dhcp with multiple dhcp-relay routers

[mjones at mnsi.net]

Good morning

 

              We have a setup with clients behind two routers doing VRRP for
their gateway.   Both of these routers are also doing DHCP relay to a single
freeradius 3.0 server acting as a dhcp server.

 

              So when a client initates the dhcp process after booting up,
both routers see the request and relay it to the server.   Both requests
arrives at the server at almost the same time.  The only difference in the
two requests is the giaddr or gatewau ip addr.

 

              The dhcp server processes each request separately as it
should. The first one to get the reply back to the client is the one that it
uses.  All this is a expected and normal.

 

              The situation we are having is in the sqlippool.   When the
process for each request looks up to see if the client has an active lease
only one of the requests will match the previous lease as it is comparing
the giaddr and not just the key.  So depending on which response gets back
to the client first they either get the ip they had or a new ip.

 

              We see a few possible solutions to this from our perspective.

 

1.	Some how ignore or modify the giaddr to be the VRRP address instead
of the fixed ip.   We have already tried doing this on the roiuters and
there is no support for this.
2.	Delay the responses for one of the relay routers so it is only used
if the primary router has failed.

 

There maybe something completely obvious we are missing here, any help would
be appreciated.

 

 

Mark Jones

Operations

Managed Network Systems

Windsor Desk 519-258-2333 x8417

Cell 226-340-1254