This identifies, by its index in the FCIP link table, which specific FCIP link is used to reach a particular remote FC domain that was learned dynamically rather than configured statically. This mapping is what a management tool traverses to answer which physical or logical FCIP link carries traffic to a given remote domain, which matters when troubleshooting reachability to a specific remote fabric domain in a topology with multiple redundant FCIP links. If FC domain 0x05 is reachable via link index 3, an admin diagnosing slow or failed traffic to that domain would go check the health and statistics of specifically that link, not any of the other configured FCIP links.