DHCP server failover behind relay

Vadym Abramchuk abramm at gmail.com
Wed Sep 5 20:32:04 UTC 2012

2012/9/5 Simon Hobson <dhcp1 at thehobsons.co.uk>

> Vadym Abramchuk wrote:
>  Failover setup for isc-dhcpd is a well-known, however, both server and
>> clients MUST be in the same subnet
> Wrong
>  So build-in failover does not work for relays.
> Wrong
> You just need to configure your relay agents to forward to both servers.
> This can either be by sending two unicast packets (add two server
> addresses), or (I believe) if the network allows, sending one directed
> broadcast.

Unfortunally, none of my relay agents can send packets to both servers. So
that statements above are right for me :).
As for broadcast, I've tried setting the relay's server address to (broadcast of my servers subnet). dhcpd accepts DISCOVERs, but
the OFFERs do not reach the client. Nice try, anyway.

Let's accept the axiom that I can't deliver requests to both servers. Is
there any other way? Chaining to second relay agent which will duplicate
requests to both servers looks awfull.


Vadym Abramchuk
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