Mulitple WLC Discovery & Join Questions

[padaer2011]

Hi Everyone,

I have a site with an old 5508 WLC that has 45 APs registered currently. I want to build up a new WLC (5520) with new APs registered in advance and switch over wireless clients to it at a time of choosing. To do this, I was planning to have the wireless interface of the new AP disabled so clients can't connect (I will enable 1 AP to test the WLANs and clients in advance) until everything is ready. Then I will disable the wireless interfaces on the old APs and bring it up the new ones. This way it's also possible to switch back to the old wireless quickly enough should there be any problems with the new one. I'll decommission the old WLC after a week or so once happy everything is good. I'm hoping to keep the wireless management interfaces for both WLC in the same vlan as it's cleaner for me in the long run however I'm concerned about old APs registering to the new WLC and visa versa with the new AP and old WLC. I've couple of questions for this scenario surrounding the discovery and join process highlighted in bold below.

To keep the old AP registered to the old WLC, I'm going to set the IP of the primary controller as the old WLC (not set yet) on the existing APs and leave Secondary and Tertiary blank. I think that should keep the old AP registered to the old AP as long as it's reachable? There is a DHCP scope for these AP but no option for WLC IP has been configured.

On the new AP I'm going to prime them with the IP of the new WLC before connecting to the network. My main question here is, in the event of new AP discovering the old WLC also from a broadcast I'm not sure one gets priority in that scenario?

The alternative option I was thinking of was putting the mgmt interface of the new WLC in a different VLAN to the old so I can at least block APs from discovering the wrong WLC with an ACL. I can also specify the IP of each WLC in 2 separate DHCP scopes this way. This is easier to control the APs connecting to the correct WLC but as I mentioned it might be cleaner for me in the long run to keep them in the same vlan for now.

I'm not considering having both WLC in a mobility group as an option currently as there are lots different AP models and different software version on the old. Plus it's a warehouse environment and wireless clients roam at speed on forklifts. I'd need to be certain of the performance of this before going down that route.

That's it. Thanks in advance if anyone can help or has experience with a similar scenario!

[Leo Laohoo]

We use DHCP Option 43. 

Old APs can only join the old WLC.  The old APs cannot join the new WLC because it is running newer codes which does not support the older APs.  

So we have DHCP Option 43 configured for the new WLC and the old WLC. 

When an old AP attempts to join the new WLC, they will get denied and join the old WLC. 

When the new AP joins the new controller they will join.  End of process.

[Arshad Safrulla]

First bring the new WLC up, build a mobility tunnel between old and new controllers. Check the AP compatibility with the new 5520 controllers and also the AireOS version. If all AP's are supported with the new WLC and AireOS, manually change the IP of the primary controller under each AP that you are planning to migrate. Once all AP's are migrated decommission the old WLC. Change the option 43 under DHCP scope to reflect new WLC AP manager interface

FYI. 5520 is announced EOS and EOL. Consider upgrading to new Catalyst controllers.