H3C Technologies H3C S7500E Series Switches - Manual (Page 19)

1-2
z Local routing table
z A local routing table stores the routes found by all protocols and delivers the optimal routes to the
FIB table to guide packet forwarding. The selection of an optimal route is based on the
preferences of routing protocols and metrics of routes.
Contents of a routing table
A routing table includes the following key items:
z Destination address: Destination IP address or destination network.
z Network mask: Specifies, in company with the destination address, the address of 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 129.102.8.10
and the mask 255.255.0.0, the address of the destination network is 129.102.0.0. A network mask
is made of a certain number of consecutive 1s. It can be expressed in dotted decimal format or by
the number of the 1s.
z Outbound interface: Specifies the interface through which the IP packets are to be forwarded.
z IP address of the next hop: Specifies the address of the next router on the path. If only the
outbound interface is configured, its address will be the IP address of the next hop.
z Priority for the route. Routes to the same destination but having different nexthops may have
different priorities and be found by various routing protocols or manually configured. The optimal
route is the one with the highest priority (with the smallest metric).
Routes can be divided into two categories by destination:
z Subnet routes: The destination is a subnet.
z Host routes: The destination is a host.
Based on whether the destination is directly connected to a given router, routes can be divided into:
z Direct routes: The destination is directly connected to the router.
z Indirect routes: The destination is not directly connected to the router.
To prevent the routing table from getting too large, you can configure a default route. All packets
without matching any entry in the routing table will be forwarded through the default route.
In Figure 1-1 , the IP address on each cloud represents the address of the network. Router G is
connected to three networks and therefore has three IP addresses for its three physical interfaces. Its
routing table is shown under the network topology.