When multiple routing protocols offer a route for the same prefix, what part of the router is in charge of deciding which route to make active?

The Routing Table Manager (RTM) is the process within a router's operating system responsible for populating and managing the main routing table, or Routing Information Base (RIB). When different routing sources (such as IS-IS, OSPF, BGP, or static routes) provide paths to the same prefix, the RTM arbitrates between them. It uses administrative distance (called "preference" in Nokia SR OS) and then protocol-specific metrics to select the single best route to become active and be installed into the RIB and subsequently the FIB.

A: The RIB is the database where routes are stored; it is the output of the RTM's decision, not the decision-maker. C: ECMP is a mechanism for using multiple equal-cost paths from a single protocol, not for choosing between different protocols. D: The FIB is a streamlined table for the forwarding plane, containing only the active routes already selected by the RTM.

- Nokia SR OS Router Configuration Guide, Release 21.x, "Route Policies", section on "Routing Table Manager (RTM)". This section details the RTM's role in selecting the best route from multiple protocol sources based on preference values.

- Nokia SR OS Router Configuration Guide, Release 21.x, "IP Routing Overview", section on "Route Preference".