DHCP failover setup with several relay agents
Robert Blayzor
rblayzor.bulk at inoc.net
Mon Sep 22 14:10:59 UTC 2008
We have a set of DHCP servers setup now that properly work in a
failover setup. (best we can tell)
In reading the docs and a lot of posts on the list, it seems as if
this type of setup only works with local LAN based broadcast setups
where the servers can see all requests coming in.
In our setup, we have no local broadcast DHCP clients and all of our
requests come pointed to one server IP address from different DHCP
relay agents (ie: Cisco routers).
The question is, can a DHCP failover setup work for relay agents if
requests are only directed at one server? Now, I know that this is
not the perfect failover setup, as if the primary failed, the agents
would have to be directed toward the working server. This can easily
be fixed with the L3 switch we have in front of the servers that can
direct traffic for a virtual IP instead of the physical IP's if the
active server fails.
I think the problem is however that if we just keep sending all
requests to one server, the IP pools will be "half" of what they
normally are because the "failover" setup is actually a "load balanced
with failover" setup. If that's the case then would it be safe to
assume them that failover only properly works in a broadcast based
environment only?
Would it make more sense in this type of setup to just run one active
server and use something like rsync to send the leases file over to a
secondary "standby" server? I was hoping that in DHCP failover one
could actually be a primary and one could be a standby, but from the
docs, it doesn't sound like that will work because the secondary unit
will hold half of the available leases per pool.
--
Robert Blayzor, BOFH
INOC, LLC
rblayzor at inoc.net
http://www.inoc.net/~rblayzor/
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