H3C Technologies H3C S12500 Series Switches - Manual (Page 17)

1
IP routing basics
IP routing directs IP packet forwarding on routers based on a routing table. This book focuses on unicast
routing protocols. For more information about multicast routing protocols, see IP Multicast Configuration
Guide.
Routing table
A router maintains at least two routing tables: one global routing table and one forwarding information
base (FIB). The FIB table contains only the optimal routes, and the global routing table contains all routes.
The router uses the FIB table to forward packets. For more information about the FIB table, see the Layer
3—IP Services Configuration Guide.
Table 1 categorizes routes by different criteria.
Table 1 Route categories
Criterion Categories
Destination
• Network route—Destination is a network. The subnet mask is less than 32 bits.
• Host route—Destination is a host. The subnet mask is 32 bits.
Whether the
destination is directly
connected
• Direct route—Destination is directly connected.
• Indirect route—Destination is indirectly connected.
Origin
• Direct route—A direct route is discovered by the data link protocol on an interface,
and is also called an "interface route."
• Static route—A static route is manually configured by an administrator.
• Dynamic route—A dynamic route is dynamically discovered by a routing protocol.
To view brief information about a routing table, use the display ip routing-table command:
display ip routing-table
Routing Tables: Public
Destinations : 7 Routes : 7
Destination/Mask Proto Pre Cost NextHop Interface
1.1.1.0/24 Direct 0 0 1.1.1.1 GE3/0/1
2.2.2.0/24 Static 60 0 12.2.2.2 GE3/0/2
80.1.1.0/24 OSPF 10 2 80.1.1.1 GE3/0/3
…
A route entry includes the following key items:
• Destination—IP address of the destination host or network
• Mask—Mask length of the IP address.
• Pre—Preference of the route. Among routes to the same destination, the one with the highest
preference is optimal.