3Com Switch 8800 Configuration Guide Chapter 16 IP Routing Protocol Overview
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Route
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Figure 16-1 The concept of route segment
As the networks may have different sizes, the segment lengths connected between two
different pairs of routers are also different. The number of route segments multiplies a
weighted coefficient can serve as a weighted measurement for the actual length of the
signal transmission path.
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. Message routed through the shortest route
may not always be the optimal route. For example, routing through three high-speed
LAN route segments may be much faster than that through two low-speed WAN route
segments.
16.1.2 Route Selection through the Routing Table The key for a router to forward packets is the routing table. Each router saves a routing
table in its memory, and each entry of this table specifies the physical port of the router
through which the packet is sent to a subnet or a host. Therefore, it can reach the next
router via a particular path or reach a destination host via a directly connected network.
A routing table has the following key entries:
z Destination address: It is used to identify the destination IP address or the
destination network of an IP packet.
z Network mask: Combined with the destination address, it is used to identify the
network address of the destination host or router. If the destination address is
ANDed with the network mask, you will get 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