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Routers are used to select the route in the Internet. A router selects a suitable path 
according to the destination host address contained in a received data packet, and 
sends the data packet to the next router. The last router on the path sends the 
data packet to the destination host.

A router processes the path for transmitting a packet through a network as a 
logical route unit, referred to as a hop. For example, in Figure 142, a packet from 
host A to host C passes through 3 networks and 2 routers for a total of 3 hops. It 
shows that when two nodes are connected to each other by a network, they are 
separated by one hop and are neighbors on the Internet. Similarly, two adjacent 
routers are those connected to the same network. So, the hops from a router to 
the local network host total 0. In the diagram, the bold arrows represent the hops. 
The router does not handle data transmission through the physical links in each 
route unit.

Figure 142   Concept of route segment

Networks vary in size, so the actual length of each hop is also different. Therefore, 
for different networks, the route segments can be multiplied by a weight 
coefficient and then used to measure the length of a path.

If a router in the Internet is regarded as a node on the network, and a hop in the 
Internet is regarded as a link, then routing in the Internet is similar to that in a 
simple network. Sometimes it may not be optimal to select the route with the 
fewest hops. For example, a route passing 3 LAN hops might be much faster than 
a route passing 2 WAN hops.

The routing table is essential for a router to transfer data packets. Every router has 
one routing table. The routing value in the routing table shows which physical port 

B

C

A

R

R

 

R oute 

S egm ent

R

R

R