This carries the IP address of the specific node along the LSP where an AIS (Alarm Indication Signal) fault was detected, pinpointing where in a potentially multi-hop tunnel the problem originates rather than just flagging the tunnel as a whole. An admin uses this address to jump directly to the offending midpoint router instead of walking the entire LSP path hop by hop during an outage. For example, a faulted-node address of 10.40.2.1 tells the admin to start troubleshooting at that specific core router rather than at the head-end or tail-end.