Configuring adjacency table· 1

Adjacency table· 1

Displaying the adjacency table· 2

The adjacency table stores information about directly connected neighbors for IP forwarding. The command output only displays adjacency entries for Tunnel interfaces. For information about Tunnel interfaces, see Layer 3—IP Services Configuration Guide.

The neighbor information is generated, updated, and deleted by link layer protocols (such as PPP or ATM) through negotiation (such as PPP dynamic negotiation) or configuration (such as ATM static configuration). An adjacency entry contains the neighbor network layer address (next hop), output interface, link layer protocol type, and link layer address (PVC for ATM, unavailable for PPP).

During IP forwarding, a device checks the FIB to find the output interface and next hop, uses the output interface and next hop address to obtain the link layer forwarding information including the link layer protocol (such as PPP or HDLC), the media type (P2P or NBMA), and the link layer header information in the adjacency table, and encapsulates and forwards the packet.

Adjacency table

Use the display adjacent-table command to display adjacency table entries. For example, display detailed information about all IPv4 adjacency entries.

<Sysname> display adjacent-table all verbose

 IP Address                  : 0.0.0.0

 Routing Interface           : Tunnel3

 Physical Interface          : Tunnel3

 Logical Interface           : N/A

 Service Type                : TUNNEL

 Action Type                 : FORWARDING

 Link Media Type             : P2P

 Slot                        : 1

 Virtual Circuit Information : N/A

 Link Head Information(IP)   : ff030021

 Link Head Information(MPLS) : ff030281

An adjacency entry mainly contains the following items:

·           IP address—IP address of the next hop in FIB table for packet forwarding. This address is used for adjacency table look up.

·           Routing interface—Output interface in the matching route entry. This interface may be logical or physical.

·           Physical interface—Output physical interface that sends matching packets. If the routing interface is a physical one, the routing interface and physical interface are the same. If the routing interface is a logical one, the routing interface and physical interface are different.

·           Logical interface—Logical interface for sending packets, such as a VLAN interface or an aggregate interface.

·           Service type—Link layer protocol type, such as PPP or HDLC.

·           Action type—Action to be taken on the matching packet, forward or drop.

·           Link media type—Related to the link layer protocol used by the routing interface. P2P indicates a point-to-point link and NBMA indicates a non-broadcast muti-access link.

·           Link head information (IP)—Link layer header for IP forwarding.

·           Link head information (MPLS)—Link layer header for MPLS forwarding.

Displaying the adjacency table 

Execute display commands in any view.