This Gauge32 is the identifier of the port-channel bundle that the peer (fabric-interconnect side) port belongs to. It matters on the internal Ethernet link that carries a blade's traffic from the chassis I/O Module up to a Fabric Interconnect over the backplane because it confirms both ends of this link agree on which aggregate bundle they're part of, which they must for the port-channel to actually pass traffic correctly. A mismatch between aggrPortId on this backplane link and peerAggrPortId here would indicate the two ends of this link disagree about bundle membership, a configuration state worth correcting before it causes a black-holed VLAN.