H3C Technologies H3C S12500 Series Switches - Manual (Page 131)

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Configuring IP forwarding basics
The term "router" in this document refers to both routers and Layer 3 switches.
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
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.
For more information about the routing table, see Layer 3—IP Routing Configuration Guide.
Display brief information about the FIB table by using the display fib command.
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
…
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—LSP index number.