3Com Switch 7750 Configuration Guide Guide

30
IP ROUTING PROTOCOL OVERVIEW
n
When running a routing protocol, the Ethernet switch also functions as a router.
The word "router" and the router icons covered in the following text represent
routers in common sense and Ethernet switches running a routing protocol. To
improve readability, this will not be mentioned again in this manual.
Introduction to IP
Route and Routing
Table
IP Route and Route
Segment
Routers are used for route selection on the Internet. As a router receives a packet,
it selects an appropriate route (through a network) according to the destination
address of the packet and forwards the packet to the next router. The last router
on the route is responsible for delivering the packet to the destination host.
A route segment is a common physical network interconnecting two nodes, which
are deemed adjacent on the Internet. That is, two routers connected to the same
physical network are adjacent to each other. The number of route segments
between a router and any host on the local network is zero. In the following
figure, the bold arrows represent route segments. A router is not concerned about
which physical links compose a route segment. As shown in
Figure 63, a packet
sent from Host A to Host C travels through two routers over three route segments
(along the broken line).
Figure 63 Route segment
The number of route segments on the path between a source and destination can
be used to measure the "length" of the path. As the sizes of networks may differ
Host A
Host C
Route
Segment
Host B