DHCP Authorizing Subnets - dhcp-3.1.1

Simon Hobson dhcp1 at thehobsons.co.uk
Mon May 25 12:27:22 UTC 2009

<rohit.gupta3 at wipro.com> wrote:

>I have a doubt relating to the following scenario.
>Is it possible to make DHCP proxy /server  independent of IP address 
>being used by MN / client ?

I will repeat the question again, if you want useful help, then I 
suggest you explain what it is you are trying to achieve or what is 
not working for you. If you explain this, then we might be able to 
offer useful help - so far you have not given enough information to 
allow us to do that.

Based on what you have asked so far, I can only guess at what you are 
trying to do - and my guess is that you want the clients to be in a 
different subnet to the relay agent.

If this is the case, then yes you can do that with some limitations.

The first issue is that the server need to be able to identify the 
network location of any client. This is an absolute MUST since the 
server cannot correctly allocate an address if it does not know which 
network the client is attached to. If the client is not "local" to 
the server (ie attached to a network to which the server has a direct 
attachment), then the server uses the Gateway Interface Address 
(GIAddr) to work this out. So the GIAddr of the relay agent MUST be 
on the same network as the client.

This does not mean that the GIAddr must be in the same subnet as the 
client, but if it isn't then the server must be configured with a 
shared-network statement enclosing the subnets used by the client and 
relay agent.

The other limitation is that both the client and relay agent 
addresses must be fully routable between them and the server. This 
also means that the GIAddr (and it's subnet) must be unique across 
the whole network served by the DHCP server.

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
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