WLC Deployment Guidelines (Connect to Redundant Switches)

Unanswered Question
May 30th, 2008

Hello All,

Can I just ask, is it common practice to connect, lets say, a 4404 WLC to a pair of switches (lets say distribution) so if a switch fails, the WLC remains available. I understand that if you were using LAG, it would have to be to the same physical switch.

I was thinking, if you had a 4404, have two ports configured to one switch 1 in a lag, and the other two ports configured in a lag to switch 2.

Is this OK?

Many thx for the advice as always :)

Kind regards,

Ken

I have this problem too.
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Scott Fella Fri, 05/30/2008 - 08:41

Won't work that way... If you use lag, all the wlc ports need to be on a single etherchannel. What you have to do is not use lag and configure each port with an ap-manager interface. This way you should be able to split the ports and define what your primary and secondary ports will be used.

jeromehenry_2 Fri, 05/30/2008 - 09:37

There is 1 3750 model on which you can split your LAG. That is, on the controller you still create only one LAG (you can't create more than 1 as Fella explains, it's an on or off type of feature), 2 links go to the first 3750, 2 others to the second, and a link between switches ensures consistency.

Not a good or recommended design though. If you lose your switch, you probably lose along with it a good part of your network anyway. LAG relies on the idea that redundancy is built by having space on a backup controller.

Having a AP Manager per port, therefore physical links to different switches, is another possibility, but it has also some other limitations (load balancing system)... I try to use LAG and controller backup whenever it is possible...

Scott Fella Fri, 05/30/2008 - 10:13

Jerome is correct about the 3750 using cross stack etherchannel. Or if your core chassis is running VSS you can do that also.

Cisco mentions this: Do not configure a LAG connection that spans across multiple switches. When you use LAG, it must be with all ports that belong to the same EtherChannel that goes to the same physical switch

But who knows if this was released before the cross stack or VSS.

kfarrington Sat, 05/31/2008 - 02:18

Thx guys for the input.

So the recommended design is NOT to have a WLC across two switches (LAG or not). Correct?

And use the backup controller as the redunacny for the wireless infrastructure, ie N+N and N=1 etc etc

Is this correct?

Many thx once again,

Ken

Scott Fella Sat, 05/31/2008 - 05:19

I would have to say yes.... that is the recommended best practice. If you can afford to have antoher controller, then split up the ap's on both wlc's. You can also place all ap's on one wlc and let the other controller be your backup. Either way, you can have the backup wlc on a different switch in case the other switch fails.

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