Fail over serves on different VLANS

Patrick Trapp ptrapp at
Thu Jan 14 12:54:35 UTC 2016

Actually, observing network captures in our network, I usually see paired offers - different addresses, one from each server - and the querying host picks one and acknowledges it. The other offer expires and gets sent out again in response to a different request.

I don't think moving your second host to a new VLAN should necessarily be cause for concern as long as the two servers can communicate with each other.

Better to test to be sure, of course.

> On Jan 14, 2016, at 6:18 AM, Klaus Vink Slott <gqv604 at> wrote:
> Hi
> We have been running 2 dhcp servers in fail over configuration for quite a while. Now we consider moving one server to a host in another building. This will also place the host on another VLAN.
> In a earlier tread here John Wobus <jw354 at> wrote:
> > As far as I know, DHCP redundancy works by having the servers
> > offer different addresses and the client picking one. ISC
> > DHCP servers reduce the obvious duplicated effort by having
> > one of the two DHCP servers wait a few seconds to see if the
> > other server makes an offer. But if the one server doesn't
> > pick up on it's peer's offer, the address it offers itself
> > is always a different one.
> How does the server "see if the other server makes an offer". Do they need to bee on the same VLAN or is it communicated directly between the servers?
> -- 
> Regards
> Klaus Vink Slott
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