multipe dhcp pool via same interface

[Simon Hobson]

Guillaume Vachon wrote:

>I was wondering if the following setup can be done.
>
>I have a Centos4 server with 2 NIC 1 pointing to the WAN and the 
>other to the LAN (eth1 is for LAN) eth1 is already serving a dhcp 
>pool. What I would like to know is if it is possible to configure 
>eth1 to serve a total of 4 pool. Assuming that my network cable will 
>be in a router that is able to redirect the different information.
>
>I hope my question is clear if it is not i am sorry just let me know 
>and i will do my best to give as much information as i can!!

It's not clear what you are asking for, are the four pools to be in 
the same subnet, different subnets on the same wire, or different 
subnets which are the other side of a router ?

The answer in all three cases is yes, the DHCP server can do it, but 
the details differs depending on what you are trying to do.

I think you are asking about the last of these - where some of the 
pools are the other side of a router on different physical networks. 
That is trivially easy to configure :

1) Configure a DHCP Relay Agent (aka BOOTP Helper, aka DHCP Relay) on 
each non-local subnet - non-local meaning not directly connected to 
the DHCP server. This is usually done in the router, but it can in 
fact be in any device which is directly attached to the non-local 
network.

2) Configure a subnet declaration for the subnet.

The rest happens automagically !

Note that a Relay Agent is NOT the same as a simple broadcast packet 
forwarder, it actually modifies the packets before unicasting them to 
the server.


If all you want to do is "have it work" then the above is probably 
all you need to know, but if you want to understand what is happening 
inside then I recommend "The DHCP Handbook" by Ralph Droms and Ted 
Lemon where this and everything else is clearly explained.