Multiple subnets with relays

David McKen david.mcken at
Mon Jan 19 13:17:28 UTC 2009

If you have multiple shared-subnet definitions the DHCP server looks at 
the relay agent's ip and matches it up with one of the subnet 
definitions, once that is done then all subnets under that shared-subnet 
definition become valid for that request and normal "full-pool" 
mechanics take effect.

That is my understanding of the matter, thus far have a network of 10+ 
shared network definitions and this works great.

Jessica Meyer wrote:
> Dear Simon,
> Thank you for your answer.
>> Congratulations, your config is just what you need (apart from adding
>> a few options like routers etc). The rest is automagic - the server
>> spots that the GIAddr (Gateway Interface Address) field is filled in
>> and uses it to determine which subnet (or shared network) the client
>> is connected to.
> Glad I'm on the right way, _BUT_, as you can see, I've set a
> shared-network for and, but how does DHCPD know to
> give out IPs from this two networks?? I know that if a request comes
> from, DHCPD gives out an address of the range (in
> this case, from to But what I want is that, if
> the first range has no more addresses, DHCPD also gives out addresses
> from the network (even if the relay is Hope I
> could explain it.
> In the end, I will create some shared-networks, but I want to know
> where I can set explicitely which relays get which ranges etc.
> Greetings
> Jess
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