This read-only InterfaceIndexOrZero object reports the ifIndex of the interface on which the vPC peer-keepalive message was last received. Administrators use it to confirm keepalive traffic is arriving on the expected interface, useful when validating that a redundant or backup keepalive path is functioning as intended. For example, if keepalive traffic starts arriving over a backup interface instead of the primary, this object would reveal that a failover of the keepalive path has occurred.