20.3 DHCP in a Cluster

The Dynamic Host Configuration Protocol (DHCP) provides a mechanism whereby a system can be presented with an IP address dynamically. This is usually (but not necessarily) done at boot time. If you have a DSL connection to the Network, you are probably getting an IP address through DHCP sent to your PC as you boot it. The address is probably different each time you boot.

The cluster cannot function as a DHCP client because clusters require static addresses, but it can function as a DHCP server. The server will have access to a database that identifies the pool of IP addresses to be loaned out and identifies the legitimate clients. The cluster will function as a DHCP server and also provide failover capabilities through CAA.

 # caa_stat -t dhcp Name     Type         Target      State         Host ------------------------------------------------------------ dhcp     application  ONLINE      ONLINE        sheridan

Since the DHCP database will be available to all members of the cluster through the magic of CFS, it is relatively easy for CAA to handle the failover if necessary.

All DHCP clients must request access to the DHCP server using the default cluster alias in order to avoid having to reconfigure the DHCP software each time the serving member leaves the cluster.