Wireless Access

I've got two sites where I need to implement L3 redundancy.  My question is do the VLANs or the subnets need to be the same on the two controllers? I know the SSIDs need to be the same but if the SSIDs on the two controllers don't correspond to the same VLANs or subnet, would the clients do DHCP again in the new VLAN or expect the same VLAN/subnet?

The handover can be  very quick and if it is quick enough, the radio does not go down long enough for the client to notice and it will not re-DHCP.

Thanks as always cjoseph. So the VLANs/subnets don't need to be the same, correct? Is there anything else I would need to do other than configuring the Backup LMS address on each controller in the AP System profile?

I have a question on the above: If the VLANs/subnet are not the same on the backup LMS and the clients do not re-DHCP will they not be in the 'wrong subnet' during failover?

Yes, the clients that fail won't work until they release/renew, reboot or disconnect/reconnect.

Thanks olino for the quick reply.

Follow-up:

Could this be then avoided in any way making use of L3 Redundancy?

I'm currently looking at a setup where 2 Mobility Controllers are in 2 different routing domains but both advertise the same subnets. I see this working if all the APs are on controller #1 that VLAN will be active and if that controller fails the AP would all move to the 2nd controller which would then advertise the same subnet since it will activitate the VLAN (which is triggered on the APs joining). However if the AP during fallback are active on both controllers we have a routing issue ...

There is really not a "good" way to do make the clients recover automatically (at least not one that I know of).  You MIGHT be able to get the routing to work properly, but as you say, it might break when not all APs move at the same time.  The best bet is to have L2 redundancy for your controllers and only use L3 to protect against some large outage, such as power in the whole datacenter.

I was thinking along these lines as well. Thanks for confirming this :)