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

The adjacency table on Cisco devices that utilize Cisco Express Forwarding (CEF) is primarily pre-populated using entries from the Address Resolution Protocol (ARP) table. CEF is a highly efficient packet forwarding mechanism that improves routing performance by maintaining an adjacency table, which includes information about the next-hop addresses and their associated outbound interfaces.

When a device needs to forward a packet, it checks the adjacency table to find out the appropriate next-hop information. The ARP table contains mappings of IP addresses to MAC addresses, which allows CEF to resolve the layer 2 destination address needed to forward packets towards the next hop.

In this context, while the routing table provides necessary information regarding how to reach different networks, it does not directly contribute to the entries within the adjacency table. The Routing Information Base (RIB) relates to how routing protocols maintain routing data but does not populate the adjacency table either. The neighbor table is more commonly associated with Layer 2 protocols, such as Neighbor Discovery Protocol (NDP) on IPv6 or CDP on Cisco devices, rather than with CEF directly, which emphasizes the use of the ARP table for resolving MAC addresses after determining the correct next hop from the routing information.

Thus, the significance of the AR