DHCP server & Client

• Objectives– to learn how to setup dhcp servers

• Contents– Download and Install The DHCP Package

– The /etc/dhcpd.conf File

– Upgrading Your DHCP Server

– How to get DHCP started

– Modify Your Routes for DHCP on Linux Server

– Configuring Linux clients to use DHCP

– Simple DHCP TroubleshootingPracticals

– working with TCP/IP utilities and files

Download and Install The DHCP Package

• You have three ways to install DHCP server on RedHat– With yum/up2date (install sample config and prepare lease data base)

– RPM (Simply install it, togeather with sample config)

– You need at least RPM-package dhcp-server if you download manually

– TAR-BALL (Allways latest version, the ISC standard dhcp, manual work)

• Getting the DHCP server with yum– Will download and start configure DHCP

• Installing from RPM’s

• You can also obtain dhcp sources directly from ISC

The version rpm number is dhcp-3.0.2-6 in our example, and 3.0.3 for the tar ball.

# yum install dhcp-server# yum install dhcp-server

# rpm –ivh dhcp-3.0.2-6.i586.rpm# rpm –ivh dhcp-server-3.0.2-6.i586.rpm

# rpm –ivh dhcp-3.0.2-6.i586.rpm# rpm –ivh dhcp-server-3.0.2-6.i586.rpm

# cd /usr/local/src# wget ftp://ftp.isc.org/isc/dhcp/dhcp-3.0.3.tar.gz

# cd /usr/local/src# wget ftp://ftp.isc.org/isc/dhcp/dhcp-3.0.3.tar.gz

• Sample dhcpd.conf file:/usr/share/doc/dhcp-<version-number>/dhcpd.conf.sample

Their version number is dhcp-3.0pl1-23 in this example

• Begin with the sample configuration file

• Basic file format

The /etc/dhcpd.conf File basics

# cp /usr/share/doc/dhcp-3.0pl1-23/dhcpd.conf.sample \  /etc/dhcpd.conf

# cp /usr/share/doc/dhcp-3.0pl1-23/dhcpd.conf.sample \  /etc/dhcpd.conf

subnet 192.168.1.0 netmask 255.255.255.0 { default-lease-time 86400; max-lease-time 86400;option routers 192.168.1.100;option log-servers 192.168.1.100;option broadcast-address 192.168.1.255;option domain-name-servers 192.168.1.100, 80.84.37.3;option nntp-server 192.168.1.100;range 192.168.1.201 192.168.1.220; }

subnet 192.168.1.0 netmask 255.255.255.0 { default-lease-time 86400; max-lease-time 86400;option routers 192.168.1.100;option log-servers 192.168.1.100;option broadcast-address 192.168.1.255;option domain-name-servers 192.168.1.100, 80.84.37.3;option nntp-server 192.168.1.100;range 192.168.1.201 192.168.1.220; }

The /etc/dhcpd.conf File fix/denial

• Deliver fixed address to a host

• Dont do DHCP on all interfaces/subnets if multihomed

• TFTP boot server and boot loader file

subnet 80.84.37.0 netmask 255.255.255.240 { not authoritative; }

subnet 80.84.37.0 netmask 255.255.255.240 { not authoritative; }

host printer { hardware ethernet 00:50:DA:38:CE:23; fixed-address 192.168.1.64; option domain-name-servers 192.168.1.100; option broadcast-address 192.168.1.255; option domain-name "printer.ikea.se";}

host printer { hardware ethernet 00:50:DA:38:CE:23; fixed-address 192.168.1.64; option domain-name-servers 192.168.1.100; option broadcast-address 192.168.1.255; option domain-name "printer.ikea.se";}

next-server 192.168.1.60; # tftp-serverfilename "pxelinux.0"; # bootloaderhost brutebert { hardware ethernet00:B0:D0:39:63:8C; }

next-server 192.168.1.60; # tftp-serverfilename "pxelinux.0"; # bootloaderhost brutebert { hardware ethernet00:B0:D0:39:63:8C; }

Dynamic DNS & DHCP

• This is not the full story, DNS is also needed– You will need a DNS in order to update zonefiles

• Main entries in /etc/dhcpd.conf

• You also need one authorized key to allow updates

• These entries comes before any subnet declaration

authoritative; ddns-update-style interim;ddns-domainname "radio.ing-steen.se";update-static-leases on;

authoritative; ddns-update-style interim;ddns-domainname "radio.ing-steen.se";update-static-leases on;

key "DHCP-UPDATER"{ algorithm HMAC-MD5; secret ”<keydata>";}

key "DHCP-UPDATER"{ algorithm HMAC-MD5; secret ”<keydata>";}

Dynamic DNS & DHCP

• The Forward and Reverse name Zone-files to update– They came after the ddns entries in same file.

– Zones must be specified to the DHCP

• Last comes the standard subnet declaration, like on page 3 with this added to it

zone radio.ing-steen.se.{ primary 172.16.0.5; key DHCP-UPDATER;}

zone radio.ing-steen.se.{ primary 172.16.0.5; key DHCP-UPDATER;}

zone 16.172.in-addr.arpa.{ primary 172.16.0.5; key DHCP-UPDATER;}

zone 16.172.in-addr.arpa.{ primary 172.16.0.5; key DHCP-UPDATER;}

authoritative;get-lease-hostnames true; do-forward-updates true; allow unknown-clients; ddns-updates on;

authoritative;get-lease-hostnames true; do-forward-updates true; allow unknown-clients; ddns-updates on;

Upgrading Your DHCP Server

• When updatingLook in header of sample file: /usr/share7doc/dhcp<version>/dhcpd.conf.sample

Add those lines in your existing /etc/dhcpd.conf file

ddns-update-style interim # Redhat Version 8.0+ignore client-updates # Fedora Core 1+

ddns-update-style interim # Redhat Version 8.0+ignore client-updates # Fedora Core 1+

How to get DHCP started

• DHCPD is depending on /var/lib/dhcp/dhcpd.leasesYou might need to erase existing lease files and create an empty:

dhcpd.leases contain leases database format when in action:

• Starting the dhcpd server

• Stoppinig and Reloading the server

# rm –f /var/lib/dhcp/dhcpd.leases# touch /var/lib/dhcp/dhcpd.leases

# rm –f /var/lib/dhcp/dhcpd.leases# touch /var/lib/dhcp/dhcpd.leases

lease 172.16.0.67 { starts 0 2004/09/05 04:41:09; ends 1 2004/09/06 04:41:09; hardware ethernet 00:0d:93:83:8a:8e; uid 01:00:0d:93:83:8a:8e;}

lease 172.16.0.67 { starts 0 2004/09/05 04:41:09; ends 1 2004/09/06 04:41:09; hardware ethernet 00:0d:93:83:8a:8e; uid 01:00:0d:93:83:8a:8e;}

# chkconfig dhcpd on# chkconfig dhcpd on

# service dhcpd start# service dhcpd stop# service dhcpd restart

# service dhcpd start# service dhcpd stop# service dhcpd restart

Modify Your Routes for DHCP on Linux Server

• Temporary solutionAdd the route to 255.255.255.255 from the command line

If the message 255.255.255.255: Unknown host appears then try adding the following entry to your /etc/hosts file:

Then, try:

• Permanent solution add in /etc/sysconfig/static-routes

If this doesn't work properly try adding the following entry to your /etc/hosts file:

# route add -host dhcp dev eth0# route add -host dhcp dev eth0

# route add -host 255.255.255.255 dev eth0# route add -host 255.255.255.255 dev eth0

255.255.255.255 dhcp255.255.255.255 dhcp

eth0 host 255.255.255.255eth0 host 255.255.255.255

255.255.255.255 dhcp255.255.255.255 dhcp

Summary

• DHCP server is used to deliver IP parameters

• Configuration sit in /etc/dhcpd.conf

• Leases sit in /var/lib/dhcp/dhcpd.leases

• DHCP can deliver boot strap files to diskless

• With options you can deliver many functions

• DHCP server usally run as stand alone server

• Start dhcp server with /etc/init.d/dhcpd start

• Stop dhcp server with /etc/init.d/dhcpd stop

• Reload dhcp server with /etc/init.d/dhcpd restart