dhcp with two relay agents

Glenn Satchell Glenn.Satchell at uniq.com.au
Thu Oct 30 11:45:27 UTC 2008


>Subject: Re: dhcp with two relay agents
>From: fadey <fadey at scancom.es>
>To: dhcp-users at isc.org
>Date: Thu, 30 Oct 2008 10:42:44 +0100
>
>Thanks. It starts getting more clear. Basically now my question narrows
>down to following:
>
>I have this setup:
>
>shared-network router1 {
>  subnet router1.cable_modems {deny unknown-clients; ...}
>  subnet router1.emtas {deny unknown-clients; ...}
>  subnet router1.hosts1 {...}
>  subnet router1.hosts2 {...}
>}
>
>shared-network router2 {
>  subnet router2.cable_modems {deny unknown-clients; ...}
>  subnet router2.emtas {deny unknown-clients; ...}
>  subnet router2.hosts1 {...}
>}
>
>All router1 subnets share the same physical network. The same is true
>for router2 subnets.
>
>Now there is a DHCPDISCOVER relayed from router2 with GIADDR set to
>router2.cable_modems IP. It is an unknown-client (mac is not explicitly
>specified in dhcpd.conf). In this case will dhcpd be "smart enough" to
>DHCPOFFER an IP from route2.hosts1 subnet and NOT from router1.hosts*
>subnets? 
>
Yes. That's exactly how it is meant to work. dhcpd sees that giaddr
comes from the subnet within the particular shared-network and offers
from an appropriate range.

regards,
-glenn

>
>> fadey wrote:
>> >Thanks for your reply. I was trying to simplify my network setup and
>> >messed it up :-)
>> >
>> >I'm in a cable network. Behind every router I have about 3-5 different
>> >networks. Thats why I use shared-network option:
>> >
>> >shared-network eth1 {
>> >   subnet that.is.on.networkcard1 {...}
>> >   subnet router1.cable_modems {...}
>> >   subnet router1.emtas {...}
>> >   subnet router1.hosts1 {...}
>> >   subnet router1.hosts2 {...}
>> >}
>> 
>> You do NOT need a local network card for each remote subnet. Try this :
>> shared-network eth1 {
>>    subnet router1.cable_modems {...}
>>    subnet router1.emtas {...}
>>    subnet router1.hosts1 {...}
>>    subnet router1.hosts2 {...}
>> }
>> 
>> Make a shared network for EACH SHARED NETWORK. A shared network is 
>> one where ON THE SAME BIT OF WIRE you have multiple subnets. So the 
>> stuff behind router1 is NOT on a shared network with stuff behind 
>> router2 or with stuff connected directly to the server.
>
>



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