dhcp-users Digest, Vol 31, Issue 8

Chris Buxton chris.p.buxton at gmail.com
Wed May 4 16:01:50 UTC 2011

On May 4, 2011, at 5:49 AM, Benjamin wrote:
> I have three network (separated with router):
> Network A: DHCP server, a relay and my client
> Network B: interconnection netwok between A and C
> Network C: An other DHCP server
> I make this setup to test "fault tolerance" (sorry I'm french and I don't know if you understand "fault tolerance" ...)

The term 'fault tolerance' is correct and is understood.

> So when my DHCP A is offline, the relay relaye my request to the DHCP C . All is OK. but if I set back online my DHCP A, my client still uses the DHCP C (because my XP client record the first IP Adress and  when I do a release/renew, he request this old IP, so my DHCP C send an 'ACK' for this IP)
> But if I can put a delay in the relay agent, my client request the old IP adress, but the DHCP A will propose a new IP and the client will accept it.

That's not correct. The renewal does not go through the relay. Instead, it is unicast back to the DHCP server. It is difficult to break the association between client and DHCP server once a lease is active without changing routing, putting up a firewall, or taking down a DHCP server.

Chris Buxton
BlueCat Networks

More information about the dhcp-users mailing list