DHCP mini-HOWTO (DHCPd/DHCPcd)
Vladimir Vuksan, vuksan@veus.hr
v2.8, 11 February 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
3.3 RedHat 5.x
3.4 RedHat 4.x and Caldera OpenLinux 1.1/1.2
3.5 Debian
3.6 LinuxPPC and MkLinux
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 1.3.16 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
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.x
DHCPcd configuration under RedHat 5.0+ is really easy. All you need to
do is start the Control Panel by typing
control-panel
� Select "Network Configuration"
� Click on Interfaces
� Click Add
� Select Ethernet
� In the Edit Ethernet/Bus Interface select "Activate interface at
boot time" as well as select DHCP as Interface configuration
protocol
When you are finished go the ``last step''
3.4. RedHat 4.x and Caldera OpenLinux 1.1/1.2
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
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
Following section has been written by R. Shapiro
Versions 0.65 and 0.70 of Yoichi Hariguchi's dhcpcd should work
properly in MkLinux and in linuxppc kernel 2.1.24, 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 linuxppc 2.1.24, 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 linuxppc
2.1.24, the warning mentioned above is an indication that the routing
is ready.
For later linuxppc kernels, no version of the Hariguchi dhcpcd will
work: you must use Sergei Viznyuk's version instead (current release
is 1.3.9: see above for url). Unfortunately the Viznyuk dhcpcd is
written for glibc 2, which linuxppc 2.1.1xx isn't. As a result,
compiling it is a bit tricky - contact me for details. Once compiled,
however, it works fine on late kernels (and not at all in MkLinux or
linuxppc 2.1.24).
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:
______________________________________________________________________
MkLinux: Hariguchi: yes; Viznyuk, no
2.1.24: Hariguchi: yes if patched (easy to build); Viznyuk: no
2.1.102+: Hariguchi: no; Viznyuk: yes (tricky to build)
______________________________________________________________________
Note that the Viznyuk dhcpcd writes into /etc/resolv.conf directly
(after renaming the existing one), so there's no need to copy or link
it from /etc/dhcpc. Also note that it's typically installed into
/sbin, not /usr/sbin, and that the command lines options are slightly
different from the Hariguchi version. These differences may require
small changes to ifup, if you're starting dhcpcd that way.
If you want a precompiled dhcpcd for linuxppc, send mail to
reshapiro@mediaone.net.
I've also made binary RPMs available in
Don't use dhcpcd-1.3.8-2.ppc.rpm in that directory, it's broken. The
reliable versions here are dhcpcd-0.70-0.ppc.rpm (for linuxppc
2.1.24), and dhcpcd-1.3.8-3.ppc.rpm (linuxppc 2.1.102 and up). An rpm
for 1.3.9 should show up shortly. I also have a modified 1.3.9 which
includes the -c command-file option, as in 0.65 and 0.70 (the standard
Viznyuk dhcpcd doesn't include this.)
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-${DEVICE}.pid ];
Now sit back and enjoy :-).
3.9. Various notes
Following step(s) are not necessary but might be useful to some people
a) If you need network connectivity only occasionally you can start
dhcpcd from the command line (you have to be root to do this) with:
/usr/sbin/dhcpcd
When you need to down (turn off) the network type
/usr/sbin/dhcpcd -k
3.10. Troubleshooting
If you have followed the steps outlined above and you are unable to
access the network there are several possible explanations:
I. Your network card is not configured properly.
During the boot up process your Linux will probe your network card and
should say something along these lines:
______________________________________________________________________
eth0: 3c509 at 0x300 tag 1, 10baseT port, address 00 20 af ee 11 11, IRQ 10.
3c509.c:1.07 6/15/95 becker@cesdis.gsfc.nasa.gov
______________________________________________________________________
If a message like this doesn't appear your ethernet card might not be
recognized by your Linux system. If you have a generic ethernet card
(a NE2000 clone) you should have received a disk with DOS utilities
that you can use to set up the card. Try playing with IRQs until Linux
recognizes your card (IRQ 9,10,12 are usually good).
II. Your DHCP server supports RFC 1541/My DHCP server is Windows NT
Try running dhcpcd by typing
dhcpcd -r
Use ifconfig to check if your network interface is configured (wait
few seconds for the configuration process, initally it will say
Inet.addr=0.0.0.0)
If this solves your problem add the "-r" flag to the boot up scripts
ie. instead of /sbin/dhcpcd you will have /sbin/dhcpcd -r
For example under RedHat edit script /etc/sysconfig/network-
scripts/ifup and change the following
______________________________________________________________________
IFNAME=$[ {DEVICE} \
"/sbin/dhcpcd -r -c /etc/"- etc etc.
______________________________________________________________________
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.