1-3
e
Figure 1-1
A sample routing tabl
Router A
Router B
Router H
Router E
16.0.0.2
17.0.0.3
15.0.0.0
12.0.0.0
17.0.0.0
11.0.0.0
16.0.0.0
13.0.0.0
14.0.0.0
Router C
Router D
Router F
Router G
11.0.0.1
12.0.0.1
12.0.0.2
15.0.0.1
15.0.0.2
17.0.0.1
16.0.0.1
13.0.0.1
13.0.0.2
14.0.0.1
14.0.0.2
14.0.0.3
14.0.0.4
17.0.0.2
11.0.0.2
13.0.0.3
Destination Network
Nexthop
Interface
11.0.0.0 11.0.0.1 2
12.0.0.0 12.0.0.1 1
13.0.0.0 12.0.0.2 1
14.0.0.0 14.0.0.4 3
15.0.0.0 14.0.0.2 3
16.0.0.0 14.0.0.2 3
17.0.0.0 11.0.0.2 2
Routing Protocol Overview
Static Routing and Dynamic Routing
Static routing is easy to configure and requires less system resources. It works well in small, stable
networks with simple topologies. Its major drawback is that you must perform routing configuration
again whenever the network topology changes; it cannot adjust to network changes by itself.
Dynamic routing is based on dynamic routing protocols, which can detect network topology changes
and recalculate the routes accordingly. Therefore, dynamic routing is suitable for large networks. Its
disadvantages are that it is difficult to configure, and that it not only imposes higher requirements on the
system, but also consumes a certain amount of network resources.
Routing Protocols and Routing Priority
Different routing protocols may find different routes to the same destination. However, not all of those
routes are optimal. In fact, at a particular moment, only one protocol can uniquely determine the current
optimal route to the destination. For the purpose of route selection, each routing protocol (including
static routes) is assigned a priority. The route found by the routing protocol with the highest priority is
preferred.
The following table lists some routing protocols and the default priorities for routes found by them:
