Updating dhcpd.conf on a failover pair

David Coulthart davec at columbia.edu
Thu Sep 16 21:35:07 UTC 2010

Currently we operate a pair of DHCP servers (4.1.1-P1) using the failover protocol.  We restart them once an hour to apply configuration changes.  However, we don't do anything to make sure we only restart one server at a time.  I'm thinking I need to at least add a 60 second sleep between restarting each server and probably really need to look into some sort of script to check the failover state using OMAPI.  The real reason for this email, however, is I'm wondering what the implications are when a failover pair are operating with differing configurations, even if it's only for 60 seconds or so.

Most of the time our configuration changes only involve changes to a subclass of client MAC addresses, which I doubt has any significant impact on the failover protocol.  However, it's possible that at any time the configuration changes could involve the addition/modification/removal of shared networks, subnets or pools.  How does the failover protocol handle inconsistencies between the two servers in any of these areas?   Does this have any implications for how these changes should be activated without causing an outage for the users?  What about reducing the time necessary for the servers to synchronize themselves?

I found an old thread about this issue:


with some suggestions based on experience, but I haven't found any official documentation or word from the developers.

Dave C.

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