Is there anything new on the DHCP Failover Horizon?

Chris Buxton chris.p.buxton at
Sun Apr 17 03:05:24 UTC 2011

When it happens, use omshell to put the remaining server into
partner-down state, instead of just communications-interrupted.

Write a script that polls dhcpd every few minutes (via omshell)
looking for communications-interrupted, and reacts by putting it into
partner-down. Probably want to put some extra failsafe logic in there,
too, to make sure the problem isn't something else instead.

Chris Buxton
BlueCat Networks

On 4/15/11, Martin McCormick <martin at> wrote:
> 	We have been using DHCP failover for several years and
> like the fact that one server can die and no phones ring for a
> while, at least.
> 	The problems have been when the real world that never
> fails to prove the old saying that if anything can go wrong, it
> will, springs one of its little surprises such as wireless
> controllers that end up sending different data to both servers
> or, as we had today, weather-induced power hits that appear to
> have brought down one server while the other one stayed up but
> in a "peer holds all free leases" lock-down state.
> 	That has caused some staff members to ask whether
> failover really buys us any redundancy. I know it does when
> things fail cleanly such as when one server's dhcpd process dies
> or the power goes away cleanly from a box but I was asked to see
> if there are any other failover strategies that might be in
> consideration that self-heal a bit faster.
> 	The discussions almost always start when we discover
> that one server in the pair hagone in to "peer holds all free
> leases" condition and people are not getting leases. Is there a
> rapid way to clear it, when discovered?
> 	Of course, the real cure is to not send different data
> to both servers. We serve around 10,000 clients here and can go
> for months without a single "peer holds all" messages, but when
> something goes wrong, we get a situation that at least with one
> DHCP server does not monkey-wrench the whole subnet.
> 	Telling everyone that it is only that one subnet, etc,
> is a hard sell. The voices just get louder and the questions
> more probing.
> 	Any ideas as to the best way to handle "no free leases"
> are appreciated as I have never found anything that was really
> clean since the condition that causes it is by nature an error
> and dhcpd is simply trying to be as safe as possible.
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