04-Layer 3-IP Services Configuration Guide

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05-IP forwarding basics configuration
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05-IP forwarding basics configuration 47.95 KB


Configuring IP forwarding basic settings························································ 1

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

Saving the IP forwarding entries to a file··························································································· 2

Display and maintenance commands for FIB table············································································ 2


Configuring IP forwarding basic settings

About FIB table

A device uses the FIB table to make packet forwarding decisions.

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 the FIB table. The following example displays the entire FIB table.

<Sysname> display fib


Destination count: 8 FIB entry count: 8



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

  R:Relay     F:FRR


Destination/Mask   Nexthop         Flag     OutInterface/Token       Label       UH       InLoop0                  Null       U        InLoop0                  Null       UH       InLoop0                  Null       UH       InLoop0                  Null       UH       InLoop0                  Null         UB       NULL0                    Null         UB       NULL0                    Null       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 and the mask, the address of the destination network is 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

Restrictions and guidelines

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

This feature triggers one-time saving of the IP forwarding entries.

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, execute the following command in any view:

ip forwarding-table save filename filename

Display and maintenance commands for FIB table

Execute display commands in any view.




Display FIB entries.

display fib  [ ip-address [ mask | mask-length ] ]




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