Which Cisco Express Forwarding component(s) contain forwarding information?

4 thoughts on “Which Cisco Express Forwarding component(s) contain forwarding information?”

1. Seems like A is most correct, since if I understand correctly neither the FIB or adjacency table have enough info to forward traffic by themselves.

   Reply

2. One of those questions where you don´t know what is the best answer from Cisco perspective.

   FIB is used for forwarding
   Adjacency table maintains Layer 2 next-hop addresses for all FIB entries.

   So, they work together in order to forward the packet, from that perspective A should be correct
   But, maybe Cisco was really thinking just about FIB, then D.

   On exam, pick one and hope for the best…

   Reply

3. A is correct

   Reply

4. D

   https://www.cisco.com/c/en/us/support/docs/routers/12000-series-routers/47321-ciscoef.html

   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 prepend Layer 2 addressing information. The adjacency table maintains Layer 2 next-hop addresses for all FIB entries.

   Reply