R3303-HP HSR6800 Routers Layer 3 - IP Routing Configuration Guide
1
IP routing basics
IP routing directs the forwarding of IP packets 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 Layer 3—IP
Services Configuration Guide.
Routes can be classified by different criteria, as shown in Table 1.
Table 1 Categories of routes
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.
Static routes are easy to configure and require less system resources. They work well in small and stable
networks. In networks where topology changes might occur frequently, using a dynamic routing protocol
is better.
To view brief information about a routing table, use the display ip routing-table command, as shown in
the following example:
<Sysname> 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 Eth1/1
2.2.2.0/24 Static 60 0 12.2.2.2 Eth1/2
80.1.1.0/24 OSPF 10 2 80.1.1.1 Eth1/3
…(Part of the output information is not shown)
A route entry includes the following key items: