Behaviour of N+1

[s.hellman]

We have four WLC 5508 and four WLC 5520. One 5508 and one 5520 is configured as backup controllers (N+1) (http://www.cisco.com/c/en/us/td/docs/wireless/technology/hi_avail/N1_High_Availability_Deployment_Guide.pdf).

Controller 5508-1 ,-2 and -3 have 5508-4 configured as backup controller.

Controller 5520-1 ,-2 and -3 have 5520-0 configured as backup controller.

But today when we did an upgrade of 5508-1 and the controller restarted, all AP on that controller moved to 5520-0, not to 5508-4 as configured.

Why did this happen?

[M. Wisely]

Have you configured a secondary controller on the AP to point to 5508-4?

[s.hellman]

No, according to the deployment guide that does not seem to be necessary.

If you had to, there should be no point to point out the backup controller on the other controllers.

[Rasika Nayanajith]

It seems AP knew about 5520-1 & failover to it. 

Do they (5508-1 & 5520-1) belong to same mobility group ? Do they have same subnet IPs ?

Here is the AP failover process when you have configured that feature

http://www.cisco.com/c/en/us/td/docs/wireless/controller/8-0/configuration-guide/b_cg80/b_cg80_chapter_01101111.html#ID2960

HTH

Rasika

[s.hellman]

From the guide that you posted a link to:

"If the access point’s local controller fails, it chooses an available controller from the backup controller list in this order: primary, secondary, tertiary, primary backup, and secondary backup."

We only have configured a primary controller on the AP and a primary backup controller globally on each controller. So when the AP looses connection with its primary controller it should choose the primary backup controller.

But it is a bit confusing, from the guide that we have followed, http://www.cisco.com/c/en/us/td/docs/wireless/technology/hi_avail/N1_High_Availability_Deployment_Guide.pdf it says that the AP will reboot after loosing connection with its primary controller and when it starts it will choose the backup controller. But the guide that you are linking to, it does not mention any reboot. Has this changed in newer version of firmware? We are running 8.0 on the 5508's and 8.2 on the 5520's.

If the AP is rebooting, when will it get the info of the backup controller? Will it get the info during start up from the first controller responding? That could explain the behaviour if a 5520 controller responds first, and the AP joins the 5520 backup controller. If the AP remains the list during reboot, it should try to join the 55008 backup controller.