What is AP behavior when 5500 controller goes down?

[rharland]

Had this question from a client today, and couldn't find the answer readily - so here goes:

When a 5500 goes offline or fails for whatever reason, what happens to the clients connected to the APs managed by said controller?

Do all users lose connectivity immediately, retain until next auth refresh, or some other result?

Thanks for any information!

[blakekrone]

Depends on the AP modes. If the AP is in local mode once the controller goes down all APs are down and clients are disconnected.

If the APs are in HREAP mode then they will stay online and currently connected clients will stay connected, depending on the authentication used new clients may or may not be connected.

[daviwatk]

Hi Russ,

This could really become a multi-part question as it depends on the "mode" of the AP, and the security method in place (for FlexConnect).

So, for the sake of simplicity, assuming these are "Local Mode" APs

1. If the "WLC" goes down; powers off; blows up; or otherwise becomes unreachable by the AP, clients would "immediately" stop passing traffic.  Now, they would "pass" traffic to the AP, who will try to forward upstream via the CAPWAP tunnel; however it wouldn't make it anywhere.

2. The APs will be generating DTLS keep-alives (hearbeat) with a default of every 30 seconds towards the WLC.  If the hearbeat is not responded to, the AP will re-transmit, until it reaches it's maximum retries for the DTLS heartbeat.  At this point in time the AP will force a close of the DTLS connection and fall back to discovery, where-by it will follow the usual presedence for discovery/join.

So, as far as what happens to the "client".  If the WLC went down, client's would not be getting anything done as soon as that happened.  Now, the clients may still "think" they are connected; and it will not be until the AP tears down the DTLS connection for the client to not be associated to the AP, nor see any WLANs.

[daviwatk]

Beat me to it

Essentially, if you are using H-REAP, there are several "scenarios" that may result in different behavior, so that kind of depends upon the configuration.

Bottom line, if you're in local mode and the WLC goes down, your client is done (AP failover aside).