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DHCP mini-HOWTO (DHCPd/DHCPcd) Vladimir Vuksan, vuksan@veus.hr v2.5, 18 September 1998 This document attempts to answer basic questions on how to setup your Linux box to serve as a DHCP server or a DHCP client. ______________________________________________________________________ Table of Contents 1. Introduction 1.1 Standard Disclaimer 1.2 New Versions of this Document 1.3 Feedback 1.4 Contributors 1.5 Copyright Information 2. DHCP protocol 3. Client Setup 3.1 Downloading Client Daemon 3.2 Slackware setup 3.3 RedHat 5.0 and up setup 3.4 RedHat 4.x and Caldera OpenLinux 1.1 setup 3.5 Debian 1.3.1 setup 3.6 LinuxPPC and MkLinux setup 3.7 Token Ring networks 3.8 Tying it all together 3.9 Various notes 3.10 Troubleshooting 4. DHCP Server Setup 4.1 DHCP server for UNIX 4.2 Network Configuration. 4.3 Options for DHCPd 4.4 Starting the server ______________________________________________________________________ 1. Introduction 1.1. Standard Disclaimer No liability for the contents of this documents can be accepted. Use the concepts, examples and other content at your own risk. As this is a new edition of this document, there may be errors and inaccuracies, that may of course be damaging to your system. Proceed with caution, and although this is highly unlikely, I don't take any responsibility for that. Also bear in mind that this is NOT official information. Much content in this document are assumptions, which appear to work for people. Use the information at your own risk. 1.2. New Versions of this Document New versions of this document will be periodically posted to comp.os.linux.answers. They will also be added to the various anonymous FTP sites who archive such information, including: In addition, you should generally be able to find this document on the Linux Documentation Project page via: 1.3. Feedback Feedback is most certaintly welcome for this document. Without your submissions and input, this document wouldn't exist. So, please post your additions, comments and criticisms to vuksan@veus.hr. 1.4. Contributors This document has been modified from the original version by Paul Makeev. The following people have contributed to this mini-HOWTO. ╖ Heiko Schlittermann ╖ Jonathan Smith ╖ Dan Khabaza ╖ Hal Sadofsky ╖ Henrik Stoerner ╖ Paul Rossington 1.5. Copyright Information This document is copyrighted (c)1998 Vladimir Vuksan and distributed under the following terms: ╖ Linux HOWTO documents may be reproduced and distributed in whole or in part, in any medium physical or electronic, as long as this copyright notice is retained on all copies. Commercial redistribution is allowed and encouraged; however, the author would like to be notified of any such distributions. ╖ All translations, derivative works, or aggregate works incorporating any Linux HOWTO documents must be covered under this copyright notice. That is, you may not produce a derivative work from a HOWTO and impose additional restrictions on its distribution. Exceptions to these rules may be granted under certain conditions; please contact the Linux HOWTO coordinator at the address given below. ╖ If you have questions, please contact the Linux HOWTO coordinator at linux-howto@sunsite.unc.edu 2. DHCP protocol DHCP is Dynamic Host Configuration Protocol. It is used to control vital networking parameters of hosts (running clients) with the help of a server. DHCP is backward compatible with BOOTP. For more information see RFC 2131 (old RFC 1531) and other. (See Internet Resources section at the end of the document). You can also read DHCP FAQ (http://web.syr.edu/ jmwobus/comfaqs/dhcp.faq.html). This mini-HOWTO covers both the DHCP _SERVER_ daemon as well as DHCP _CLIENT_ daemon. Most people need the client daemon which is used by workstations to obtain network information from a remote server. The server daemon is used by system administrators to distribute network information to clients so if you are just a regular user you need the _CLIENT_ daemon. 3. Client Setup 3.1. Downloading Client Daemon 2.0.x kernels No matter what distribution you are using you will need to download the DHCP client daemon for Linux. The package you need to download is called dhcpcd and the current version is 0.70. You can read the description of the package here. (ftp://sunsite.unc.edu/pub/Linux/system/network/daemons/dhcpcd-0.70.lsm) 2.1.x kernels Due to changes in ipv4 network package in 2.1.x kernels (e.g. way it sets the defaults for several fields) dhcpcd doesn't work properly. Most users don't run experimental kernels so this shouldn't be a problem. If you do you should try dhcpcd 1.3.6 which is a modified version that has been written by Sergei Viznyuk sergei@phystech.com in order to avoid mentioned problems. You can fetch it at: ╖ ╖ 3.2. Slackware setup You can download the latest copy of the DHCPcd from any sunsite mirror or following: ╖ ╖ ╖ (Primary site in Japan) Download the latest version of dhcpcd.tar.gz ╖ Unpack it tar -zxvf dhcpcd-0.70.tar.gz ╖ cd into the directory and make dhcpcd cd dhcpcd-0.70 make ╖ Install it (you have to run the following command as root) make install This will create the directory /etc/dhcpc where DHCPcd will store the DHCP information and dhcpcd file will be copied into /usr/sbin. In order to make the system initialize using DHCP during boot type: cd /etc/rc.d mv rc.inet1 rc.inet1.OLD This will move the old network initialization script into rc.inet1.OLD. You now need to create the new rc.inet1 script. Following code is all you need: ______________________________________________________________________ #!/bin/sh # # rc.inet1 This shell script boots up the base INET system. HOSTNAME=`cat /etc/HOSTNAME` #This is probably not necessary but I #will leave it in anyways # Attach the loopback device. /sbin/ifconfig lo 127.0.0.1 /sbin/route add -net 127.0.0.0 netmask 255.0.0.0 lo # IF YOU HAVE AN ETHERNET CONNECTION, use these lines below to configure the # eth0 interface. If you're only using loopback or SLIP, don't include the # rest of the lines in this file. /usr/sbin/dhcpcd ______________________________________________________________________ Save it and reboot your computer. When you are finished go the ``last step'' 3.3. RedHat 5.0 and up setup DHCPcd configuration under RedHat 5.0+ is really easy. All you need to do is start the Control Panel by typing control-panel Then select "Network Configuration" and under ethernet (usually eth0) interface define DHCP as your protocol. Other parameters should be left blank. When you are finished go the ``last step'' 3.4. RedHat 4.x and Caldera OpenLinux 1.1 setup DHCPcd is included in the standard RedHat distribution as an RPM and you can find it on your distribution's CD-ROM in RPMS directory or you can download it from: and install it with rpm -i dhcpcd-0.6-2.i386.rpm Alternatively you can compile your own version by following the steps outlined in the Slackware. This information was provided to me by nothing nothing@cc.gatech.edu ______________________________________________________________________ Removed my static ip and name from /etc/resolv.conf. However, I did leave in the search line and my two nameserver lines (for some reason my dhcpcd never creates a /etc/dhcpc/resolv.conf, so I have to use a static /etc/resolv.conf). In /etc/sysconfig/network I removed the HOSTNAME and GATEWAY entries. I left the other entries as is (NETWORKING, DOMAINNAME, GATEWAYDEV). In /etc/sysconfig/network-scripts/ifcfg-eth0 I removed the IPADDR, NETMASK, NETWORK, and BROADCAST entries. I left DEVICE and ONBOOT as is. I changed the BOOTPROTO line to BOOTPROTO=dhcp. Save the file. Reboot your computer. ______________________________________________________________________ When you are finished go the ``last step'' 3.5. Debian 1.3.1 setup There is a deb package of DHCPcd at or you can follow the Slackware installation instructions. To unpack the deb package type dpkg -i /where/ever/your/debian/packages/are/dhcpd*deb It appears that there isn't a need for any DHCPcd configuration because: From: Heiko Schlittermann (heiko@os.inf.tu-dresden.de) The dhcpcd package installs it's startup script as usual for debian packages in /etc/init.d/<package_name>, here as /etc/init.d/dhcpcd, and links this to the various /etc/rc?.d/ directories. The contents of the /etc/rc?.d/ dirs is then executed at boot time. If you don't reboot after installing you should consider starting the daemon manually: /etc/init.d/dhcpcd start When you are finished go the ``last step'' 3.6. LinuxPPC and MkLinux setup Following section has been written by R. Shapiro Versions 0.65 and 0.70 of Yoichi Hariguchi's dhcpcd should work properly for both variants of linux on ppc, with the following caveats: * If you want, or need, to build the executable from sources, note that the ppc linux compilers assume that 'char' is 'unsigned char' while the Hariguchi sources assume 'char' is 'signed char'. To build from sources you must edit the Makefile so that CFLAGS includes the option "-fsigned-char". * The current stable release of linuxppc [aka linux-pmac] is 2.1.24 and requires the 2.1 patch (http://www.cro.net/ vuksan/dhcppatch). Both the DR2.1 and DR3.0 releases of mklinux use a 2.0 kernel (2.0.33) and do not require this patch, although it's harmless to apply it. Note that the dhcpcd rpm on the linuxppc cd-rom does not include the 2.1 patch and therefore will not work with the linux on that cd! It will work with mklinux however. * In the linuxppc 2.1 kernels, you'll see a router warning shortly after dhcpcd starts up. You can ignore this. * The Hariguchi dhcpcd takes awhile, about 30 seconds, to make its initial connection to the server and to set up routing. In the 2.1 linuxppc kernels, the warning mentioned above is an indication that the routing is ready. In mklinux, you'll have to keep checking netstat -r to find out. As far as Viznyuk's version of dhcpcd is concerned I have a Viznyuk dhcpcd (v1.3.7) executable that works in recent linuxppc kernels: 2.1.102, 103, 115, and 119 have been tested. It's possible to build this from sources, but I don't know the details. The Viznyuk dhcpcd doesn't work in 2.1.24, but in that kernel the patched Hariguchi dhcpcd works. The Hariguchi dhcpcd can be built easily from sources. Short summary: ______________________________________________________________________ 2.1.24: Hariguchi: yes if patched (easy to build); Viznyuk: no 2.1.102+: Hariguchi: no; Viznyuk: yes (tricky to build) ______________________________________________________________________ Once dhcpcd is installed, do the following in addition to the resolv.conf issue mentioned in ``last step''. ╖ Delete or rename /etc/sysconfig/network-scripts/ifcfg-eth0 ╖ Remove everything from /etc/sysconfig/network except NETWORKING and, if you have a fixed symbolic name, HOSTNAME If you want a precompiled 0.70 dhcpcd for linuxppc 2.1 kernels, send mail to reshapiro@mediaone.net. 3.7. Token Ring networks If you are trying to run dhcpcd on the Token Ring Network it will not work. This is the solution provided to me by Henrik Stoerner (henrik_stoerner@olicom.dk) The problem is that dhcpcd only knows about Ethernet cards. If it finds a Token-Ring card, it refuses to do anything with it and reports "interface is not ethernet". The solution is to apply a simple patch to the dhcpcd sources. I have put up a small web page with the patch, RedHat RPM-files and a precompiled binary at The patch has been sent to the dhcpcd maintainer, so hopefully it will be included in a future release of dhcpcd. 3.8. Tying it all together After your machine reboots your network interface should be configured. Type: ifconfig You should get something like this ______________________________________________________________________ lo Link encap:Local Loopback inet addr:127.0.0.1 Bcast:127.255.255.255 Mask:255.0.0.0 UP BROADCAST LOOPBACK RUNNING MTU:3584 Metric:1 RX packets:302 errors:0 dropped:0 overruns:0 frame:0 TX packets:302 errors:0 dropped:0 overruns:0 carrier:0 coll:0 eth0 Link encap:Ethernet HWaddr 00:20:AF:EE:05:45 inet addr:24.128.53.102 Bcast:24.128.53.255 Mask:255.255.254.0 ^^^^^^^^^^^^^^^^^^^^^^^ UP BROADCAST NOTRAILERS RUNNING MULTICAST MTU:1500 Metric:1 RX packets:24783 errors:1 dropped:1 overruns:0 frame:1 TX packets:11598 errors:0 dropped:0 overruns:0 carrier:0 coll:96 Interrupt:10 Base address:0x300 ______________________________________________________________________ If you have some normal number under inet. addr you are set. If you see 0.0.0.0 don't despair, it is a temporary setting before dhcpcd acquires the IP address. If even after few minutes you are seeing 0.0.0.0 please check out ``troubleshooting''. DHCPcd is a daemon and will stay running as long as you have your machine on. Every three hours it will contact the DHCP server and try to renew the IP address lease. It will log all the messages in the syslog (on Slackware /var/adm/syslog, RedHat/OpenLinux /var/log/syslog). One final thing. You need to specify your nameservers. There are two ways to do it, you can either ask your provider to provide you with the addresses of your name server and then put those in the /etc/resolv.conf or DHCPcd will obtain the list from the DHCP server and will build a resolv.conf in /etc/dhcpc. I decided to use DHCPcds resolv.conf by doing the following: Back up your old /etc/resolv.conf mv /etc/resolv.conf /etc/resolv.conf.OLD If directory /etc/dhcpc doesn't exist create it mkdir /etc/dhcpc Make a link from /etc/dhcpc/resolv.conf to /etc/resolv.conf ln -s /etc/dhcpc/resolv.conf /etc/resolv.conf If that doesn't work try this (fix suggested by nothing@cc.gatech.edu with a little amendment by Henrik Stoerner) This last step I had to perform only because my dhcpcd doesn't create an /etc/dhcpc/resolv.conf. In /etc/sysconfig/network-scripts/ifup I made the following changes (which are a very poor hack, but they work for me): ______________________________________________________________________ elif [ "$BOOTPROTO" = dhcp -a "$ISALIAS" = no ]; then echo -n "Using DHCP for ${DEVICE}... " /sbin/dhcpcd -c /etc/sysconfig/network-scripts/ifdhcpc-done ${DEVICE} echo "echo \$$ > /var/run/dhcp-wait-${DEVICE}.pid; exec sleep 30" | sh if [ -f /var/run/dhcp-wait-${DEVICE}.pid ]; then ^^^^ echo "failed." exit 1 ______________________________________________________________________ I changed to: ______________________________________________________________________ elif [ "$BOOTPROTO" = dhcp -a "$ISALIAS" = no ]; then echo -n "Using DHCP for ${DEVICE}... " /sbin/dhcpcd echo "echo \$$ > /var/run/dhcp-wait-${DEVICE}.pid; exec sleep 30" | sh if [ ! -f /var/run/dhcp-wait-${DEVICE}.pid ]; then ^^^^^^ echo "failed." exit 1 ______________________________________________________________________ Notice the ! (bang) in if [ ! -f /var/run/dhcp-wait-${DEVICE}.pid ]; Now sit back and enjoy :-). 3.9. Various notes Following step(s) are not necessary but might be useful to some people a) If you need network connectivity only occasionally you can start dhcpcd from the command line (you have to be root to do this) with: /usr/sbin/dhcpcd When you need to down (turn off) the network type /usr/sbin/dhcpcd -k 3.10. Troubleshooting If you have followed the steps outlined above and you are unable to access the network there are several possible explanations: I. Your network card is not configured properly. During the boot up process your Linux will probe your network card and should say something along these lines: ______________________________________________________________________ eth0: 3c509 at 0x300 tag 1, 10baseT port, address 00 20 af ee 11 11, IRQ 10. 3c509.c:1.07 6/15/95 becker@cesdis.gsfc.nasa.gov ______________________________________________________________________ If a message like this doesn't appear your ethernet card might not be recognized by your Linux system. If you have a generic ethernet card (a NE2000 clone) you should have received a disk with DOS utilities that you can use to set up the card. Try playing with IRQs until Linux recognizes your card (IRQ 9,10,12 are usually good). II. Your DHCP server supports RFC 1541 Try running dhcpcd by typing dhcpcd -r Use ifconfig to check if your network interface is configured (wait few seconds for the configuration process, initally it will say Inet.addr=0.0.0.0) If this solves your problem add the "-r" flag to the boot up scripts ie. instead of /sbin/dhcpcd you will have /sbin/dhcpcd -r III. During bootup I get error message "Using DHCP for eth0 ... failed" but my system works fine. You are most likely using RedHat and you haven't followed instructions carefully :-). You are missing the ! (bang) in one of the if statements. Jump ``here'' and check how to fix it. IV. My network works for few minutes and then stops responding There are some reports of gated (gateway daemon) screwing up routing on Linux boxes which results in problem described above. Check if gated is running ps -auxww | grep gate If it is try removing it with RedHat's RPM manager or removing the entry in /etc/rc.d/ V. My ethernet card is recognized during boot up but I still get "NO DHCPOFFER" message in my logs. I also happen to have a PCMCIA ethernet card. You need to make sure that you have the 10BaseT port ("phone" plug) on your network card activated. Best way to verify it is to check what kind of connector your card is configured for during bootup e.g. ______________________________________________________________________ eth0: 3c509 at 0x300 tag 1, 10baseT port, address 00 20 af ee 11 11, IRQ 10. ^^^^^^^^^^^^ 3c509.c:1.07 6/15/95 becker@cesdis.gsfc.nasa.gov ______________________________________________________________________ I have received reports of laptop users having this kind of problems due to the PCMCIA utilities (specifically ifport) that would set the connector type to 10Base2 (thinnet). You have to make sure you use 10BaseT for your connection. If you are not reconfigure the card and restart the computer. VI. My DHCP client broadcasts requests but no one answers (Contributed by Peter Amstutz) On some systems, you need to include some hostname for your machine as part of the request. With dhcpcd, do this with 'dhcpcd -h foohost' Probably the hostname wanted will be your account username on the network. VII. I have followed all the steps but still my machine is not able to connect The cable modem will usually memorize the ethernet address of your network card so if you connect a new computer or switch network cards you will somehow have to "teach" your cable modem to recognize the new computer/card. Usually you can turn of the modem and bring it back up while computer is on or you will have to call tech support and tell them that you have changed a network card in the computer. You have firewall rules (ipfwadm rules) that disallow port 67/68 traffic used by DHCP to distribute configuration info. Check your firewall rules carefully. VIII. I have MediaOne Express service and I still can't connect. It appears that MediaOne has been using adding some things to DHCP that shouldn't be there. Supposedly this is not a problem anymore but if you experience outages check for these things. If you are (un)lucky to have Windows NT on your machine if you go into Event Viewer you will see a warning like this. DHCP received an unknown option 067 of length 005. The raw option data is given below. 0000: 62 61 73 69 63 basic If this is the problem go to and either download a binary or get the source for the change. 4. DHCP Server Setup 4.1. DHCP server for UNIX There are several DHCP servers available for U*X-like OSes, both commercial and free. One of the more popular free DHCP servers is Paul Vixie/ISC DHCPd. Currently the latest version is 1.0 (suggested for most users) but 2.0 is in beta testing. You can get them from After you download it you need to unpack it. After you do cd into the distribution directory and type: ./configure It will take some time to configure the settings. After it is done type: make and make install 4.2. Network Configuration. When done with installation type ifconfig -a. You should see something like this: ______________________________________________________________________ eth0 Link encap:10Mbps Ethernet HWaddr 00:C0:4F:D3:C4:62 inet addr:183.217.19.43 Bcast:183.217.19.255 Mask:255.255.255.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:2875542 errors:0 dropped:0 overruns:0 TX packets:218647 errors:0 dropped:0 overruns:0 Interrupt:11 Base address:0x210 ______________________________________________________________________ If it doesn't say MULTICAST you should reconfigure your kernel and add multicast support. On most systems you will not need to do this. Next step is to add route for 255.255.255.255. Quoted from DHCPd README: "In order for dhcpd to work correctly with picky DHCP clients (e.g., Windows 95), it must be able to send packets with an IP destination address of 255.255.255.255. Unfortunately, Linux insists on changing 255.255.255.255 into the local subnet broadcast address (here, that's 192.5.5.223). This results in a DHCP protocol violation, and while many DHCP clients don't notice the problem, some (e.g., all Microsoft DHCP clients) do. Clients that have this problem will appear not to see DHCPOFFER messages from the server." Type: route add -host 255.255.255.255 dev eth0 If you get a message "255.255.255.255: Unknown host" You should try adding the following entry to your /etc/hosts file: 255.255.255.255 all-ones Then, try: route add -host all-ones dev eth0 or route add -net 255.255.255.0 dev eth0 eth0 is of course the name of the network device you are using. If it differs change appropriately. 4.3. Options for DHCPd Now you need to configure DHCPd. In order to do this you will have to create or edit /etc/dhcpd.conf. Most commonly what you want to do is assign IP addresses randomly. This can be done with settings as follows ______________________________________________________________________ default-lease-time 600; max-lease-time 7200; option subnet-mask 255.255.255.0; option broadcast-address 192.168.1.255; option routers 192.168.1.254; option domain-name-servers 192.168.1.1, 192.168.1.2; option domain-name "mydomain.org"; subnet 192.168.1.0 netmask 255.255.255.0 { range 192.168.1.10 192.168.1.100; range 192.168.1.150 192.168.1.200; } ______________________________________________________________________ This will result in DHCP server giving a client an IP address from the range 192.168.1.10-192.168.1.100 or 192.168.1.150-192.168.1.200. It will lease an IP address for 600 seconds if the client doesn't ask for specific time frame. Otherwise the maximum (allowed) lease will be 7200 seconds. The server will also "advise" the client that it should use 255.255.255.0 as its subnet mask, 192.168.1.255 as its broadcast address, 192.168.1.254 as the router/gateway and 192.168.1.1 and 192.168.1.2 as its DNS servers. You can also assign specific IP addresses based on clients ethernet address e.g. ______________________________________________________________________ host haagen { hardware ethernet 08:00:2b:4c:59:23; fixed-address 192.168.1.222; } ______________________________________________________________________ This will assign IP address 192.168.1.222 to a client with ethernet address 08:00:2b:4c:59:23. You can also mix and match e.g. you can have certain clients getting "static" IP addresses (e.g. servers) and others being alloted dynamic IPs (e.g. mobile users with laptops). There are a number of other options e.g. wins server addresses, time server etc., if you need any of those options please read the dhcpd.conf man page. 4.4. Starting the server You can now invoke the DHCP server. Simply type (or include in the bootup scripts) /usr/sbin/dhcpd If you want to verify that everything is working fine you should first turn on the debugging mode and put the server in foreground. You can do this by typing /usr/sbin/dhcpd -d -f Then boot up one of your clients and check out the console of your server. You will see a number of debugging messages coming up.