Wireless Access

I have LMS and backup LMS configured for redundancy in my network. However as Aruba does not support stateful client failover, to what extent the VoWLAN services be impacted during stateful AP failover.

Will the failover result in noticeable distruption to ongoing voice application? Please provide in the details for same. 

it can vary from some disruption to the call being disconnected based on your design.  A call continuing with no disruption is not guaranteed.

How many milli seconds will be the disruption in an ideal rf environment of -65 dBm, 25 SNR & interference controlled deployment?

I don't see any documentation which show how long an ap will take to switch over from LMS to backup LMS or vice versa in the even of failover and for what duration the services on hosts are impact.

Could you please provide on these values?

Hi Adnan,

1. In a general LMS/Backup LMS setup, AP will detect a controller to be down if it missed 8 consecutive heartbeats with the controller.

(Bootstrap threshold=8 in AP system profile defined it).

After missing these 8 heartbeats, it will try to switchover to backup LMS.

Depending on whether CPSEC etc is enabled, it will consume some time in bringing up IPSEC (CPSEC enabled), PAPI & GRE tunnels & then start serving the clients.

Note: The bootstrap threshold for RAP's & Mesh AP's is different.

b) If you are using the new HA feature, failover time can be reduced considerably as AP's will create a standby tunnel to the controller defined under backup LMS.

So, if primary controller goes down, it just activates its backup tunnel 

You can make use of inter-controller heartbeats in the HA profile in case of master-local to speed up the process.

The user guide has explanation for the same.

Hi Nitesh,

Thanks for the valuable response. I am using the new HA feature that lets APs create a standby tunnel to the controller defined under backup LMS. The Heartbeat interval is 100ms and the Heartbeat threshold is 5. So does it signifies, 'with default values it will take a total of 500ms for an AP to failover?

Do the clients re-authenticates post AP failover? If yes, how is client re-authentication time evaluated?
(WLC_0001) #show ha group-profile WLC-0001-HA

HA group information "WLC-0001-HA"
----------------------------------
Parameter                     Value
---------                     -----
Preemption                    Enabled
Over-subscription             Disabled
State Synchronization         Enabled
Pre-shared Key                ********
Inter Controller heartbeat    Enabled
Heartbeat Threshold           5
Heartbeat Interval            100
HA group-member IP address    10.20.0.22 dual
HA group-member IP address    10.20.0.21 dual
HA group-member IPv6 address  N/A

Adnan,

The access points can fail over within two seconds, but that is only half of what to consider.  All clients receive a deauth before failover and that can be disruptive to voice, so I would not count on a voice call maintaining through a failover. 

Thanks Joseph.

What I am looking for is the duration for which the services are impacted under all ideal conditions during AP failover.

We are proposing Aruba for a large deployment and the client is specific to have a documentary evidence from vendor to provide in details as to how long the services are impacted during AP failover in Aruba, since Aruba does not have stateful client failover as Cisco does.

Without this detail we are finding it difficult to submit the proposal.