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			Home &gt; Graph Theory: Networking
					&gt; The Internet
					&gt; Distance-Vector Routing</div>
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        <a class="toc_link" href="page21.xml">Designing A Routing Protocol</a>
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        <a class="toc_link" href="page30.xml">Distance-Vector Routing</a>
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        <a class="toc_link" href="page33.xml">Link-State Routing</a>
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    <div id="content"><h1>Distance-Vector Routing</h1>
				<p>
				Distance-vector routing makes this assumption:
				</p>
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					Each router knows the identity of every other router in the network.
					</p>
					
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				<p>
				In an attempt to enforce this assumption, each router will maintain a
				<i>distance vector</i>, comprised of the list of tuples:
				</p>
				<p>
				<code>&lt; destination, cost &gt;</code>
				</p>
				<p>
				... for all nodes in the network. Here, <code>cost</code> is the
				current <b>estimate</b> of the shortest path from this
				router to the <b>destination</b>; the estimate is never
				smaller than the real cost of the path.
				</p>
				<p>
				The distance-vector algorithm is a distributed implementation of the 
				<a href="bellman_theory.html">
				Bellman-Ford algorithm</a>:
				</p>
				<ol><li>
					Each router periodically sends a copy of its distance vector to its neighbors.
					</li><li>
					When a router receives a distance vector from a neighbor, it determines 
					whether its cost of reaching any destination would decrease if packets 
					to that destination were to be sent through that neighbor.
					</li><li>
					If so, that router updates its own distance vector.
					</li></ol>
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