Fwd: Query on Usage of ISC DHCP Server

[Simon Hobson]

Naresh Kumar wrote:


>If in case there is a relay agent in between the DHCP server and the 
>client, and let say DHCP server and the DHCP client are in the same 
>subnet and the relay agent is in the different subnet, with what ip 
>address will the DHCP request from the relay agent be identified by 
>the DHCP server? Will the request packet be identified with the 
>clients ip or the relay agent's ip?

To be clear, the client and server are on DIFFERENT physical 
networks, but both networks are using the SAME IP subnet ?
This will **NOT** work - it is a broken IP configuration. Don't even 
waste your time trying, just fix the IP setup.

Rule number one of IP addressing - all addresses must be unique. 
Ideally globally unique but that went out of the window many years 
ago with NAT*, but within the scope of your network (in this case, 
the DHCP server, client, and relay agent) they should be locally 
unique.

* NAT == Broken. Fundamentally, NAT breaks rules number one of IP 
addressing and is an ugly cludge that breaks many things.


>If request packet is identified by relay agent IP ( which is not in 
>DHCP server's subnet and relay agent ip is not configured in pools), 
>Does ISC DHCP Server process request and allocates IP address ?

The relay agent IP must be in the same IP subnet as the client, OR in 
an IP subnet which is defined as a shared-network with the client. 
The server (any DHCP server, not just ISCs) uses the Gateway IP 
address to determine the location of the client. It will look for a 
subnet declaration containing the Gateway IP, and then allocate an IP 
address from any available range in that subnet (or in any subnet in 
the shared-network section in the case of shared-networks).

But, this will **NOT** work if a subnet is both remote and local to 
the server, as appears to be the case with your setup.
-- 
Simon Hobson

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