R3303-HP HSR6800 Routers Layer 3 - IP Services Configuration Guide

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Configuring adjacency table
The adjacency table feature only applies to hardware forwarding, but not software forwarding.
The adjacency table feature does not apply to Ethernet networks that use ARP for storing and managing
neighbor information.
Overview
An adjacency table stores information about active neighbors, including neighbor network layer address
(nexthop), output 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, but not 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 device can be connected with its neighbors through multiple link layer protocols, such as PPP, ATM,
and frame relay (FR).
The products supporting hardware forwarding can apply the adjacency table to the drivers to implement
hardware forwarding. In hardware forwarding, the link layer header of the packet to be forwarded is
quickly filled according to the adjacency table, and then the packet is forwarded through the output
interface.
Adjacency table fields
Fields in the adjacency table are described as follows:
• Routing interface—Output 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 output interface. P2P indicates
point-to-point, such as PPP.
• Link head information (IPv6)—Information about the link layer header corresponding to the IPv6
protocol.
Displaying and maintaining adjacency table