Failure of dhcp server failover

[Simon Hobson]

Eugene Grosbein <eugen at grosbein.net> wrote:

> I've switched my single address pools to non-failover mode and the problem has gone. Case closed.

Just to finish this up for the benefit of anyone searching the archives later ...

What I think was happening in this case is that with only one address in a pool, failover just "doesn't work properly". Only one server can hold that lease, and if it decides to load balance* the query to the other server then neither will reply to the client - one server doesn't reply because it's going to leave the other one to do it, but the other one doesn't reply because it hasn't got a free lease.

This would appear to be just a corner case where the people who designed and built the failover system didn't envisage it being used for very very small (in this case, one address) pools. In any pool with 2 or more free addresses this wouldn't be a problem as the free leases would be balanced between the peers and both would have at least one free lease.

And the answer in this case was to realise that there's no need for failover when a single address pool is tied to a specific client - and as is done with host statements, simply put the same (non-failover) config on both servers.


* Perhaps someone with greater knowledge of how the load balancing works could check. I suspect the decision is done on a simple hash, and it's pot luck whether the server with the free lease will get to answer the query.