Route recursion
To use a BGP, static, or RIP route that has an indirectly connected next hop, a router must perform route recursion to find the output interface to reach the next hop.
Link-state routing protocols, such as OSPF and IS-IS, do not need route recursion, because they obtain directly connected next hops through route calculation.
The RIB records and saves route recursion information, including brief information about related routes, recursive paths, and recursion depth.