The port tracking feature manages the status of downlink ports on each leaf node based on the status of its fabric ports. Fabric ports are the links between leaf and spine nodes. Links between tier-1 and tier-2 leaf nodes in multi-tier topologies and links between remote leaf nodes (back-to-back links) are also considered to be fabric links.

When this feature is enabled and the number of operational fabric ports on a given leaf node is decreased to the configured threshold or lower, the downlink ports of the leaf node will be brought down so that external devices can switch over to other healthy leaf nodes. When the number of operational fabric ports comes back up to greater than the configured threshold, the downlink ports will be brought back up. At this time, there will be a wait time of the configured delay before the downlink ports are brought up. If the leaf node is part of a vPC peer and does not have any infra ISIS adjacencies--meaning that the node is unable to communicate with the other vPC peer leaf node--when port tracking is triggered such as when all fabric ports went down, the wait time for the vPC downlink ports to come up after the status restoration will be the longer time of either the vPC delay timer or the configured delay in port tracking. Non-vPC downlink ports always follow the delay timer configured in port tracking.

Beginning in Cisco Application Centric Infrastructure (ACI) switch release 14.2(1), the status of fabric infra ISIS adjacency (represented by the attribute aggFabAdjOperSt of the managed object class isisDom) is also checked as an alternative condition to trigger the shutdown of downlink ports. The check is performed to cover a scenario in which fabric ports on a given leaf node are up, but the leaf node has lost reachability to other Cisco ACI nodes for another reason. This condition is always checked when the feature is enabled regardless of the other parameters, such as the minimum number of operational fabric ports. However, it is not applicable to remote leaf nodes because those nodes do not rely on ISIS for fabric infra reachability.

Beginning in Cisco ACI switch release 15.0(1), the "Include APIC ports" option is supported. This option is disabled by default. When this option is disabled, port tracking only brings down downlink ports that are configured for user traffic (that is, ports that are in use by EPGs or L3Outs) while downlink ports connected to the Cisco Application Policy Infrastructure Controllers (APICs) or unused ports are not brought down. When this option is enabled, port tracking brings down all downlink ports on the leaf node. Prior to release 15.0(1), downlink ports that were configured for user traffic were brought down while ports connected to the Cisco APIC were not, and you could not configure port tracking to bring down ports that were connected to the Cisco APIC.

Note	Port tracking checks the conditions to bring down the ports or bring up the ports every second on each leaf node. FEX fabric ports--that is, the network interface (NIF) to connect the FEX and the FEX's parent leaf node--are not impacted by port tracking.