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Contributor II
Posts: 56
Registered: ‎12-17-2011

L3 redundancy - LMS/Backup LMS

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?

Guru Elite
Posts: 20,821
Registered: ‎03-29-2007

Re: L3 redundancy - LMS/Backup LMS

 

 

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.



Colin Joseph
Aruba Customer Engineering

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Contributor II
Posts: 56
Registered: ‎12-17-2011

Re: L3 redundancy - LMS/Backup LMS

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?

Guru Elite
Posts: 20,821
Registered: ‎03-29-2007

Re: L3 redundancy - LMS/Backup LMS

Do not need to be the same. Backup lms is all you need.


Colin Joseph
Aruba Customer Engineering

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Occasional Contributor II
Posts: 13
Registered: ‎11-06-2012

Re: L3 redundancy - LMS/Backup LMS

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?

Aruba Employee
Posts: 664
Registered: ‎04-15-2009

Re: L3 redundancy - LMS/Backup LMS

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

Occasional Contributor II
Posts: 13
Registered: ‎11-06-2012

Re: L3 redundancy - LMS/Backup LMS

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 ...

 

 

Aruba Employee
Posts: 664
Registered: ‎04-15-2009

Re: L3 redundancy - LMS/Backup LMS

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.

Occasional Contributor II
Posts: 13
Registered: ‎11-06-2012

Re: L3 redundancy - LMS/Backup LMS

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

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