Setting up Linux DHCP Server with Dynamic DNS Support

This tutorial will explain how to setup DHCP to dynamically update a local DNS server. I use Red Hat/Fedora but these are common steps you'll have to use with just about any flavor of these Linux services.

Setting up the Server

For starters, lets configure the /etc/dhcpd.conf file. It's pretty self explanitory. If you are planning on setting up a local DNS server leave in the 3 lines pertaining to Dynamic DNS, otherwise take them out.

#
# Global Settings
#
 
# Turn on Dynamic DNS:
ddns-domainname "domain.lan";
ddns-update-style interim;
ddns-updates on;
 
# Don't allow clients to update DNS, make the server do it
# based on the hostname passed by the DHCP client:
deny client-updates;
allow unknown-clients;
 
#
# 10.0.0.0/255.255.255.0 Scope Settings
#
subnet 10.0.0.0 netmask 255.255.255.0 {
 
        # Range of DHCP assigned addresses for this scope
        range                           10.0.0.100 10.0.0.200;
        # 1 day
        default-lease-time              86400;
        # 2 days
        max-lease-time                  172800;
 
        # Configure the client's default Gateway:
        option subnet-mask              255.255.255.0;
        option broadcast-address        10.0.0.255;
        option routers                  10.0.0.2;
 
        # Configure the client's DNS settings:
        option domain-name              "domain.lan";
        option domain-name-servers      10.0.0.1;
 
}

Now things get a little tricky. If you have Windows clients you are going to need to modify the /etc/rc.d/init.d/dhcpd file. In the start() directive you should see a line that looks something like

daemon /usr/sbin/dhcpd ${DHCPDARGS}

Comment that out with a # and add in the following lines. If you want, add in the DHCPDARGS also, but I don't really use it.

/sbin/route add -host 255.255.255.255 dev eth0 2> /dev/null
daemon /usr/sbin/dhcpd eth0

Make sure you set the ethx to the network interface you want to serve dhcpd requests on. This is particularly vital if you have a multihomed server.

Setting up the Client

The client needs to send a hostname for this to work correctly. The DHCP server needs to know what hostname to set in DNS. Windows does it by default, however you'll need to make sure your /etc/sysconfig/network-scripts/ifcfg-ethx file looks something like this (with the DHCP_HOSTNAME directive set properly.

# make sure this line is has no settings on it!
DEVICE=eth0
BOOTPROTO=dhcp
HWADDR=01:01:01:01:01:01
ONBOOT=yes
TYPE=Ethernet
DHCP_HOSTNAME=host
USERCTL=no
PEERDNS=yes

Now, you should go have a beer and explain what you just did to your girlfriend.