Cisco Express Forwarding (CEF) maintains two tables in the data plane. Specifically, the Forwarding Information Base (FIB) maintains Layer 3 forwarding information, whereas the adjacency table maintains Layer 2 information for next hops listed in the FIB.
Using these tables, populated from a router’s IP routing table and ARP cache, CEF can efficiently make forwarding decisions. Unlike fast switching, CEF does not require the first packet of a data flow to be process switched. Rather, an entire data flow can be forwarded at the data plane, as seen in Figure 11-3