Symptoms
In BIG-IP software versions 11.2.1, 11.3.0, 11.4.0, 11.4.1, 11.5.0, 11.5.1, 11.5.2, 11.5.3, 11.5.4, 11.6.0, and 12.0.0, the serial failover 'Active' signal is asserted even if the unit is not configured to be in a high availability (HA) pair. A unit can become Standalone if the configuration is reset, or if a return merchandise authorization (RMA) is performed. If the serial cable is still connected to its peer, then the HA peer may defer the Active status to the Standalone system, which does not actually take over and process traffic.
Impact
Traffic is interrupted when the Active unit transitions to Standby.
Conditions
Serial cable failover in-use between two members of an HA pair.
Workaround
During an RMA, the serial cable failover can be temporarily disabled on the Active unit by issuing the following command:
tmsh modify sys db failover.usetty01 value disable
Fix Information
A Standalone unit does not spuriously assert that it is Active if the unit is not configured to be in a high availability (HA) pair when the serial cable is connected during failover. (This is the version 10.x behavior.)
