How to setup Linux as DHCP client

Disclaimer: The information contained herein is NOT official information of any kind and there are no warranties to the accuracy of the data. All information is provided in good faith. Use at your own risk.

Vladimir Vuksan, vuksan@veus.hr
v 2.1, Last revised: October 11th, 1997

Introduction

This HOWTO explains how to setup your Linux system to work in a DHCP environment as a client (DHCPcd). If you are looking for a DHCP server you need to read DHCPd mini-HOWTO at http://sunsite.unc.edu/LDP/HOWTO/mini/DHCPd. DHCP is a protocol that allows a client machine to obtain network information from a server. Many organizations are starting to use it because it eases network administration especially in large networks or networks which have lots of mobile users. DHCP is also being heavily used by cable Internet service provider such as MediaOne Express, Time Warner etc.
More info about DHCP can be found in DHCP FAQ.

Road Runner Service

If you have Road Runner cable service check out http://people.qualcomm.com/karn/rr/index.html. If that doesn't solve your problem try following.

2.1.x kernels

If you are running a > 2.1.30 kernel (don't remember the exact number and www.linuxhq.com is down currently) you might encounter a problem with the dhcpc. According to Dan Khabaza:
"The changes are due to differences in ipv4 network package, in the way it sets the defaults for several fields."

Dan has provided a patch for it that can be obtained at http://www.cro.net/~vuksan/dhcppatch. To apply it just copy it to the dhcpcd source directory (instruction how to get source are in the following section) and type

patch < dhcppatch

dhcpcd should compile cleanly after the patch has been applied.

Method

Step 1) 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 0.65. The description of the package reads:

Title:          dhcpcd
Version:        0.65
Entered-date:   05MAY97
Description:    dhcpcd is an RFC2131 compliant DHCP client daemon. It
                gets an IP address and other information from a
                corresponding DHCP server, configures the network
                interface automatically, and tries to renew the lease
                time according to RFC2131. It works in the RFC1541
                compliant mode when the '-r' option is specified.
                So far it is found that dhcpcd 0.65 works fine with the
                following DHCP servers:
                  1. ISC's dhcpd-BETA-5.15
                  2. DHCP server on Windows NT server 3.51
                  3. DHCP server version 1.3b by WIDE project.
                  4. DHCP server in the SolarNet PC-Admin 1.5 package
                  5. DHCP server used in the Time Warner Cable's
                     Internet Access Service
                See the "Changes" file if you want to know the difference
                from the previous version.
Keywords:       DHCP, client, Linux
Author:         yoichi@fore.com (Yoichi Hariguchi)
Maintained-by:  yoichi@fore.com (Yoichi Hariguchi)
Primary-site:   ftp.kobe-u.ac.jp:/pub/PC-UNIX/Linux/network/dhcp
                33kB dhcpcd-0.65.tar.gz
Alternate-site: sunsite.unc.edu:/pub/Linux/system/network/daemons
                33kB dhcpcd-0.65.tar.gz
Original-site:  
Platforms:       Linux 1.2.xx, 1.3.xx, 2.0.x
Copying-policy: GPL

Note: Support for Bell Atlantic ADSL modems has been announced for
version 0.7.

Slackware

You can download the latest copy of the DHCPcd from any sunsite mirror or following:

ftp://ftp.cdrom.com/pub/linux/sunsite/system/network/daemons/.

ftp://sunsite.unc.edu/pub/Linux/system/network/daemons

ftp://ftp.kobe-u.ac.jp/pub/PC-UNIX/Linux/network/dhcp (Primary site in Japan)

Download the latest version of dhcpcd.tar.gz

Unpack it

tar -zxvf dhcpcd-0.65.tar.gz

cd into the directory

cd dhcpcd-0.65

make

You need to be root to do the following

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. Now skip to Step 2

RedHat

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:

ftp://tsx-11.mit.edu/pub/linux/distributions/redhat/redhat-4.2/i386/RedHat/RPMS/dhcpcd-0.6-2.i386.rpm.

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 part. When done go to Step 2

Debian

There is deb package of DHCPcd at

ftp://ftp.debian.org/debian/stable/binary/net/

or you can follow the Slackware installation instructions.

In order to unpack the deb package type

dpkg -i /where/ever/your/debian/packages/are/dhcpd*deb

When done go to Step 2

Step 2)

Following step(s) are depended on your needs.

a) If you need network connectivity only occasionally you can start dhcpcd from the command line (you need to be root to execute it) by typing

/usr/sbin/dhcpcd

When you need to down (turn off) the network type

/usr/sbin/dhcpcd -k

You now only lack nameservers configuration file (/etc/resolv.conf). For instructions on how to create a resolv.conf go to Step 3

b) If you want (need) network connectivity all the time and would like dhcpcd to start at boot time follow the steps below.

Slackware

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. It should look as follows:

#!/bin/sh
#
# rc.inet1      This shell script boots up the base INET system.
#
# Version:      @(#)/etc/rc.d/rc.inet1  1.01    05/27/93
#

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 the above file as rc.inet1. Reboot your computer. Go to Step 3.

RedHat

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 and go to Step 3

Debian

It appears that there isn't a need for any DHCPcd configuration because:

From: Heiko Schlittermann

The dhcpcd package installs it's startup script as usual for debian packages in /etc/init.d/, 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

Go to Step 3.

Step 3) This step should be the same for all distributions.

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. 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 to the syslog (on Slackware /var/adm/syslog) if you need to check up on it.

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)

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-${DEVICE}.pid ]; then
        echo "failed."
        exit 1
    else
        rm -f /var/run/dhcp-wait-${DEVICE}.pid
        echo "done."
        IPSETUP=yes
    fi
fi

################################# 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-${DEVICE}.pid ]; then
#       echo "failed."
#       exit 1
#    else
#       rm -f /var/run/dhcp-wait-${DEVICE}.pid
#       echo "done."
        IPSETUP=yes
#    fi
fi

#################################

Now sit back and enjoy :-).

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 gotten 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)

Thanks to all the people that contributed with their ideas and suggestions:

Heiko Schlittermann (heiko@os.inf.tu-dresden.de)
Jonathan Smith (jps2@ra.msstate.edu)
Dan Khabaza (danyh@iil.intel.com)
Hal Sadofsky (sadofsky@math.uoregon.edu)