Cisco CCNA Exam: Fast Packet Forwarding Feature

Fast Packet Forwarding Feature

Prev Question Next Question


Which feature builds a FIB and an adjacency table to expedite packet forwarding?



Click on the arrows to vote for the correct answer

A. B. C. D.


The correct answer is D. Cisco Express Forwarding (CEF).

Cisco Express Forwarding (CEF) is a high-performance Layer 3 switching technology used to forward packets in a network. CEF builds two tables to expedite packet forwarding: the Forwarding Information Base (FIB) and the adjacency table.

The FIB contains a list of all routes known to the router, including the next hop information for each route. The FIB is used to make forwarding decisions for packets.

The adjacency table contains Layer 2 (data link) addressing information for next-hop devices. The adjacency table is used to quickly determine the destination MAC address for packets that need to be forwarded.

Together, the FIB and adjacency tables allow CEF to perform packet forwarding at very high speeds. When a packet arrives at a router, CEF uses the FIB to determine the best path to forward the packet and the adjacency table to determine the destination MAC address. This allows the packet to be forwarded without additional processing, which improves network performance.

Option A, cut through, is a switching method that forwards frames as soon as the destination address is known, without waiting for the entire frame to be received. Cut-through switching can reduce latency but may forward damaged frames, which can lead to network errors.

Option B, fast switching, is a switching method that caches the next-hop information for a packet and uses that information for subsequent packets. Fast switching can improve performance compared to process switching, but not as much as CEF.

Option C, process switching, is a switching method that uses the CPU to process each packet as it arrives. Process switching can be very slow and is not recommended for high-speed networks.