A quick question.
What happens to roaming when controller goes down?
The APs are in FlexConnect Mode - Local Switching.
My understanding is that the connected clients will be served using local switching, but no new clients will be able to connect.
So, what happens to the roaming for the connected clients? Would they still be able to roam between APs?
Very interesting question. I understand that it depends on the key management algorithm.
For WPA2/PSK with no CCKM clients will perform full authentication again when roaming, so, there will be no roaming for this.
But if a client had a full authentication using RADIUS and the Access Points have the PMK from the last authentication then a client is able to roam even though the WLC is down.
So, the question is if there's a key management in place and AP have PMK available.
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It depends on your deployment.
If the Flex connect Local Auth is enabled then the AP will allow the Wireless clients to roam between the Flex Aps. You can even have Fast Roaming if Flex groups are configured.On Flex connect Local Switching + Central Auth, the roam is possible only for the clients that was authenticated before the WLC went down.
Refer this document, you will get a good idea on Client Roaming on Flex connect deployment: https://www.cisco.com/c/en/us/support/docs/wireless-mobility/wireless-lan-wlan/116493-technote-technology-00.html