Configuring adjacency table· 1

Overview·· 1

Introduction to adjacency table· 1

Fields 1

Displaying and maintaining adjacency table· 1

Overview

Introduction to adjacency table

An adjacency table stores information about active neighbors, including neighbor network layer address (nexthop), outgoing interface, link layer service type, and link layer address (PVC for ATM; unavailable for PPP).

The concept of neighbor is relevant to network layer. Node B may be an IP neighbor of node A, while node B may not be an IPX neighbor of node A. Also, a neighbor in the active state is in relation to network layer. The adjacency table feature only supports the neighbor concept in relation to IP.

A router can be connected with its neighbors through multiple link layer protocols, such as PPP, ATM and frame relay (FR).

Fields

Some fields in the adjacency table are describes as follows:

·           Routing interface—Outgoing interface in a route entry.

·           Physical interface—Such as serial interface, POS interface, and ATM interface.

·           Logical interface—An abstract interface that does not correspond to any physical entity and is used for adjacency table implementation, for example, Virtual-Ethernet interface and Virtual-Template interface.

·           Service type—Type of service corresponding to the adjacency table, such as PPP and IP over ATM.

·           Action type—Action to take on the packet that matches the entry, forward or drop.

·           Link media type—Related to the link layer protocol used by the outgoing interface. P2P indicates point-to-point, such as the point-to-point protocol (PPP).

·           Link head information (IPv6)—Information of the link layer header corresponding to the IPv6 protocol.

Displaying and maintaining adjacency table