Assign from Pool according to Relay Agent

Simon Hobson dhcp1 at
Wed Jul 29 14:46:43 UTC 2015

Patrick Trapp <ptrapp at> wrote:

>> We have got a special need for a stupid router. The router is acting as a DHCP relay agent. However it sends the same address for the DHCP Discovery source IP and GIADDR fields. 
>> So I need a way to say for example; if GIADDR equals to then assign IP addreses from this pool. But that pool is not in the same subnet with the GIADDR. Is it possible at all? I couldn't find any relevant answer to this..

Just to be clear, the example is the IP of the router interface facing the DHCP server, not an IP of an interface facing the clients ?

> Just off the cuff, but are you needing a shared-network declaration? We have requests coming from one network to the DHCP server that are actually for a second (or third) network. We have an empty declaration for the apparent source network as part of a shared-network included with the actual networks that the DHCP server is providing addresses for.

That would probably do it, create a dummy subnet that includes and put it in a shared network with the real client facing subnet. However, this is likely to break things if there are any other routers who's IPs fall into that dummy subnet.

Of course, the real answer is to send the broken router back and insist the vendor fix it !

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