpd instead on your sun. Next you should copy the bootImage file, which you have created in the previous step above, into a publicly accessible directory (called /boot for example). If you want to boot more than one diskless client you can use the same bootImage file for every client. However, if you configured for a ramdisk (with Linux or DOS) and the ramdisk image contains different files or information for every client, you will obviously also need a different bootImage file for each client. Then you need to setup a boot description file for bootpd, which is usually called /etc/bootptab. Consult your server's documentation for further information. However, the entries in this file will usually look something like this for every diskless client: client1:hd=/boot:vm=auto:ip=192.109.225.66:\ :ht=ethernet:ha=004001417173:\ :bf=bootImage-client1:rp=/boot/client1/root which you created in the previous step. Therefore the full pathname for the bootImage file for the diskless system called "client1" will be /boot/bootImage-client1 with this sample entry. The 'ip' tag specifies the IP address of the client, ware address. The 'vm=auto' tag tells bootpd to use the same vendor encoding as the bootrom. If your diskless client is going to use it's root filesystem via NFS you should also specify the directory on the server which gets mounted lateron with the 'rp' tag. However, if your diskless client uses a ramdisk, you can omit 'rp'. When you choose to use the standard bootrom with ANSI display driver (see below for further information) you could also setup a menu for letting the user select different boot image files. See the additional file INSTALL.menu about how to use this feature. But I recommend to first use the standard way of setting up the bootptab file as described above. You can always add a user menu lateron. Of course you should also remember to get bootpd running on the server, either on bootup from /etc/rc or some similar mechanism, or from inetd. Again, see your server's documentation about how to do this. The next step preformed by the bootrom after querying the bootp server is to load in the boot image file specified by the 'hd' and 'bf' tags in /etc/bootptab. To do this a protocol named tftp is used. Therefore you will next have to setup a daemon process for this protocol on your server. Such a daemon is usually called tftpd, and you should again remember to get tftpd running, usually via inetd. Since the TFTP protocol is very insecure access to the tftpd server is usually restricted, either within tftpd itself, or with a TCP/IP wrapper like tcpd. tcpd for example uses host access control tables which are stored in /etc/hosts.allow and /etc/hosts.deny. See tftpd(8), tcpd(8) and hosts_access(5) as well as your server's documentation for further information. If you selected a ramdisk for the diskless client's root directory you are now finished with the server setup. But if your client is going to use NFS (either directly like with booting Linux, or by using programs included on the ram disk) you should now setup everything which is necessary for moun- ting an NFS directory on the server. This usually involves running several programs: portmap, mountd, nfsd and optionally ugidd. portmap usually doesn't require editing any configuration files. But for mountd and nfsd you need to specify the permissions which allow the client to access the required directories on the server. These permissions are usually set with a file called /etc/exports. Typically it looks like this for our sample client: # # Export directories for client1 (diskless workstation) # /boot/client1/root client1(rw,link_absolute) /boot/client1/usr client1(rw,link_absolute) If you use 'map-daemon' to map UID and GID numbers on the server you should remember to also configure and run ugidd on the server. Please consult your server's documentation for further information regarding setup of NFS exports. You might also want to check out the portmap(8), nfsd(8), mountd(8) and ugidd(8) man pages. Also remember that access to any of these services might be restricted with tcpd on your server. Another important step is to fill up the root directory for the disk- less client. It has to contain all files necessary for the client to startup and mount further directories via NFS (like a /usr filesystem as specified in the /etc/exports example above). How to setup this root directory is far beyond the scope of this documentation. Just one hint: if your server is _not_ running Linux, you should be aware of major/minor number assignments in the /boot/client1/root/dev directory. For example, simply using mknod on an AIX server will eventually give you wrong major/minor number when the directory is later exported to a Linux diskless client. With some configurations AIX will add a certain offset to all major numbers which makes them unusable for Linux. Refer to your server's manuals for further information. You might also find some useful hints in the file Documentation/nfsroot.txt in the Linux source tree, if your diskless client is booting Linux. Setup of the client including building the bootrom ================================================== Until now you only had to work on the server (with the exception of maybe booting your diskless client from a diskette to check the correctness of the root filesystem). As the last step we can now go on and setup the diskless client itself. The first step is to configure the network card in the diskless client. For this refer to the manual which came with the network card. Some cards require setting of jumpers. Others have setup programs which have to be run. After configuring the network interface write down all necessary hardware parameters like I/O addresses, memory addresses, interrupt line number or DMA channel numbers, as you might need this information lateron in the configuration process. Next change into the netboot directory on your UNIX system (where this documentation file is in) and type make bootrom This will compile all necessary utility programs and then run the configuration program. It will first ask you which bootrom kernel you want to use. The minimal kernel is necessary for network cards which only allow up to 16 kB ROM size, and kernel86 can be used to boot on 16-bit systems (older than 386), for example for booting MS-DOS. Unless you have any special requirements you should choose the standard kernel. Then you have to specify the packet driver to use for your network card. You can either choose one of the supplied drivers, or provide your own. If you want to provide your own driver you have to give the full path name of the packet driver binary on your server, and also specify all necessary options to run it. Don't specify any options here which switch the packet driver into windows mode or which allow it to work for disk- less systems. Those options are for Novell network bootroms only, and are not necessary for this bootrom. If you use one of the drivers in the list shown, the configuration program will ask you about all necessary hardware information to run the packet driver which you selected. This usually includes the I/O address of the network card, it's interrupt number and a DMA channel number. Note that only that information is requested which is really necessary. You should have your network card information handy when entering this information. Some packet drivers are able to determine hardware related information at runtime and therefore don't require any further information. If you did not select the minimal kernel, the configuration program is next going to ask you wether you want to include some additional drivers. First it lets you select the ANSI display driver. This will allow you to draw nice menus on the screen with the standard bootrom kernel. You can then select the packet driver debugging program. It's an additional module to trace network problems and is usually not re- quired. It shows you the first couple bytes of all packets (where the UDP/IP headers are encoded) going through the packet driver during boot time of the diskless client. Only select this debugging module if you run into problems during the initial network boot process of the bootrom _and_ you know how to decode the UDP/IP header infor- mation. The configuration program will also ask you about any additional modules you want to install into the bootrom. These modules have to be standard DOS COM-type programs, and can, for example, preset the network card to a special state before the packet driver starts, or setup a serial line to support booting over a PPP or SLIP connec- tion (the Crynwr packet driver collection also contains a SLIP packet driver which is not provided in this package). However note that the total size of the resulting bootrom image can't be larger than 64kB. After you answered all questions the configuration program is creating the bootrom according to your specifications. It first combines the bootrom kernel with all selected modules, then compresses the resulting file and adds the bootrom startup code. When the configuration program has finished you will find two new files in the current directory: image.flo - this file can be written onto a floppy using dd image.rom - image to be burned into an EPROM You should now copy image.flo onto a floppy using dd if=image.flo of=/dev/fd0 and then boot your diskless client using this floppy. If you have setup everything (including your network card) you will see the bootrom code starting, querying the bootp server and loading the boot image file. When everything works as required you can then go on and burn the file image.rom into an EPROM. Please consult the manual of your EPROM burner how to do this. It usually requires converting the image file into a special format (Intel or Motorola hex format for example). Insert the EPROM into the socket on your network card and turn on the diskless system. You should now see the bootrom coming up. Another way of getting the bootrom code into your client is using the Flash-EPROM card (called FlashCard), for which you can find a schematic and PCB layout in this package. You can use image.rom directly to burn it into FlashCard - there is no hex conversion necessary. About how to use and program the FlashCard see the documentation in the FlashCard directory. In case you want to create new bootroms without always having the sources around, you can now install the binaries created during the configuration step with the command make bootrom_install This will copy all necessary binaries for creating new bootroms into the directory $prefix/lib/netboot where $prefix is either /usr/local or the prefix you specified with running GNU configure. The typical path would be /usr/local/lib/netboot. It will also install the makerom script into $prefix/bin, so you just have to type makerom to create a new bootrom. Appendix: Recompiling the bootrom ======== If you want to recompile the bootrom for some reason, checkout the file INSTALL.bootrom for further information. However, you don't need to re- compile the bootrom in order to just use it! 8.9. Troubleshoot Problems T R O U B L E S H O O T I N G If you run into any problem during installation or when using this package, please first read the following text and all other relevant documentation. Especially you should consult your server's documen- tation if you run into problems setting up your server. Also refer to your network card's user manual or the documentation for the operating systems of the diskless clients accordingly. However, if you still can't solve the problem on your own, you can send me an email to gero@gkminix.han.de Users able to speak German can send me the mail in german. Otherwise please write in english. I already received some emails in so poor english that I haven't been able to even understand the problem. I can't help you in that case. And please excuse me that I can't answer questions sent to me by standard mail or telephone calls. I just don't have the time for dealing with that. If you decided to send me an email please describe your problem as exactly as possible. It usually helps to send me relevant portions of configuration files (I have to pay for my internet access by myself so please keep quotings as short as possible). Especially with problems with the bootrom it usually helps to _exactly_ write down the screen output, not only but including any error messages. Also state as exact as possible how you created the problem so that I can try to simulate it on my own hardware. Additionally please note that I can't help you with every problem with your server, as there are so many different systems on the market. The same is true for problems with network cards. I just don't have the financial capabilities to buy any card on the market for testing. Per- sonally I'm using NE2000 and WD8013 cards, so I can probably help you with those. If you find a problem which looks like a bug in the code I really appreciate a short notice from you. And if you have a fix for the bug I would even more appreciate your message. Besides contacting me directly there also exists a mailing list related to network booting which you can subscribe to. Write a mail with the message 'subscribe netboot' in it's body to majordomo@baghira.han.de (the subject of the mail doesn't matter). The readers of the mailing list should also be able to help you with any problem you might have while setting up a diskless client. And besides that I'm also going to announce any new version of this netboot package to the mailing list. Problem: My operating system OS/XY is not supported by netboot I would gladly provide support for every operating system on the market, but I don't have the resources for doing this. However, if you want a particular operating system to be supported, you should get in contact with me. In any case you will have to provide me with a valid and licensed copy of that operating system. You are also invited to write your own boot loader, and send it to me for inclusion into netboot under the terms of the GNU GPL. Problem: While trying to build a bootrom I get a compiler error The installation scripts require to compile a couple of utility programs which are only required during building the bootrom. They should compile on any Unix-type system, so if you get an error please report it to me, even when you are able to fix it yourself, so that I can include a patch for future releases. Problem: I get a an error from make saying something like "missing delimiter" Some of the Makefiles use ifdef's, which older make programs don't understand. Even some more "modern" systems like SCO Open-Server 5 have this problem. In that case you will have to get and install GNU make on your system (which is the better choice anyway). Problem: The bootrom doesn't startup at all Either you have a floppy in your diskette drive or you have a hard disk installed with a partition marked as active, and the bootrom has been built so that it lets the BIOS look for active partitions first. Both conditions let the system boot from the bootable media instead of using the bootrom. Just remove the floppy or use fdisk to mark all partitions as unbootable (e.g. inactive). Alternatively you can also build the bootrom so that it does not allow the BIOS to look for bootable partitions. The program which actually creates the bootrom ('makerom', it gets called when you run 'make bootrom') will ask you about this right after selecting the bootrom kernel image. Problem: The bootrom behaves strange during startup, and may even hangup the whole system If you compiled the mknbi programs on a system with big endian byte order (like Motorola or PPC systems) this might indicate that the configuration program couldn't find the correct byte order. It might also be that there is a bug in the byte ordering code. Some systems like SPARCs also do not allow data accesses at misaligned addresses. 'configure' should usually find out about these conditions. In any case, if 'configure' is not able to pro- perly detect what kind of system you are using, edit the file config.h by hand and try it again. Please report this condition, and also note which system you used for installation. Problem: The packet driver is not able to start properly First check what error message the packet driver prints. Usually this problem is a result of an incorrect setup of the network card, so check that it uses an I/O address, interrupt line and DMA channel (if applicable) of it's own, and that the packet driver uses the correct values. Another common problem with ethernet cards which use shared memory (like WD80?3 cards) is an overlap- ping of this shared memory with the rom area used by the bootrom. Select a different shared memory address in that case. If that's ok you should next check that you configured the packet driver correctly with the bootrom configuration program. Usually the packet driver prints out what it expects the hardware to look like so you can use this information to check up your setup. Problem: The bootrom tells me that there is not enough memory but I have xx megabytes installed This problem is a result of the fact that the BIOS starts the bootrom in the processor's real mode. The bootrom is therefore only able to access the lower 1 megabyte of memory, regardless of how much you installed. And 384kB of this is reserved for ROM's and the video memory, so there is only 640kB left. Unfor- tunately some systems even reserve memory from these lower 640kB for internal BIOS data. This is called extended BIOS data area, and known to be used on most PS/2 systems. But also some other BIOSes use such an extended BIOS data area, which is usually selectable in the system's setup. Therefore you should try to deselect such a feature. If that's not possible you are out of luck - sorry. Problem: The bootrom doesn't receive a bootp answer and just hangs printing dots First you should check if bootpd runs on your server or is started properly from inetd. Then check that the server's /etc/bootptab is setup correctly. Especially the hardware address and the client's IP address and name have to be correct. Most bootp servers have the ability to write debugging information into a log file. Use that feature to verify that your server really receives bootp requests from the client's bootrom and sends out a valid answer. Also check for error messages in the log file. Even if your bootpd doesn't write into a seperate log file it might use syslog on your system, so find the log file name from your syslogd configuration file and check for errors. If you are able to use a network tracing program like tcpdump you can check if the bootrom sends out correct requests and that the server is answering correctly. In that case it is more likely to be a problem in the bootrom, so you should create a new bootrom image with the packet driver debugging module included. You should then see the bootrom's request packets going out, and the server's answers coming in. If there are no packets coming in although you verified that the server is sending out correct replies there might be a problem with your network card. Did you set it up correctly, is a cable connected (no kidding, those things really happen)? If everything fails try to boot the diskless client with the intended operating system and try to access the network card using that operating system's tools. If the server is not sending out answer packets, but the bootpd logfiles indicates correct answers, it might be a problem with the arp setup on your server. Normally arp shouldn't be a concern for you. However, some older versions of bootpd for Linux had problems here, which could be solved by setting the kernel arp table manually. Problem: The bootrom did get a bootp answer but is not able to load the bootimage file This is likely to be a problem with the tftpd setup on the server. Does tftpd run when you startup the bootrom code? If not check that inetd is configured correctly. Also there might be a TCP/IP wrapper running on your server which might prohibit access to the tftp service (which is known to be very insecure and therefore a candidate for getting started by an internet security wrapper like tcpd). Check any access configuration files for tcpd. Furthermore tftpd has to be able to access the bootimage file. It usually runs as a user with very low priviliges because of security reasons and might not be allowed to read the bootimage file, so you should check and set the bootimage file's permissions correctly. Problem: The boot image loader reports an error Congratulations! You just discovered a bug in the boot loader. Please report it to me. Problem: When I'm using the bootrom menu to load a Unix system off the local hard disk, it reports some weird error messages to me (especially, SCO Unix says that it's not able to open boot device). However, booting without the bootrom works without a problem. Some operating systems, especially Unix like systems, read the partition table after booting and try to find their own boot par- tition. When using the bootrom, it's not necessary to mark the Unix partition as bootable, so the Unix startup loader fails. To solve this problem, mark the Unix partition active with some fdisk program. To avoid that it starts running instead of the bootrom, create the bootrom so that it does not allow the BIOS to search for boot partitions on the installed hard disks (the 'makerom' program, which gets run when you do a 'make bootrom', will ask you about this right after selecting a kernel image). Problem: I'm loading Linux onto my diskless client and the kernel tells me to insert a root floppy and press enter First you should check that you built your kernel correctly. It should have support for the root filesystem built in. If you want to use an NFS mounted directory as root the kernel should have TCP/IP support installed. Also it has to have a driver for your network card built in, and NFS and NFSROOT have to be both speci- fied. When using a ramdisk it's support has to be compiled in as well as support for the filesystem with which you formatted the ramdisk image. Please note that the loaded kernel is not able to use modules at bootup time (only _after_ the root file- system has been mounted, but not before), so everything has to be compiled in. If the kernel is not able mount it's root via NFS, this might have many different reasons. It requires all addresses in the /etc/bootptab file to be correct, and the access rights on the server have to be set correctly - not only in /etc/exports but also the permissions for the directory to get mounted. If that's correct check that a portmapper is running on the server, and that it registered the mountd and nfsd services correctly. You can usually do this by running the command rpcinfo -p Note that services are only listed here if their associated server process is really running. The rpcinfo output should then look something like this: program vers proto port 100000 2 tcp 111 portmapper 100000 2 udp 111 portmapper 100003 2 udp 2049 nfs 100003 2 tcp 2049 nfs 100005 1 udp 663 mountd 100005 1 tcp 665 mountd However, the port numbers might be different. When the kernel starts mounting the NFS root directory it prints out the name of that directory on the server. It should be the same as the one configured in /etc/bootptab. Check that it's correct. If not you can try to use the -d option with mknbi-linux to specify the name explicitely. If the kernel gets an error from the server's nfsd, it prints a number which is defined according to the NFS protocol. The most commonly occurring numbers are: 1 - permission denied to access directory 2 - directory doesn't exist 5 - I/O error on server filesystem 13 - nfsd is unable to access directory 20 - path name is not a directory 63 - path name is too long Note that some nfsd and mountd programs only read /etc/exports on startup. If you changed this file afterwards, you will have to restart both daemons. Additionally, with nfsd versions for Linux earlier than 2.1 you will have problems with special files like UNIX domain sockets or block/character special files on your NFS partitions. You should therefore use the latest avai- lable versions. Problem: The Linux kernel mounts it's root correctly but doesn't give me a login prompt. 1.) This might be the result of an incorrect setup of the root file- system (see No. 2 below). However, it's also possible that your server reported the wrong major/minor numbers for the console device even though you specified them correctly in the NFS mounted root directory. I know of this problem with AIX and HP-UX servers, but there might exist others as well which don't transfer special devices via NFS as Linux requires it. One solution to solve this problem is to boot the diskless client with a ramdisk image as it's root, and then mount the should-be-root directory on the server using NFS. Then you can create the special files in the dev directory using Linux's mknod program, and use the NFS root mounting bootimage again. Another way is to try to find out, how the server operating system encodes major/minor numbers on it's own filesystem. For example, HP-UX uses a 32 bit device number, with the 8 highest bits being the major number, and the lower 24 bits being the minor device number: major << 24 | minor ==> aaaaaaaabbbbbbbbbbbbbbbbbbbbbbbb In this representation (a) means a bit of the major number, and (b) means a bit of the minor number. Linux uses the following scheme instead: major << 8 | minor ==> 0000000000000000aaaaaaaabbbbbbbb The NFS protocol now transfers these 32 bits just as they are, without any further interpretation regarding major/minor numbers. That means, that all relevant bits in the Linux representation fit into the minor number on HP-UX. Therefore, if you create a device on the HP-UX server, you have to alway give it a major number of zero and compute the minor number the way mentioned above for Linux. For example, to let Linux see a device 5/2 in it's NFS-mounted /dev directory, you can compute the minor device number on HP-UX as 5 << 8 | 2 ==> 1282 So the device to create on the HP-UX server is 0/1282. This will let Linux see 5/2 after the filesystem is mounted with NFS. 2.) Another reason for this problem might be that the init process doesn't get started at all. This can be a result of incorrect shared libraries, which the client might see but without a proper ld.so.cache file. Or the shared libraries are not reachable by the client at all. Bruce Janson and Markus Gutschke collected a good list of possibilities, which you should check out: - you do not have a private copy of the /, /etc, /var, ... directories - your /dev directory is missing entries for /dev/zero and/or /dev/null or is sharing device entries from a server that uses different major and minor numbers (i.e. a server that is not running Linux - see above). - your /lib directory is missing libraries (most notably libc* and/or libm*) or does not have the loader files ld*.so* - you neglected to run ldconfig to update /etc/ldconfig.cache or you do not have a configuration file for ldconfig. - your /etc/inittab and/or /etc/rc.d/* files have not been customized for the clients. - your kernel is missing some crucial compile-time feature (such as NFS filesystem support, booting from the net, trans- name (optional), ELF file support, networking support, driver for your ethernet card). - missing init executable (in one of the directories known by the kernel: /etc, /sbin, ?) - missing /etc/inittab - missing /dev/tty? - missing /bin/sh - system programs that insist on creating/writing to files outside of /var (mount and /etc/mtab* is the canonical example) Problem: Can't compile the bootrom Please get in touch with me if you encounter any problems while recompiling the bootrom.