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- Table of Contents
-
- 06-Layer 3 - IP Services Configuration Guide
- 00-Preface
- 01-ARP Configuration
- 02-IP Addressing Configuration
- 03-DHCP Configuration
- 04-DNS Configuration
- 05-NAT Configuration
- 06-IP Forwarding Basics Configuration
- 07-Adjacency Table Configuration
- 08-IP Performance Optimization Configuration
- 09-UDP Helper Configuration
- 10-IPv6 Basics Configuration
- 11-DHCPv6 Configuration
- 12-IPv6 DNS Configuration
- 13-Tunneling Configuration
- 14-GRE Configuration
- Related Documents
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| Title | Size | Download |
|---|---|---|
| 06-IP Forwarding Basics Configuration | 68.54 KB |
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NOTE: The term router in this document refers to both routers and Layer 3 switches. |
IP forwarding overview
Upon receiving a packet, a router uses the destination IP address of the packet to find a match from the forwarding information base (FIB) table, and uses the matching entry to forward the packet.
FIB table
Introduction
A router 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.
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NOTE: For more information about the routing table, see Layer 3—IP Routing Configuration Guide. |
FIB table information
Display the brief information of the FIB table by using the display fib command.
<Sysname> display fib
Destination count: 6 FIB entry count: 6
Flag:
U:Useable G:Gateway H:Host B:Blackhole D:Dynamic S:Static
R:Relay
Destination/Mask Nexthop Flag OutInterface InnerLabel Token
192.168.1.0/24 0.0.0.0 U Vlan999 Null Invalid
192.168.1.40/32 127.0.0.1 UH InLoop0 Null Invalid
…(Part of the output information is omitted)
A FIB entry includes the following items:
· Destination—Destination IP address
· Mask—Network mask. The mask and the destination address identity 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 is made up of 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
· InnerLabel—Inner label
· Token—Label switched path (LSP) index number
Displaying and maintaining the FIB table
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Task |
Command |
Remarks |
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Display FIB information. |
display fib [ multiple-topology topology-name | vpn-instance vpn-instance-name ] [ acl acl-number | ip-prefix ip-prefix-name ] [ | { begin | exclude | include } regular-expression ] |
Available in any view |
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Display FIB information matching the specified destination IP address. |
display fib [ multiple-topology topology-name | vpn-instance vpn-instance-name ] ip-address [ mask | mask-length ] [ | { begin | exclude | include } regular-expression ] |
Available in any view |
