Roaming between WLCs and Mobility Groups

Mitrixsen · ‎07-02-2025

Hello, everyone.

I need some clarification regarding roaming. My book says that:

If two controllers are assigned to different mobility groups, clients can still roam between them, but the roam is not very efficient. Credentials are not cached and shared, so clients must go through a full authentication during the roam.

My other book states that

Client roaming can occur between controllers that are in different mobility groups as long as the controllers are in the same mobility domain. If a client moves from one controller to another in a different mobility domain (that is, to a controller that is not known by the controller that the client leaves), the client has to reauthenticate, reassociate, and get new IP address information.

Please, how exactly does seamless roaming happen? I feel like the explanations of these two books conflict a bit. Do the two WLCs need to be part of the same mobility group in order for credentials to be cached, etc? Or do they just have to be a part of the same mobility domain, or how is it please?

Thank you
David

Leo Laohoo · ‎07-02-2025

Depends on the OS of the controllers. But I'd say:

Controllers must share the same SSID-related config.
Controllers must be in the same mobility group & mobility domain.

Depends on the firmware version on the controller(s) but they can be different. However, it is best for them to be the same firmware so they can share the same bugs and share the same cause of the crash. There will be some Bug IDs where the Workround recommends not to use Mobility Group because this adds special "tax" to the uncontrollable and untameable WNCD process (9800-40/-80, 9800M, 9800H1/H2).

Mobility Group is fine if the WLC is the 9800-L because there is only one WNCD instance. Any controller with multiple WNCD instance will face issues. That's a guarantee.

eglinsky2012 · ‎07-02-2025

@Leo Laohoo isn’t that mobility group bug you’re referring to specifically for a group that is formed between a 9800 WLC and an AireOS-based WLC? Or do I have that mixed up with something else?

Leo Laohoo · ‎07-02-2025

@eglinsky2012 wrote:

isn’t that mobility group bug you’re referring to specifically for a group that is formed between a 9800 WLC and an AireOS-based WLC? Or do I have that mixed up with something else?

Nope. There are a few (two, if I remembered correctly) that I've read and impacts IOS-XE only.