3com 3031 Instruccion De Instalación

Routers are adopted for route selection on the Internet. According to the 
destination address of a received packet, a router selects an appropriate route (via 
a network) and forwards the packet to the next router. The last router is 
responsible for forwarding the packet to the destination host.

For example, in Figure 121, from host A to host C, there are totally 3 networks, 2 
routers. If a node is connected to another node through a network, there will be a 
route segment between these two nodes. They are thus deemed as adjacent in the 
Internet. Similarly, adjacent routers refer to two routers connected to the same 
network. The number of route segments between a router and certain host in the 
same network is taken as zero. In the following figure, the bold arrows represent 
these route segments. A router does not concern about which physical links 
constitute this route segment.

Figure 121   Route segment

As the sizes of the networks may differ greatly, the actual "length" of the router 
segments may be different from each other. Therefore, for different networks, the 
number of route segments multiplies a weighted coefficient can measure the 
actual length of the path.

If a router in a network is regarded as a node in the network and a route segment 
in the Internet is regarded as a link in the Internet, routing in the Internet is similar 
to routing in a simple network. Routing through the shortest route is not always 

Host A

Host C

Route Segment

Host B