DHCP server on a different subnet

Glenn Satchell glenn.satchell at uniq.com.au
Thu May 12 06:20:24 UTC 2011

> On 05/11/11 11:21, Alex Bligh wrote:
>> --On 11 May 2011 23:04:27 +1000 Glenn Satchell
>> <glenn.satchell at uniq.com.au> wrote:
>>> Sounds like it should work just fine. This is standard behaviour for
>>> remote subnets, for example. You can't always configure the dhcp server
>>> to have an interface on every subnet it serves.
>> Thanks. I am familiar with remote subnets but they tend to use a proxy.
>> I am not using a proxy but relying on having an interface on the same
>> broadcast domain but not the same subnet. I can't see how a reasonable
>> client could differentiate this from a proxy, but as we all know not
>> all clients do reasonable things!
> That is the purpose of the proxy.  To be on the same network and when
> relaying the DHCP request identify to the DHCP server what subnet it
> came from.
> DHCP relay is normally handled by the router(default gateway)
> But if an interface is on the same broadcast domain, but on a different
> subnet, how will that interface determine what subnet the broadcast
> packet came from?  I don't think it can.
> Lyle Giese
> LCR Computer Services, Inc.
You are right, the server can't. This is a "shared-network" and the dhcp
server will allocate an address from one of the pools in the shared
network. But without some way of distinguishing the requests, eg some sort
of class membership or fixed-address in the server configuration it will
pseudo-randomly assign from one of the pools.


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