DHCP Relay Agent

As DHCP works primarily via network broadcasts, it will only work if both the client and the server is located on the same network segment. Unless you have a Relay Agent set up, that is.

A DHCP Relay Agent is a small server that resides on one of the hosts (or directly on the router) on the client's segment, listening for DHCP requests, and forwarding them transparently to the DHCP server on the other LAN.

Since the different LANs have their own series of IP addresses, the DHCP server needs to be set up with a separate scope for each LAN served.

I would point out that one should be careful about routers that are configured to propagate directed broadcasts; this can result in the DHCP server getting two DHCP requests.

This can cause the Wonderful and Famous problem where people's telnet sessions get dropped for no apparent reason. (Although the problem manifestation is in no way limited to telnet sessions getting boinked off.)

So whazzup with that? The user loses connectivity in this scenario when the client enters the DHCP RENEWING state, it contacts the DHCP server that issued its DHCP lease. Some DHCP servers (not all) will get very confused if they get a second request for the same IP number; and they will NACK one of the requests. This results in your client temporarily losing its lease, and getting it back pretty much immediately. However, when the stack loses its IP address, the telnet session gets reset.

Lovely, eh? Caveat implementor.