DHCP server.......cisco router........!!

Unanswered Question


Can i just have two routers working as DHCP server in one LAN scenario, such that one router acting as primary and second one as failover to the primary router? Just wondering if i can have redundancy in dhcp server as well.

Moreover, if I have a windows server acting as DHCP server, can i have router acting as dhcp server(secondary) as well. just in case primary is down router can act as dhcp server.


I have this problem too.
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Istvan_Rabai Tue, 03/11/2008 - 22:44

Hi Gaurav,

Yes you can.

If they both respond to hosts, the hosts will decide which dhcp offer to accept.

When your dhcp servers are located more than 1 hop away, then you can configure several "ip helper address" commands in the dhcp relay agent, the 1st command pointing to the 1st dhcp server, the 2nd command pointing to the backup dhcp server.



royalblues Wed, 03/12/2008 - 01:58

Redundancy with DHCP servers are generally done in the following way

create two scopes on two seperate servers. On one server say A, create an exclusion that covers the first half of the scope. On the second server exclude the second half of the scope. This prevents one server from allocating addresses from the other server; and also stops one server from sending out NAKs to DHCP requests/renews intended for the other server.



Richard Burts Wed, 03/12/2008 - 04:32


Both Istvan and Narayan have focused their answers on the part of your question about having 2 DHCP servers (whether it is 2 routers or 1 router and 1 external server). Let me focus on the other part of your question which is about having 1 server as primary and the other server as backup. You can not really do this. Both servers will be active. Both servers will receive the DHCP request and both servers will offer addresses. As mentioned by Istvan the client will choose which address to accept.

So yes you can have 2 DHCP servers to provide redundancy. But no you can not really have one as backup to function only if the primary fails. They will both be active all the time.




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