cisco WLC 8540 HA Timer

[CiscoWiFiGuy]

Dear Experts,

I am preparing some Project Documentation for a wireless solution and we are using wlc 8540 in HA mode. For HA , WLC will send keepalive updates on every 100msec to check the Status of Hotstandby unit via RP Port. But in documentation i am required to put exact failover time. So can i assume that on 101th msec , failover will happen? and for that i need to provide some cisco docs in which exact failover timers are mentioned.

can you please guide me on this.?

cheers,

Thanks,

waqas

[Ric Beeching · Accepted solution]

Hi Waqas,

Try this document: High Availability Tech Note

The time it takes for failover in case of power failure on an Active Box also depends on the Keepalive timer configured on the WLC (configured for 100 msec by default). The algorithm it takes to decide the failover is listed here:

• The Standby WLC sends Keepalive to the Active WLC and expects and acknowledgment within 100 msec as per the default timer. This can be configured in range from 100-400 msec.
• If there is no acknowledgment of Keepalive within 100 msec, the Standby WLC immediately sends an ICMP message to the Active WLC via the redundant management interface in order to check if it is a box failover or some issue with Redundant Port connection.
• If there is no response to the ICMP message, the Standby WLC gets aggressive and immediately sends another Keepalive message to the Standby WLC and expects an acknowledgment in 25% less time (that is, 75 msec or 25% less of 100 msec).
• If there is no acknowledgment of Keepalive within 75 msec, the Standby WLC immediately sends another ICMP message to the Active WLC via the redundant management interface.
• Again, if there is no response for the second ICMP message, the Standby WLC gets more aggressive and immediately sends another Keepalive message to the Standby WLC and expects an acknowledgment in time further 25% of actual timer less from last Keepalive timer (that is, 50 msec or last Keepalive timer of 75 msec - 25% less of 100 msec).
• If there is no acknowledgment of the third Keepalive packet within 50 msec, the Standby WLC immediately sends another ICMP message to the Active WLC via the redundant management interface.
• Finally, if there is no response from the third ICMP packet, the Standby WLC declares the Active WLC is dead and assumes the role of the Active WLC.

Network Failover

In the case of a Network Failover (that is, the Active WLC cannot reach its gateway for some reason), it may take 3-4 seconds for a complete switchover depending on the number of APs in the network.

Cheers,

Ric

[CiscoWiFiGuy]

Dear Ric,

Thanks for sharing this valuable info. Surely it will help me to have them in our wireless Deliverables as a reference.

cheers 😉

Thanks,

waqas