Exam 350-401 topic 1 question 186 discussion

https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/8-7/High_Availability_DG.html#pgfId-44041 "When the HA pair is set up, by default, the Primary WLC's MAC address is synced as the Mobility MAC address on the Standby WLC" -> Devices in 5520 HA cluster already have the mobility mac. https://www.cisco.com/c/en/us/td/docs/wireless/controller/9800/config-guide/b_wl_16_10_cg/mobility.html "Ensure that you configure the mobility MAC address using the wireless mobility mac-address command for High-Availability to work" -> Mobility MAC needs to be set manually on new Catalyst 9800.

this allows the 9800 WLC to act as a "anchor" for client roaming, allowing clients to maintain their connection as they roam between access points that are controlled by different controllers and that will to remedy the issue

The mobility MAC on the 9800 WLC needs to match the 5520 HA cluster to maintain consistent mobility identity for seamless client roaming, especially during failover scenarios where the standby controller becomes active. This ensures uninterrupted mobility sessions as the controllers in the mobility group are recognized by a consistent MAC address.

The 9800 needs both MACs for each cluster node. The 5520 cluster only needs one MAC for the 9800. The cluster nodes share the config so if one fails the other should still have the MAC for the 9800, but the 9800 may not have the other MAC for the secondary 5520.

Must be B

B CORRECT ANSWER

To me B is correct. You have 2 5k devices with SSO, and a 1 9k device. If cluster and primary works fine, then everything is fine. However when Primary 5k device fails, secondary should take over. Now Secondary with 9k doesnt talk to each other as it should. Ensure that you configure the mobility MAC address using the wireless mobility mac-address command for HighAvailability to work. Therefore you should enable this on the 9k device so it knows about the other devices. Doing it on the cluster with already established SSO wont do anything. Given answer (B) should be the correct one.

A is correct. Things failed after Active 5520 went down and Standby took the Active role

Provided answer is correct "Once the HA pair is formed, the Mobility MAC cannot be changed or edited". https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/8-7/High_Availability_DG.html#pgfId-44041 That means that other mobility group members (in our case the newly added 9800 WLC) would have to make sure they are configured with the appropriate mobility mac of the existing 5520 cluster. There is NO possibility to change the HA MAC without breaking the HA and re-configure it. Seems there was a misconfiguration by the engineer who configured the new 9800 "to test new features".

Correct me please if I am wrong here. The given answer is correct. Why? After stateful switchover, the standby 5520 will be active. As 'rlilewis' has quoted already, "The Primary units MAC should be used as Mobility MAC in the HA setup in order to form a mobility peer with another HA setup or **independent controller**" So, because after the switchover, the configured MAC address of the primary is no more valid, you need to change the MAC address on the 9800 controller to point it to the MAc address of the secondary.

if mobility MAC wasn't already configured on the 9800, roaming wouldn't have worked. We are told it was working. I think the standby 5520 must have been the one that was forgotten to be configured. I would choose A.

It is the roaming service between the new 5520 and the one 9800 not working (dropping). Seems to me that the new controller not forming a mobility peer with 9800 due to the new mac address of the device. that means there was no mac address sync on HA group of 5520. so A

No, A is correct. The question was quite clear that it was working fine until the 5520 failed over to the secondary node in its cluster. Why would configuring a mobility MAC on the standalone 9800 solve anything? High Availability (SSO) Deployment Guide: https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/8-7/High_Availability_DG.html "The Primary units MAC should be used as Mobility MAC in the HA setup in order to form a mobility peer with another HA setup or **independent controller**"

https://www.cisco.com/c/en/us/td/docs/wireless/controller/9800/config-guide/b_wl_16_10_cg/mobility.html "Ensure that you configure the mobility MAC address using the wireless mobility mac-address command for High-Availability to work."