Failover : Balancing a one-ip pool (!)

Chris Buxton clists at
Tue Feb 16 14:28:38 UTC 2016


I have a couple of thoughts about this.

1. When using a hub-and-spoke architecture, I find its better to let the spokes be primary and the hub be secondary for all its peers.

2. Singleton pools like you're describing don't really work for the failover protocol. Only the primary server will ever be able to answer. You won't see any benefit in terms of load balancing or even fault tolerance. You're better off configuring these without failover; if you really can't use reservations (host declarations with fixed addresses), then just define each singleton pool identically on each server, without failover (as long as you're certain there will never be two clients asking for that one address).


> On Feb 16, 2016, at 12:05 AM, Nicolas Ecarnot <nicolas at> wrote:
> Hello,
> This message is less a question than a discussion, because we're happy with our setup for years and maybe won't change soon, unless you answer with a nice new idea.
> We have 7 DHCP servers in a star pattern : one central and 6 around.
> The center is the primary peer for the others, for around 400 pools and lots of subnets.
> Around 30 pools are classical ones, and balancing fine.
> The numerous other ones are one-ip pools.
> These one-ip pools are made this way in order to :
> - benefit from failover setup. There seems to be no other way, failover can only be setup on pools
> - apply classID rules by pool, working only on one machine by subnet. We don't want to use static reservations for that.
> All this is working like a charm, but a small concern of mine is the periodic balancing (60 seconds by default, we raised it to 120) where I see that the servers are trying and obviously failing to balance the only one ip between peers.
> This is not very bad, except it is eating CPU and flooding the logs.
> But I post here this message in hope someone could advice a better way to do. Because I read lots of doc about balancing and the way ISC DHCPD is managing this sounds clever and I'd be happy to use it in a proper way.
> Of course, external constraints exist forcing me to use this weird one-ip pools setup. But I'll fight to change them if someone replies with nice hints I may have missed.
> Regards,
> -- 
> Nicolas ECARNOT
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