350-401 Question #198: Real Exam Question with Answer & Explanation

Question

How does the RIB differ from the FIB?

Options

• AThe RIB is used to create network topologies and routing tables. The FIB is a list of routes to
• BThe FIB includes many routes a single destination. The RIB is the best route to a single
• CThe RIB includes many routes to the same destination prefix. The FIB contains only the best
• DThe FIB maintains network topologies and routing tables. The RIB is a Iist of routes to particular

Explanation

RIB vs. FIB Explained

Option C is correct because the RIB (Routing Information Base) acts as a master routing table that collects and stores all routes learned from various routing protocols (OSPF, BGP, EIGRP, etc.), meaning multiple routes to the same destination prefix can coexist. The FIB (Forwarding Information Base) is then derived from the RIB, containing only the best (lowest-cost/preferred) route per destination, which is what the router actually uses to make real-time forwarding decisions.

Why the distractors are wrong:

• Option A incorrectly attributes network topology creation to the RIB - that is the role of protocols like OSPF's LSDB, not the RIB itself.
• Option B reverses the definitions entirely - it incorrectly assigns the "many routes" role to the FIB and "best route" to the RIB, which is backwards.
• Option D similarly swaps the roles, incorrectly giving the FIB the job of maintaining topologies and routing tables.

💡 Memory Tip: Think RIB = Raw data (all routes collected), FIB = Final decision (best route forwarded). "R before F" mirrors the process: collect first, then choose.

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