DHCP fail over address delay

[Bryan Dobson]

Having a strange issue regarding DHCP fail over which I was wondering
anyone else had some across in the past. I have gone over the
configuration and believe everything is set as it should be. The issue
is we have a pair of DHCP servers set in a fail over configuration and
have been seeing excessive delays in IP addresses behind handed out.

The servers are running the same version of DHCP and the time on both
servers is in sync. If the request comes into server1 and it does not
fail over, it will complete the transaction and the user will get an
IP. However, if the request is failed over to server2 I have seen a
delay of sometimes more than an hour.

On server1 we see repeated DHCPDISCOVER to peer until eventually
server1 provides the ACK for the address itself.

server1 failover:

failover peer "dhcp" {
  primary;
  address server1;
  port 51000;
  peer address server2;
  peer port 51000;
  max-response-delay 60;
  max-unacked-updates 10;
  load balance max seconds 3;
  mclt 7200;
  split 128;
}

server2 failover:

failover peer "dhcp" {
  secondary;
  address server2;
  port 51000;
  peer address server1;
  peer port 51000;
  max-response-delay 60;
  max-unacked-updates 10;
  load balance max seconds 3;
}