My question involves how you should handle a single DHCP server for a multihop network: (in our case) you have one DHCP server and a network with a "row" of routers attached to each other (and only one router attached to the DHCP server). We already looked around but only found some information one a situation like in the picture http://publib.boulder.ibm.com/infocenter/iseries/v5r3/topic/rzakg/rzakg502.gif. (We are not using the iSeries DHCP Server, I'm just using the picture as an example)
So, this situation is with one router; but would it be possible to have a whole network of routers (which are DCHP enabled) behind that first router and still have DHCP working right? And if this is possible, how would the DHCP server know to which subnet it should send its respond (e.g. how would the packet look, …)?
Many thanks in advance,
Glenn
Best Answer
This sounds possible, but it sure seems like you are building something unusual and convoluted. I suspect I might look at alternatives...
This is part of how DHCP operates. A DHCP client starts its request with a broadcast, broadcasts do not cross routers. So a DHCP will only respond to the broadcasts with addresses from a scope that matches the IP address of the interface it was received on.
A special piece of software can be installed on an router called a DHCP agent. You must manually configure the DHCP agent with the IP address(s) of the DHCP server. When the router receives the broadcast on one of its local interfaces the agent accepts it, and then adds the ip address the request was received on, then it forwards that to the DHCP server. The DHCP server is able to to select the correct scope since it knows the address that received the request from the router.
http://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol#DHCP_Relaying
If you cannot install a DHCP agent on your router, then it can be install on other devices on the network.