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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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Chapter 5. Routing protocols<br />

5<br />

This chapter provides an overview of <strong>IP</strong> routing <strong>and</strong> discusses the various<br />

routing protocols used.<br />

One of the basic functions provided by the <strong>IP</strong> protocol is the ability to form<br />

connections between different physical networks. A system that performs this<br />

function is called an <strong>IP</strong> router. This type of device attaches to two or more<br />

physical networks <strong>and</strong> forwards datagrams between the networks.<br />

When sending data to a remote destination, a host passes datagrams to a local<br />

router. The router forwards the datagrams toward the final destination. They<br />

travel from one router to another until they reach a router connected to the<br />

destination’s LAN segment. Each router along the end-to-end path selects the<br />

next hop device used to reach the destination. The next hop represents the next<br />

device along the path to reach the destination. It is located on a physical network<br />

connected to this intermediate system. Because this physical network differs<br />

from the one on which the system originally received the datagram, the<br />

intermediate host has forwarded (that is, routed) the <strong>IP</strong> datagram from one<br />

physical network to another.<br />

© Copyright <strong>IBM</strong> Corp. 1989-2006. All rights reserved. 171

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