What is used to pre-populate the adjacency table on Cisco devices that use CEF to process packets?

The adjacency table in Cisco devices that use Cisco Express Forwarding (CEF) is pre-populated using the ARP table.

CEF uses two main components to forward packets:

1. The Forwarding Information Base (FIB), which is conceptually similar to a routing table but contains the information that a router would use to forward an IP packet.
2. The adjacency table, which maintains Layer 2 (L2) next-hop addresses for all FIB entries. This table is populated using the ARP table, which maps IP addresses to the MAC addresses of devices that are directly connected on the network. When CEF is enabled, the router uses ARP to find the L2 address that corresponds to the L3 address in the FIB. When a match is found, CEF adds this L2 address to the adjacency table.

The routing table is used to populate the FIB and not directly for the adjacency table. The DSP (Digital Signal Processor) is used in voice and video processing and is not related to packet forwarding or CEF.