This read-only INTEGER gives the IP interface index of the next-hop router for a given forwarding-table entry, linking a route to the specific local interface used to reach it. Admins rely on this to verify that a destination's traffic is egressing through the interface they expect, especially after topology or routing-table changes. For instance, after adding a new WAN uplink, checking this OID for a remote subnet's entry confirms traffic is now flowing out the new interface rather than the old one.