This notification-carried object reports the ifIndex of the interface most relevant to a session-down event, falling back to the interface associated with one of the affected neighbors if no interface can be directly correlated. Admins use it in the jnxLdpSesDown trap to immediately know which local interface to investigate, without having to cross-reference the failed peer against the interface table separately. A trap carrying jnxLdpSesDownIf of 78 tells the admin that interface's ifIndex is the one associated with the failed LDP session, a good starting point for the investigation.