Failover on a large DHCP system

John Wobus jw354 at
Fri May 8 21:17:53 UTC 2009

On May 7, 2009, at 10:30 AM, Nicholas F Miller wrote:
> We have a large DHCP instance which is currently running 304 
> shared-network definitions and 677 pools. We would like to implement 
> DHCP failover but are a little worried about the overhead needed to 
> implement it on such a large DHCP network. Will the servers be 
> overwhelmed trying to keep things in sync with so many pools?
> Also, can we reload configs without restarting DHCP yet?
> _________________________________________________________
> Nicholas Miller, ITS, University of Colorado at Boulder

We use failover and avoid using omshell by reconfiguring and restarting 
the daemon once every 2 minutes
(if there is a config change). It generally works well (we've been 
doing it for years), and failover actually aids coverage since we 
stop/start the
two servers one after the other.  In general, though, if there are any 
bugs that somewhat-rarely causes problems when you restart
the daemon, we see them, given all our restarts.  I believe there are 
other sites that do pretty much the same thing.

I might consider omshell, but haven't because (1) we've been doing this 
and it works, i.e., inertia; (2) rumors of its demise;
and (3) I like having our config all in one file: we use short leases, 
so our entire lease file is short-term data that we don't
worry about losing: even if we lost both lease files, it would not be 
much of a disaster for us.

 > grep -c pool dhcpd.conf
 > grep -c shared dhcpd.conf
 > grep -c host dhcpd.conf

John Wobus
Cornell University IT Systems&Operations

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