Question about DHCP Server

[tasherma]

Ok, this has been bugging me for a while. I am confused to how this is working. There is a DHCP Server, originally on Win 2k, then switched to Novell later, but anyway, the DHCP server has different scopes 9.0.0.x, 8.0.0.x, 10.0.0.x and 172.20.2.x

The server is inside the main building, and everything in that building gets a 172.20.2.x address. There are 3 WAN links connected via T1 lines. One of those buildings gets 9.0.0.x addresses, one buiding gets 8.0.0.x and the other one a 10.0.0.x address. But I have looked at the configuration of the server in Win 2k and the newer Novell one, and I don't know how this is working. Someone else set this up. I set up all the clients, however, and I simply enabled DHCP and did not assign any class, which I thought would be needed to do this. So I am guessing there must be a configuration in the routers that tell it what scope to use? There is one router in the main building that is connected to one at each other building. Is there a setting in these cisco routers for this, or is it something on the server that I'm not seeing?

Thanks

 

[jimbopalmer]

in a Nortel Router you can assign any Subnet a DHCP server and convert broadcasts on thet subnet to unicasts to the DHCP server, when it is actually in another subnet. I would imagine this is pretty common.

I tried to remain child-like, all I acheived was childish.

 

[ledzepe]

Yes, it should be in the router.

 

[Comstocb]

DHCP requests are sent out as broadcasts meaning they stop at the layer 3 boundary UNLESS the gateway is enabled to forward the requests to a defined DHCP server. This means that the layer 3 portion of the packet that is now forwarded is modified to have a source address of the router interface for the network that the DHCP request was received on (this is referred to as the relay agents IP address). Since this IP address is on the same network as the client requesting an IP, the DHCP server knows from which scope to issue an IP. this is just a more detailed answer to the ones above which are correct.

Brian

 

[tasherma]

Ok, thanks everyone, especially Brian. Now I understand what's going on