Failover peer outside pools?

Graham Clinch g.clinch at
Thu Nov 5 10:40:05 UTC 2015

Hi Nicolas,

> I saw that in some rare cases, we have some subnets with *no* pool, thus
> *no* failover setup, where there's just one static reservation declared,
> and it is working.
> But I was wondering how it goes?
> - when the host is requesting some DHCP traffic, it is broadcasted via
> the router towards 2 DHCP server that have no idea about what the other
> did some hours ago in this subnet
> - as the only request is about a static ip, I guess any of both server
> is answering correctly, but not telling the other.

Assuming both servers have the same configuration for the static
allocations, all is good.  In fact, your dhcpd.leases file will only
ever contain leases that were dynamically assigned by the server (i.e.
from a 'range'), because the configuration file already defines all the
information required to correctly match a client to a 'host'
fixed-address (and although the server advertises a lease time to the
client, it doesn't bother recording that expiry time, because when even
when the lease expires, the address is still restricted to just that

> So I'm embarrassed that the router is broadcasting the DHCP traffic to 2
> servers that don't talk (about this particular subnet - there are
> chatting about others).
> The documentation seems to imply that failover definition lies only
> inside pools.
> I could create a pool just to add failover context, but the same doc
> also states that static reservation should stay outside pools.

For networks without any dynamic addresses, we don't bother generating
an empty pool (I seem to remember that empty pools are considered a
configuration error).

The 'RESERVED LEASES' section of dhcpd.conf's manpage might be
interesting reading?

In short, I don't think there is anything wrong with your configuration.


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