dhcp-users Digest, Vol 31, Issue 8

Benjamin hexor38 at gmail.com
Wed May 4 12:49:54 UTC 2011

> Can you clarify your setup, and what the actual problem is ?
> Clients do not "choose" a relay or server, they simply broadcast
> requests and *ALL* relays and servers will receive it. Some may
> choose to ignore it for some reason, but all will receive it.
> So if you have two relay agents serving a network, or a relay agent
> in the same network as the server, then the server(s) will receive
> more than one copy of a broadcast request. That is normal.
> Once a client has an active lease then it will periodically attempt
> to renew it. These renewals, while the lease is still active, are
> initially made by unicast to the server that issued the lease - and
> relay agents don't get involved, neither do other DHCP servers. If
> the issuing server doesn't respond, the client will eventually fall
> back to broadcasting a renewal request and other relay agents&
> servers then get involved.

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" ...)

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.

Sorry for my english,

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