3Com 10014298 manual About Hops

82CHAPTER 5: IP ROUTING PROTOCOL OPERATION

Figure 22 About Hops

A R R

Route

Segment

R

R

R

C

B

Networks can have different sizes, so, the segment lengths connected between two different pairs of routers are also different.

If a router in a network is regarded as a node and a route segment in the Internet is regarded as a link, message routing in the Internet works in a similar way as the message routing in a conventional network. Routing a message through the shortest route may not always be the optimal route. For example, routing through three LAN route segments may be much faster than a route through two WAN route segments.

Configuring the IP Routing Protocol Overview is described in the following sections:

■Selecting Routes Through the Routing Table

■Routing Management Policy

Selecting Routes For the router, a routing table is the key to forwarding packets. Each router saves a Through the Routing routing table in its memory, and each entry in this table specifies the physical port Table of the router through which a packet is sent to a subnet or a host. The packet can reach the next router over a particular path or reach a destination host through a

directly connected network.

A routing table has the following key entries:

■A destination address — Identifies the destination IP address or the destination network of the IP packet, which is 32 bits in length.

■A network mask — Is made up of several consecutive 1s, which can be expressed either in the dotted decimal format, or by the number of the consecutive 1s in the mask. Combined with the destination address, the network mask identifies the network address of the destination host or router. With the destination address and the network mask, you have the address of the network segment where the destination host or router is located. For example, if the destination address is 129.102.8.10, the address of the network where the host or the router with the mask 255.255.0.0 is located is 129.102.0.0.