Port-Tracking is a simple on/off fabric-wide best practice configuration in the Cisco ACI Fabric.
Why would you want to enable this?
Reason 1 – In the event all uplinks from leaf to spine are down from some type of uplink failure, port-tracking will shut down all downlinks for a specified period of time. By default, all ports continue to operate even though the switch loses fabric connectivity. As a result, dual homed servers and routed connections continue to operate and blackhole traffic.
Reason 2 – During code upgrades, after a switch reboots, downlinks ports become operational before switch is re-joined to the fabric, and may incur packet loss. Port-Tracking ensures ports stay down usually until switch is properly recognized by the fabric and then properly enables the downlink ports.
A bug CSCvs10395 has been released for Port-tracking in January 2020 where if a failure of a REST call between the leaf switch and internal leaf switch REST server fails (rare) it will bring down all of the downlinks for the specified period of time. The switch will recover but an outage on all downlinks will be experienced.
Remediation step – disable port-tracking if in affected release or upgrade to 4.2(3j) or later.