350-401 Question 1

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  From the book: CCNP and CCIE Enterprise Core ENCOR 350-401 Official Cert Guide Forwarding Information Base: The FIB is built directly from the routing table and contains the next-hop IP address for each destination in the network. It keeps a mirror image of the forwarding information contained in the IP routing table. When a routing or topology change occurs in the network, the IP routing table is updated, and these changes are reflected in the FIB. CEF uses the FIB to make IP destination prefix-based switching decisions.

• 1

  A is correct. The Forwarding Information Base (FIB) table - CEF uses a FIB to make IP destination prefix-based switching decisions. The FIB is conceptually similar to a routing table or information base. It maintains a mirror image of the forwarding information contained in the IP routing table. When routing or topology changes occur in the network, the IP routing table is updated, and these changes are reflected in the FIB. The FIB maintains next-hop address information based on the information in the IP routing table. Because there is a one-to-one correlation between FIB entries and routing table entries, the FIB contains all known routes and eliminates the need for route cache maintenance that is associated with switching paths such as fast switching and optimum switching. Adjacency table - Nodes in the network are said to be adjacent if they can reach each other with a single hop across a link layer. In addition to the FIB, CEF uses adjacency tables to append Layer 2 addressing information. The adjacency table maintains Layer 2 next-hop addresses for all FIB entries. Source: https://www.cisco.com/c/en/us/support/docs/routers/12000-series-routers/47321-ciscoef.html