Configure DHCPd to Work on Certain NIC(s)

Your server has more than one network interfaces and you need DHCP server to associated with only one of them.

Here is how you configure it on Ubuntu:

# File: /etc/default/dhcp3-server
INTERFACES="eth0"
or
INTERFACES="eth0 eth1"

Onn Redhat/Fedora/Centos:
# File: /etc/sysconfig/dhcpd
DHCPDARGS=eth1
or
DHCPDARGS="eth0 eth1"

Reference:
http://www.centos.org/docs/5/html/Deployment_Guide-en-US/s1-dhcp-configuring-server.html