Configuring a SLES DHCP failover

In most networks DHCP is one of the single-point-of-failures. If DHCP failes, every devices relying on DHCP cannot function.

In order to  provide a high availability to your DHCP server, set up a backup DHCP server running the same Linux distribution and version, as follows:

1. Stop DHCP on both DHCP servers (rcdhcpd stop).
2. On your primary DHCP server, add lines to the /etc/dhcpd.conf file, similar to following example:

   failover peer "dhcp" {
      primary;
      address 192.168.1.10;          # local host IP address
      port 647;                      # make sure this port is not used by other
                                       programs
      peer address 192.168.1.11;     # backup host IP address
      peer port 647;
      max-response-delay 60;
      max-unacked-updates 10;
      mclt 600;
      split 128;
      load balance max seconds 3;
   }
   include "/etc/dhcpd.master";

   On your backup DHCP server, add lines to the /etc/dhcpd.conf file, similar to following example:

   failover peer "dhcp" {
      secondary;
      address 192.168.1.11;         # local host IP address
      port 647;                     # make sure this port is not used by other
                                      programs
      peer address 192.168.1.10;    # primary host IP address
      peer port 647;
      max-response-delay 60;
      max-unacked-updates 10;
   }
   include "/etc/dhcpd.master";

3. Add the following lines to the end of /etc/dhcpd.master on both DHCP servers. On SUSE Linux Enterprise Server, copy this file to /var/lib/dhcp/etc.

   subnet 192.168.1.0 netmask 255.255.255.0 {
     pool {
       failover peer "dhcp";
       range 192.168.1.100 192.168.1.200;
       deny dynamic bootp clients;
     }
     option routers 192.168.1.1;
   }

4. Start DHCP on both DHCP servers (rcdhcpd start.

After these configurations are complete, the primary DHCP server, which is usually a management server or install server, responds to DHCP client requests. If the primary DHCP server goes offline, the backup DHCP server automatically takes its place and provides DHCP service.