At which layer does Cisco Express Forwarding use adjacency tables to populate addressing information?

Layer 4 (transport layer) deals with port numbers and end-to-end communication, which is not the function of CEF's adjacency tables for forwarding information.

CEF's adjacency table stores Layer 2 rewrite information, such as MAC addresses and egress interface details, which is crucial for encapsulating packets for the next hop. This allows routers to forward packets directly at Layer 2 without per-packet lookups, optimizing forwarding performance.

Layer 1 (physical layer) deals with the physical transmission of bits, not addressing information populated by adjacency tables for packet forwarding.

Layer 3 (network layer) information, like IP addresses, is used by the Forwarding Information Base (FIB) to determine the next hop, but the adjacency table populates the corresponding Layer 2 rewrite information.