3Com Switch 8800 Configuration Guide Chapter 16 IP Routing Protocol Overview
16-1
Chapter 16 IP Routing Protocol Overview Note:
A router that is referred to in the following or its icon represents a generalized router or
a Switch 8800 running routing protocols. To improve readability, this will not be
described in the other parts of the manual.
For the configuration of VPN instance, refer to the MPLS chapter in this book.
16.1 Introduction to IP Route and Routing Table
16.1.1 IP Route and Route Segment
Routers are implemented for route selection in the Internet. A router works in the
following way: The router selects an appropriate path (through a network) according to
the destination address of the packet it receives and forwards the packet to the next
router. The last router in the path is responsible for submitting the packet to the
destination host.
In Figure 16-1, R stands for a router. A packet sent from Host A to Host C should go
through two routers and the packet is transmitted through two hops. Therefore, when a
node (router) is connected to another node through a network, they are in the same
route segment and are deemed as adjacent in the Internet. That is, the adjacent routers
refer to two routers connected to the same network. The number of route segments
between a router and hosts in the same network counted as zero. In Figure 16-1, the
bold arrows represent these route segments. Which physical links comprise which
route segment is not a concern of a router however.