Multi-server pool question.

Simon Hobson dhcp1 at
Fri Feb 13 12:36:49 UTC 2009

Phill Harvey-Smith wrote:

>We run three DHCP servers on our departmental Linux machines which 
>hand out addresses for some 500+ machines, laptops and printers.
>Up until now we have statically assigned IP addresses to MAC 
>addresses in the dhcp.conf file. This has the advantage that no 
>un-registered host will get an IP addresss, which helps to prevent 
>un-authorised computers being used on our network.
>However recently we have been running short of IP addresses so would 
>like to move over to pool asigned IPs for the laptop machines, as it 
>is unlikley that these will all be connected at once, we intend to 
>leave the printers and desktop machines statically assigned.
>I have worked out how to do this, and have this working in a test 
>environment, however, I can see that having a pool of addresses 
>assigned by multiple servers could cause problems with one server 
>assigning an address to one machine and another server assigning the 
>same address to a different machine.

Correct, you must NOT do this. You will have a lot of collisions, end 
eventually you will find all the servers with their addresses marked 
as abandoned.

>Is there a way that I can resolve this issue, bu configuring the 
>servers to share pool information, or will I have to reserve 
>allocation of the pool addresses to only one of the servers but let 
>the others also manage the statically assigned ones.

Three options come to mind :

1) Split your pool and have part of it served by each server. If any 
server goes down, then the addresses served by it will not be 

2) Run two (and only two) servers as a failover pair. Both servers 
can issue addresses from the pool, but they will communicate with 
each other to avoid conflicts. If one fails, the other can run the 
whole pool.

3) As you suggest, just have one server handling the dynamic pool.

Also, note that you must NOT have any statically assigned address 
(via host statement) that is also in a dynamic pool..

Simon Hobson

Visit for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

More information about the dhcp-users mailing list