Contents

Basic IP forwarding on the device···································································· 1

FIB table········································································································································· 1

Saving the IP forwarding entries to a file······························································································ 1

Displaying FIB table entries··············································································································· 2

Basic IP forwarding on the device

The device uses the destination IP address of a received packet to find a match from the forwarding information base (FIB) table. It then uses the matching entry to forward the packet.

FIB table

A device selects optimal routes from the routing table, and puts them into the FIB table. Each FIB entry specifies the next hop IP address and output interface for packets destined for a specific subnet or host.

For more information about the routing table, see Layer 3—IP Routing Configuration Guide.

Use the display fib command to display FIB table entries. The following example displays the entire FIB table.

<Sysname> display fib

Destination count: 4 FIB entry count: 4

Flag:

  U:Useable   G:Gateway   H:Host   B:Blackhole   D:Dynamic   S:Static

  R:Relay     F:FRR

Destination/Mask   Nexthop         Flag     OutInterface/Token       Label

10.2.0.0/16        10.2.1.1        U        GE2/0/1                  Null

10.2.1.1/32        127.0.0.1       UH       InLoop0                  Null

127.0.0.0/8        127.0.0.1       U        InLoop0                  Null

127.0.0.1/32       127.0.0.1       UH       InLoop0                  Null

A FIB entry includes the following items:

·     Destination—Destination IP address.

·     Mask—Network mask. The mask and the destination address identify the destination network. A logical AND operation between the destination address and the network mask yields the address of the destination network. For example, if the destination address is 192.168.1.40 and the mask 255.255.255.0, the address of the destination network is 192.168.1.0. A network mask includes a certain number of consecutive 1s. It can be expressed in dotted decimal format or by the number of the 1s.

·     Nexthop—IP address of the next hop.

·     Flag—Route flag.

·     OutInterface—Output interface.

·     Token—MPLS Label Switched Path index number.

·     Label—Inner label.

Saving the IP forwarding entries to a file

This feature automatically creates the file if you specify a nonexistent file. If the file already exists, this feature overwrites the file content.

To automatically save the IP forwarding entries periodically, configure a schedule for the device to automatically run the ip forwarding-table save command. For information about scheduling a task, see Fundamentals Configuration Guide.

To save the IP forwarding entries to a file:

Displaying FIB table entries

Execute display commands in any view.