From LQWiki

DHCP (Dynamic Host Configuration Protocol) is a protocol which enables the dynamic assignment of IP addresses to devices on a network.

Getting a DHCP address

When computers get an IP address by DHCP, they run a daemon (dhcpcd) that keeps track of things.

Restarting DHCP

If your network interface goes down, you might need to restart the DHCP daemon.

Three daemons that do this are: dhclient, dhcpcd, and pump. Like so...

Fedora

  dhclient

Suse 9

  dhcpcd -i eth0

Distro Configuration

Debian

  dpkg --reconfigure etherconf

Slackware

  netconfig