Which statement about Cisco Express Forwarding is true?

Question

Options

• AIt uses a fast cache that is maintained in a router data plane.
• BIt maintains two tables in the data plane the FIB and adjacency table.
• CIt makes forwarding decisions by a process that is scheduled through the IOS scheduler.
• DThe CPU of a router becomes directly involved with packet-switching decisions.

• A
  2% (1)
• B
  91% (39)
• C
  5% (2)
• D
  2% (1)

Explanation

Cisco Express Forwarding (CEF) Explained

CEF maintains two key tables in the data plane: the Forwarding Information Base (FIB), which is a pre-built routing lookup table derived from the routing table, and the Adjacency Table, which stores Layer 2 next-hop information (MAC addresses). Together, these tables allow line-rate packet forwarding without CPU intervention, making B correct.

Why the distractors are wrong:

• A is incorrect because CEF does not use a "fast cache" - that describes fast switching, CEF's predecessor. CEF uses a pre-populated FIB, not a cache built from prior packet flows.
• C is incorrect because CEF forwarding decisions are made in the data plane hardware, not scheduled through the IOS scheduler - that describes process switching, the slowest method.
• D is incorrect because CEF is specifically designed to remove the CPU from packet-switching decisions, offloading the work to ASICs or the data plane.

Memory Tip: Think of CEF as "Two Tables, No CPU" - the FIB (where to send it) + Adjacency Table (how to address it at Layer 2) = fast forwarding without bothering the processor.

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