Have you looked at this guide.... there are some differences in confiugration, but in VSS there is more of a timeout
Client SSO (Client Stateful Switchover)
To support High Availability without impacting the service, there needs to be support for seamless transition of the clients and APs from the active controller to the standby controller. Release 7.5 supports Client Stateful Switch Over (Client SSO) in Wireless LAN controllers. Client SSO will be supported for clients, which have already completed the authentication and DHCP phase and have started passing traffic. With Client SSO, the client’s information is synced to the Standby WLC when client associates or the client parameters change. Fully authenticated clients, i.e. ones in Run state, are synced to the Standby and thus, client re-association is avoided on switchover making the failover seamless for the AP as well as for the client.
Client SSO will work with Anchor-Foreign mobility setup as well as Guest Anchor scenarios.
L3 MGIDs are synced to the Standby Controller.
The failover time varies from ~2-996 milliseconds depending on the category of box failover.
The management gateway failover time is in the order of ~15 seconds, which is the time taken for 12 pings to the management gateway.
The default RTT latency between the two WLCs is 80 milliseconds. RTT latency should be less than or equal to 80% of the Keepalive timer. The Keepalive timer is configurable in the range 100-400 milliseconds
i have followed the HA instructions for VSS , but according to the guide :
-failover time from 2-996 msec .
- the highlighted "it taks 15 seconds" in case of gateway unreachbalilty . however , in my test that matches what cisco did for the failover , i did force-switchover ....., so why i got high traffic interrupt unlike what cisco got 0% loss.
also when i repeated the test , the client disconnects for short while (like 2-3 seconds ) then reconnect back again . but total traffic interruption time is around 5-6 missed pings
Transferring Crash file from standby: Login to the Active WLC in HA.
From CLI: (Cisco Controller) >transfer upload datatype crash (Cisco
Controller) >transfer upload filename (Cisco
Controller) >transfer upload mode tftp (Cisco Controller) >transfer
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