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class="noprint"></div> <div id="content" class="mw-body" role="main"> <a id="top"></a> <div id="siteNotice"></div> <div class="mw-indicators"> </div> <h1 id="firstHeading" class="firstHeading" lang="en">Routing</h1> <div id="bodyContent" class="mw-body-content"> <div id="siteSub">From Wikipedia, the free encyclopedia</div> <div id="contentSub"></div> <div id="jump-to-nav" class="mw-jump"> Jump to: <a href="#mw-head">navigation</a>, <a href="#p-search">search</a> </div> <div id="mw-content-text" lang="en" dir="ltr" class="mw-content-ltr"><div class="hatnote">This article is about routing in networks. For other uses, see <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Routing_(disambiguation)" title="Routing (disambiguation)" class="mw-disambig">Routing (disambiguation)</a>.</div> <div class="hatnote boilerplate seealso">See also: <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Router_(computing)" title="Router (computing)">Router (computing)</a></div> <p><b>Routing</b> is the process of selecting best paths in a network. In the past, the term routing was also used to mean forwarding network traffic among networks. However this latter function is much better described as simply <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Packet_forwarding" title="Packet forwarding">forwarding</a>. Routing is performed for many kinds of networks, including the <a href="/web/20150318213050/http://en.wikipedia.org/wiki/PSTN" title="PSTN" class="mw-redirect">telephone network</a> (<a href="/web/20150318213050/http://en.wikipedia.org/wiki/Circuit_switching" title="Circuit switching">circuit switching</a>), <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Computer_network" title="Computer network">electronic data networks</a> (such as the <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Internet" title="Internet">Internet</a>), and <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Transport_network" title="Transport network">transportation networks</a>. This article is concerned primarily with routing in electronic data networks using <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Packet_switching" title="Packet switching">packet switching</a> technology.</p> <p>In packet switching networks, routing directs <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Packet_forwarding" title="Packet forwarding">packet forwarding</a> (the transit of logically addressed <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Network_packet" title="Network packet">network packets</a> from their source toward their ultimate destination) through intermediate <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Node_(networking)" title="Node (networking)">nodes</a>. Intermediate nodes are typically network hardware devices such as <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Router_(computing)" title="Router (computing)">routers</a>, <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Bridging_(networking)" title="Bridging (networking)">bridges</a>, <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Gateway_(telecommunications)" title="Gateway (telecommunications)">gateways</a>, <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Firewall_(computing)" title="Firewall (computing)">firewalls</a>, or <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Network_switch" title="Network switch">switches</a>. General-purpose <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Computer" title="Computer">computers</a> can also forward packets and perform routing, though they are not specialized hardware and may suffer from limited performance. The routing process usually directs forwarding on the basis of <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Routing_table" title="Routing table">routing tables</a> which maintain a record of the routes to various network destinations. Thus, constructing routing tables, which are held in the router's <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Computer_storage" title="Computer storage" class="mw-redirect">memory</a>, is very important for efficient routing. Most routing algorithms use only one network path at a time. <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Multipath_routing" title="Multipath routing">Multipath routing</a> techniques enable the use of multiple alternative paths.</p> <p>In case of overlapping/equal routes, the following elements are considered in order to decide which routes get installed into the routing table (sorted by priority):</p> <ol> <li><i>Prefix-Length</i>: where longer subnet masks are preferred (independent of whether it is within a routing protocol or over different routing protocol)</li> <li><i>Metric</i>: where a lower metric/cost is preferred (only valid within one and the same routing protocol)</li> <li><i><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Administrative_distance" title="Administrative distance">Administrative distance</a></i>: where a route learned from a more reliable routing protocol is preferred (only valid between different routing protocols)</li> </ol> <p>Routing, in a more narrow sense of the term, is often contrasted with <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Bridging_(networking)" title="Bridging (networking)">bridging</a> in its assumption that <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Network_address" title="Network address">network addresses</a> are structured and that similar addresses imply proximity within the network. Structured addresses allow a single routing table entry to represent the route to a group of devices. In large networks, structured addressing (routing, in the narrow sense) outperforms unstructured addressing (bridging). Routing has become the dominant form of addressing on the Internet. Bridging is still widely used within localized environments.</p> <p></p> <div id="toc" class="toc"> <div id="toctitle"> <h2>Contents</h2> </div> <ul> <li class="toclevel-1 tocsection-1"><a href="#Delivery_semantics"><span class="tocnumber">1</span> <span class="toctext">Delivery semantics</span></a></li> <li class="toclevel-1 tocsection-2"><a href="#Topology_distribution"><span class="tocnumber">2</span> <span class="toctext">Topology distribution</span></a> <ul> <li class="toclevel-2 tocsection-3"><a href="#Distance_vector_algorithms"><span class="tocnumber">2.1</span> <span class="toctext">Distance vector algorithms</span></a></li> <li class="toclevel-2 tocsection-4"><a href="#Link-state_algorithms"><span class="tocnumber">2.2</span> <span class="toctext">Link-state algorithms</span></a></li> <li class="toclevel-2 tocsection-5"><a href="#Optimised_Link_State_Routing_algorithm"><span class="tocnumber">2.3</span> <span class="toctext">Optimised Link State Routing algorithm</span></a></li> <li class="toclevel-2 tocsection-6"><a href="#Path_vector_protocol"><span class="tocnumber">2.4</span> <span class="toctext">Path vector protocol</span></a></li> </ul> </li> <li class="toclevel-1 tocsection-7"><a href="#Path_selection"><span class="tocnumber">3</span> <span class="toctext">Path selection</span></a></li> <li class="toclevel-1 tocsection-8"><a href="#Multiple_agents"><span class="tocnumber">4</span> <span class="toctext">Multiple agents</span></a></li> <li class="toclevel-1 tocsection-9"><a href="#Route_analytics"><span class="tocnumber">5</span> <span class="toctext">Route analytics</span></a></li> <li class="toclevel-1 tocsection-10"><a href="#See_also"><span class="tocnumber">6</span> <span class="toctext">See also</span></a> <ul> <li class="toclevel-2 tocsection-11"><a href="#Routing_algorithms_and_techniques"><span class="tocnumber">6.1</span> <span class="toctext">Routing algorithms and techniques</span></a></li> <li class="toclevel-2 tocsection-12"><a href="#Routing_in_specific_networks"><span class="tocnumber">6.2</span> <span class="toctext">Routing in specific networks</span></a></li> <li class="toclevel-2 tocsection-13"><a href="#Routing_protocols"><span class="tocnumber">6.3</span> <span class="toctext">Routing protocols</span></a></li> <li class="toclevel-2 tocsection-14"><a href="#Alternative_methods_for_network_data_flow"><span class="tocnumber">6.4</span> <span class="toctext">Alternative methods for network data flow</span></a></li> <li class="toclevel-2 tocsection-15"><a href="#Router_software_and_suites"><span class="tocnumber">6.5</span> <span class="toctext">Router software and suites</span></a></li> <li class="toclevel-2 tocsection-16"><a href="#Router_platforms"><span class="tocnumber">6.6</span> <span class="toctext">Router platforms</span></a></li> </ul> </li> <li class="toclevel-1 tocsection-17"><a href="#References"><span class="tocnumber">7</span> <span class="toctext">References</span></a></li> <li class="toclevel-1 tocsection-18"><a href="#External_links"><span class="tocnumber">8</span> <span class="toctext">External links</span></a></li> </ul> </div> <p></p> <h2><span class="mw-headline" id="Delivery_semantics">Delivery semantics</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=1" title="Edit section: Delivery semantics">edit</a><span class="mw-editsection-bracket">]</span></span></h2> <table style="float:right; clear:both; margin:1em; padding:0; border: thin solid #000; text-align:center;"> <tr> <th style="background-color:#ddd; color:#00F12;"> <p><strong class="selflink">Routing</strong> schemes</p> <p><a href="/web/20150318213050/http://en.wikipedia.org/wiki/File:Cast.svg" class="image"><img alt="Cast.svg" src="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/c/cf/Cast.svg/100px-Cast.svg.png" width="100" height="67" srcset="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/c/cf/Cast.svg/150px-Cast.svg.png 1.5x, //web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/c/cf/Cast.svg/200px-Cast.svg.png 2x" data-file-width="1125" data-file-height="750"/></a></p> </th> </tr> <tr> <th style="border-bottom: thin solid #999;"> <p><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Anycast" title="Anycast">anycast</a></p> <p><a href="/web/20150318213050/http://en.wikipedia.org/wiki/File:Anycast.svg" class="image"><img alt="Anycast.svg" src="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/4/43/Anycast.svg/100px-Anycast.svg.png" width="100" height="67" srcset="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/4/43/Anycast.svg/150px-Anycast.svg.png 1.5x, //web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/4/43/Anycast.svg/200px-Anycast.svg.png 2x" data-file-width="1125" data-file-height="750"/></a></p> </th> </tr> <tr> <th style="border-bottom: thin solid #999;"> <p><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Broadcasting_(networking)" title="Broadcasting (networking)">broadcast</a></p> <p><a href="/web/20150318213050/http://en.wikipedia.org/wiki/File:Broadcast.svg" class="image"><img alt="Broadcast.svg" src="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/d/dc/Broadcast.svg/100px-Broadcast.svg.png" width="100" height="67" srcset="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/d/dc/Broadcast.svg/150px-Broadcast.svg.png 1.5x, //web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/d/dc/Broadcast.svg/200px-Broadcast.svg.png 2x" data-file-width="1125" data-file-height="750"/></a></p> </th> </tr> <tr> <th style="border-bottom: thin solid #999;"> <p><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Multicast" title="Multicast">multicast</a></p> <p><a href="/web/20150318213050/http://en.wikipedia.org/wiki/File:Multicast.svg" class="image"><img alt="Multicast.svg" src="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/3/30/Multicast.svg/100px-Multicast.svg.png" width="100" height="67" srcset="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/3/30/Multicast.svg/150px-Multicast.svg.png 1.5x, //web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/3/30/Multicast.svg/200px-Multicast.svg.png 2x" data-file-width="1125" data-file-height="750"/></a></p> </th> </tr> <tr> <th style="border-bottom: thin solid #999;"> <p><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Unicast" title="Unicast">unicast</a></p> <p><a href="/web/20150318213050/http://en.wikipedia.org/wiki/File:Unicast.svg" class="image"><img alt="Unicast.svg" src="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/7/75/Unicast.svg/100px-Unicast.svg.png" width="100" height="67" srcset="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/7/75/Unicast.svg/150px-Unicast.svg.png 1.5x, //web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/7/75/Unicast.svg/200px-Unicast.svg.png 2x" data-file-width="1125" data-file-height="750"/></a></p> </th> </tr> <tr> <th style="border-bottom: 0 solid #999;"> <p><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Geocast" title="Geocast">geocast</a></p> <p><a href="/web/20150318213050/http://en.wikipedia.org/wiki/File:Geocast.svg" class="image"><img alt="Geocast.svg" src="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/6/6a/Geocast.svg/100px-Geocast.svg.png" width="100" height="67" srcset="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/6/6a/Geocast.svg/150px-Geocast.svg.png 1.5x, //web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/6/6a/Geocast.svg/200px-Geocast.svg.png 2x" data-file-width="1125" data-file-height="750"/></a></p> </th> </tr> <tr> <td> <div class="plainlinks hlist navbar mini" style=""> <ul> <li class="nv-view"><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Template:Routing_scheme" title="Template:Routing scheme"><span title="View this template" style="">v</span></a></li> <li class="nv-talk"><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Template_talk:Routing_scheme" title="Template talk:Routing scheme"><span title="Discuss this template" style="">t</span></a></li> <li class="nv-edit"><a class="external text" href="//web.archive.org/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Template:Routing_scheme&action=edit"><span title="Edit this template" style="">e</span></a></li> </ul> </div> </td> </tr> </table> <p>Routing schemes differ in their delivery semantics:</p> <ul> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Unicast" title="Unicast">unicast</a> delivers a message to a single specific node</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Broadcasting_(computing)" title="Broadcasting (computing)" class="mw-redirect">broadcast</a> delivers a message to all nodes in the network</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Multicast" title="Multicast">multicast</a> delivers a message to a group of nodes that have expressed interest in receiving the message</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Anycast" title="Anycast">anycast</a> delivers a message to anyone out of a group of nodes, typically the one nearest to the source</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Geocast" title="Geocast">geocast</a> delivers a message to a geographic area</li> </ul> <p>Unicast is the dominant form of message delivery on the Internet. This article focuses on unicast routing algorithms.</p> <h2><span class="mw-headline" id="Topology_distribution">Topology distribution</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=2" title="Edit section: Topology distribution">edit</a><span class="mw-editsection-bracket">]</span></span></h2> <p>In <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Static_routing" title="Static routing">static routing</a> (or non-adaptive routing), small networks may use manually configured routing tables. Larger networks have complex <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Network_topology" title="Network topology">topologies</a> that can change rapidly, making the manual construction of routing tables unfeasible. Nevertheless, most of the <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Public_Switched_Telephone_Network" title="Public Switched Telephone Network" class="mw-redirect">public switched telephone network</a> (PSTN) uses pre-computed routing tables, with fallback routes if the most direct route becomes blocked (see <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Routing_in_the_PSTN" title="Routing in the PSTN">routing in the PSTN</a>). <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Adaptive_routing" title="Adaptive routing">Adaptive routing</a>, or dynamic routing, attempts to solve this problem by constructing routing tables automatically, based on information carried by <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Routing_protocol" title="Routing protocol">routing protocols</a>, allowing the network to act nearly autonomously in avoiding network failures and blockages.</p> <p>Examples of adaptive-routing algorithms are the Routing Information Protocol (<a href="/web/20150318213050/http://en.wikipedia.org/wiki/Routing_Information_Protocol" title="Routing Information Protocol">RIP</a>) and the Open-Shortest-Path-First protocol (<a href="/web/20150318213050/http://en.wikipedia.org/wiki/OSPF" title="OSPF" class="mw-redirect">OSPF</a>). Adaptive routing dominates the Internet. However, the configuration of the routing protocols often requires a skilled touch; networking technology has not developed to the point of the complete automation of routing.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (October 2011)">citation needed</span></a></i>]</sup></p> <h3><span class="mw-headline" id="Distance_vector_algorithms">Distance vector algorithms</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=3" title="Edit section: Distance vector algorithms">edit</a><span class="mw-editsection-bracket">]</span></span></h3> <div class="hatnote relarticle mainarticle">Main article: <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Distance-vector_routing_protocol" title="Distance-vector routing protocol">Distance-vector routing protocol</a></div> <p>Distance vector algorithms use the <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Bellman%E2%80%93Ford_algorithm" title="Bellman–Ford algorithm">Bellman–Ford algorithm</a>. This approach assigns a <i>cost</i> number to each of the links between each node in the network. Nodes will send information from point A to point B via the path that results in the lowest <i>total cost</i> (i.e. the sum of the costs of the links between the nodes used).</p> <p>The algorithm operates in a very simple manner. When a node first starts, it only knows of its immediate neighbours, and the direct cost involved in reaching them. (This information — the list of destinations, the total cost to each, and the <i>next hop</i> to send data to get there — makes up the routing table, or <i>distance table</i>.) Each node, on a regular basis, sends to each neighbour node its own current assessment of the total cost to get to all the destinations it knows of. The neighbouring nodes examine this information and compare it to what they already 'know'; anything that represents an improvement on what they already have, they insert in their own routing table(s). Over time, all the nodes in the network will discover the best next hop for all destinations, and the best total cost.</p> <p>When one network node goes down, any nodes that used it as their next hop discard the entry, and create new routing-table information. These nodes convey the updated routing information to all adjacent nodes, which in turn repeat the process. Eventually all the nodes in the network receive the updates, and discover new paths to all the destinations they can still "reach". e.g. RIPV1,RIPV2</p> <h3><span class="mw-headline" id="Link-state_algorithms">Link-state algorithms</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=4" title="Edit section: Link-state algorithms">edit</a><span class="mw-editsection-bracket">]</span></span></h3> <div class="hatnote relarticle mainarticle">Main article: <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Link-state_routing_protocol" title="Link-state routing protocol">Link-state routing protocol</a></div> <p>When applying link-state algorithms, a <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Graph_(mathematics)" title="Graph (mathematics)">graphical</a> <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Map" title="Map">map</a> of the network is the fundamental data used for each node. To produce its map, each node floods the entire network with information about the other nodes it can connect to. Each node then independently assembles this information into a map. Using this map, each router independently determines the least-cost path from itself to every other node using a standard <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Shortest_path_problem" title="Shortest path problem">shortest paths</a> algorithm such as <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Dijkstra%27s_algorithm" title="Dijkstra's algorithm">Dijkstra's algorithm</a>. The result is a <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Tree_(graph_theory)" title="Tree (graph theory)">tree graph</a> rooted at the current node, such that the path through the tree from the root to any other node is the least-cost path to that node. This tree then serves to construct the routing table, which specifies the best next hop to get from the current node to any other node.</p> <h3><span class="mw-headline" id="Optimised_Link_State_Routing_algorithm">Optimised Link State Routing algorithm</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=5" title="Edit section: Optimised Link State Routing algorithm">edit</a><span class="mw-editsection-bracket">]</span></span></h3> <div class="hatnote relarticle mainarticle">Main article: <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Optimized_Link_State_Routing_Protocol" title="Optimized Link State Routing Protocol">Optimized Link State Routing Protocol</a></div> <p>A link-state routing algorithm optimised for <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Mobile_ad_hoc_network" title="Mobile ad hoc network">mobile ad hoc networks</a> is the <i>Optimised Link State Routing Protocol (OLSR)</i>.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span>[</span>1<span>]</span></a></sup> OLSR is proactive; it uses Hello and Topology Control (TC) messages to discover and disseminate link state information through the <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Mobile_ad_hoc_network" title="Mobile ad hoc network">mobile ad hoc network</a>. Using Hello messages, each node discovers 2-hop neighbor information and elects a set of <i><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Multipoint_relay" title="Multipoint relay">multipoint relays</a></i> (MPRs). MPRs distinguish OLSR from other link state routing protocols.</p> <h3><span class="mw-headline" id="Path_vector_protocol">Path vector protocol</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=6" title="Edit section: Path vector protocol">edit</a><span class="mw-editsection-bracket">]</span></span></h3> <div class="hatnote relarticle mainarticle">Main article: <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Path_vector_protocol" title="Path vector protocol">Path vector protocol</a></div> <p>Distance vector and link state routing are both intra-domain routing protocols. They are used inside an <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Autonomous_system_(Internet)" title="Autonomous system (Internet)">autonomous system</a>, but not between autonomous systems. Both of these routing protocols become intractable in large networks and cannot be used in <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Inter-domain" title="Inter-domain">Inter-domain</a> routing. Distance vector routing is subject to instability if there are more than a few hops in the domain. Link state routing needs huge amount of resources to calculate routing tables. It also creates heavy traffic due to flooding.</p> <p>Path vector routing is used for inter-domain routing. It is similar to distance vector routing. In path vector routing we assume there is one node (there can be many) in each autonomous system which acts on behalf of the entire autonomous system. This node is called the speaker node. The speaker node creates a routing table and advertises it to neighboring speaker nodes in neighboring autonomous systems. The idea is the same as distance vector routing except that only speaker nodes in each autonomous system can communicate with each other. The speaker node advertises the path, not the metric, of the nodes in its autonomous system or other autonomous systems. Path vector routing is discussed in <a class="external mw-magiclink-rfc" rel="nofollow" href="//web.archive.org/web/20150318213050/http://tools.ietf.org/html/rfc1322">RFC 1322</a>; the path vector routing algorithm is somewhat similar to the distance vector algorithm in the sense that each border router advertises the destinations it can reach to its neighboring router. However, instead of advertising networks in terms of a destination and the distance to that destination, networks are advertised as destination addresses and path descriptions to reach those destinations. A route is defined as a pairing between a destination and the attributes of the path to that destination, thus the name, path vector routing, where the routers receive a vector that contains paths to a set of destinations. The path, expressed in terms of the domains (or confederations) traversed so far, is carried in a special path attribute that records the sequence of routing domains through which the reachability information has passed.</p> <h2><span class="mw-headline" id="Path_selection">Path selection</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=7" title="Edit section: Path selection">edit</a><span class="mw-editsection-bracket">]</span></span></h2> <p>Path selection involves applying a <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Metrics_(networking)" title="Metrics (networking)">routing metric</a> to multiple routes, in order to select (or predict) the best route.</p> <p>In computer networking, the metric is computed by a routing algorithm, and can cover information such as <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Bandwidth_(computing)" title="Bandwidth (computing)">bandwidth</a>, <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Network_delay" title="Network delay">network delay</a>, <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Hop_count" title="Hop count" class="mw-redirect">hop count</a>, path cost, load, <a href="/web/20150318213050/http://en.wikipedia.org/wiki/MTU_(networking)" title="MTU (networking)" class="mw-redirect">MTU</a> (maximum transmission unit), reliability, and communication cost (see e.g. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20150318213050/http://rainer.baumann.info/public/tik262.pdf">this survey</a> for a list of proposed routing metrics). The routing table stores only the best possible routes, while <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Link-state" title="Link-state" class="mw-redirect">link-state</a> or topological databases may store all other information as well.</p> <p>Because a routing metric is specific to a given routing protocol, multi-protocol routers must use some external heuristic in order to select between routes learned from different routing protocols. <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Cisco" title="Cisco" class="mw-redirect">Cisco</a> routers, for example, attribute a value known as the <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Administrative_distance" title="Administrative distance">administrative distance</a> to each route, where smaller administrative distances indicate routes learned from a supposedly more reliable protocol.</p> <p>A local network administrator, in special cases, can set up host-specific routes to a particular device which provides more control over network usage, permits testing and better overall security. This can come in handy when debugging network connections or routing tables.</p> <p>In some small systems, a single central device decides ahead of time the complete path of every packet. In some other small systems, whichever edge device injects a packet into the network decides ahead of the time complete path of that particular packet. In both of these systems, that route-planning device needs to know a lot of information about what devices are connected to the network and how they are connected to each other. Once it has this information, it can use an algorithm such as <a href="/web/20150318213050/http://en.wikipedia.org/wiki/A*_search_algorithm" title="A* search algorithm">A* search algorithm</a> to find the best path.</p> <p>In high-speed systems, there are so many packets transmitted every second that it is infeasible for a single device to calculate the complete path for each and every packet. Early high-speed systems dealt with this by setting up a <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Circuit_switching" title="Circuit switching">circuit switching</a> <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Relay_channel" title="Relay channel">relay channel</a> once for the first packet between some source and some destination; later packets between that same source and that same destination continue to follow the same path without recalculating until the channel <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Teardown_(communications)" title="Teardown (communications)" class="mw-redirect">teardown</a>. Later high-speed systems inject packets into the network without any one device ever calculating a complete path for that packet -- multiple agents.</p> <p>In large systems, there are so many connections between devices, and those connections change so frequently, that it is infeasible for any one device to even know how all the devices are connected to each other, much less calculate a complete path through them. Such systems generally use <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Hop_(networking)#Next_hop" title="Hop (networking)">next-hop</a> routing.</p> <h2><span class="mw-headline" id="Multiple_agents">Multiple agents</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=8" title="Edit section: Multiple agents">edit</a><span class="mw-editsection-bracket">]</span></span></h2> <p>In some networks, routing is complicated by the fact that no single entity is responsible for selecting paths; instead, multiple entities are involved in selecting paths or even parts of a single path. Complications or inefficiency can result if these entities choose paths to optimize their own objectives, which may conflict with the objectives of other participants.</p> <p>A classic example involves traffic in a road system, in which each driver picks a path which minimizes their own travel time. With such routing, the <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Nash_equilibrium" title="Nash equilibrium">equilibrium</a> routes can be longer than optimal for all drivers. In particular, <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Braess_paradox" title="Braess paradox" class="mw-redirect">Braess paradox</a> shows that adding a new road can <i>lengthen</i> travel times for all drivers.</p> <p>In another model, for example, used for routing <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Automated_guided_vehicle" title="Automated guided vehicle">automated guided vehicles</a> (AGVs) on a terminal, reservations are made for each vehicle to prevent simultaneous use of the same part of an infrastructure. This approach is also referred to as context-aware routing.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span>[</span>2<span>]</span></a></sup></p> <p>The Internet is partitioned into <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Autonomous_system_(Internet)" title="Autonomous system (Internet)">autonomous systems</a> (ASs) such as <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Internet_service_provider" title="Internet service provider">internet service providers</a> (ISPs), each of which has control over routes involving its network, at multiple levels. First, AS-level paths are selected via the <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Border_Gateway_Protocol" title="Border Gateway Protocol">BGP</a> protocol, which produces a sequence of ASs through which packets will flow. Each AS may have multiple paths, offered by neighboring ASs, from which to choose. Its decision often involves business relationships with these neighboring ASs,<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span>[</span>3<span>]</span></a></sup> which may be unrelated to path quality or latency. Second, once an AS-level path has been selected, there are often multiple corresponding router-level paths, in part because two ISPs may be connected in multiple locations. In choosing the single router-level path, it is common practice for each ISP to employ <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Hot-potato_routing" title="Hot-potato routing" class="mw-redirect">hot-potato routing</a>: sending traffic along the path that minimizes the distance through the ISP's own network—even if that path lengthens the total distance to the destination.</p> <p>Consider two ISPs, <i>A</i> and <i>B</i>, which each have a presence in <a href="/web/20150318213050/http://en.wikipedia.org/wiki/New_York_City" title="New York City">New York</a>, connected by a fast link with latency 5 <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Millisecond" title="Millisecond">ms</a>; and which each have a presence in <a href="/web/20150318213050/http://en.wikipedia.org/wiki/London" title="London">London</a> connected by a 5 ms link. Suppose both ISPs have trans-Atlantic links connecting their two networks, but <i>A</i>'s link has latency 100 ms and B's has latency 120 ms. When routing a message from a source in <i>A</i>'s London network to a destination in <i>B</i>'s New York network, <i>A</i> may choose to immediately send the message to <i>B</i> in London. This saves <i>A</i> the work of sending it along an expensive trans-Atlantic link, but causes the message to experience latency 125 ms when the other route would have been 20 ms faster.</p> <p>A 2003 measurement study of Internet routes found that, between pairs of neighboring ISPs, more than 30% of paths have inflated latency due to hot-potato routing, with 5% of paths being delayed by at least 12 ms. Inflation due to AS-level path selection, while substantial, was attributed primarily to BGP's lack of a mechanism to directly optimize for latency, rather than to selfish routing policies. It was also suggested that, were an appropriate mechanism in place, ISPs would be willing to cooperate to reduce latency rather than use hot-potato routing.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span>[</span>4<span>]</span></a></sup></p> <p>Such a mechanism was later published by the same authors, first for the case of two ISPs<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span>[</span>5<span>]</span></a></sup> and then for the global case.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span>[</span>6<span>]</span></a></sup></p> <h2><span class="mw-headline" id="Route_analytics">Route analytics</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=9" title="Edit section: Route analytics">edit</a><span class="mw-editsection-bracket">]</span></span></h2> <p>As the Internet and IP networks become <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Mission_critical" title="Mission critical">mission critical</a> business tools, there has been increased interest in techniques and methods to monitor the routing posture of networks. Incorrect routing or routing issues cause undesirable performance degradation, <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Route_flapping" title="Route flapping">flapping</a> and/or downtime. Monitoring routing in a network is achieved using <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Route_analytics" title="Route analytics">route analytics</a> tools and techniques.</p> <h2><span class="mw-headline" id="See_also">See also</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=10" title="Edit section: See also">edit</a><span class="mw-editsection-bracket">]</span></span></h2> <h3><span class="mw-headline" id="Routing_algorithms_and_techniques">Routing algorithms and techniques</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=11" title="Edit section: Routing algorithms and techniques">edit</a><span class="mw-editsection-bracket">]</span></span></h3> <div class="div-col columns column-count column-count-2" style="-moz-column-count: 2; -webkit-column-count: 2; column-count: 2;"> <ul> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Adaptive_routing" title="Adaptive routing">Adaptive routing</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Deflection_routing" title="Deflection routing">Deflection routing</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Edge_Disjoint_Shortest_Pair_Algorithm" title="Edge Disjoint Shortest Pair Algorithm" class="mw-redirect">Edge Disjoint Shortest Pair Algorithm</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Dijkstra%27s_algorithm" title="Dijkstra's algorithm">Dijkstra's algorithm</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Flood_search_routing" title="Flood search routing">Flood search routing</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Fuzzy_routing" title="Fuzzy routing">Fuzzy routing</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Geographic_routing" title="Geographic routing">Geographic routing</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Heuristic_routing" title="Heuristic routing">Heuristic routing</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Hierarchical_routing" title="Hierarchical routing">Hierarchical routing</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/IP_forwarding_algorithm" title="IP forwarding algorithm">IP Forwarding Algorithm</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Multipath_routing" title="Multipath routing">Multipath routing</a> <ul> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Shortest_Path_Bridging" title="Shortest Path Bridging" class="mw-redirect">Shortest Path Bridging</a></li> </ul> </li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Overlay_network" title="Overlay network">Overlay network</a> routing schemes <ul> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Key-based_routing" title="Key-based routing">Key-based routing</a> (KBR)</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Decentralized_object_location_and_routing" title="Decentralized object location and routing">Decentralized object location and routing</a> (DOLR)</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Distributed_hash_table" title="Distributed hash table">Distributed hash table</a> (DHT)</li> </ul> </li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Path_computation_element" title="Path computation element">Path computation element</a> (PCE)</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Policy-based_routing" title="Policy-based routing">Policy-based routing</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Quality_of_Service" title="Quality of Service" class="mw-redirect">Quality of Service</a> in routing</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Static_routing" title="Static routing">Static routing</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Wormhole_routing" title="Wormhole routing" class="mw-redirect">Wormhole routing</a></li> </ul> </div> <h3><span class="mw-headline" id="Routing_in_specific_networks">Routing in specific networks</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=12" title="Edit section: Routing in specific networks">edit</a><span class="mw-editsection-bracket">]</span></span></h3> <ul> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Open_Source_Routing_Machine" title="Open Source Routing Machine">Open Source Routing Machine</a> (Road map routing)</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Route_assignment" title="Route assignment">Route assignment</a> in transportation networks</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Routing_in_the_PSTN" title="Routing in the PSTN">Routing in the PSTN</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Small_world_routing" title="Small world routing" class="mw-redirect">Small world routing</a> – the internet is approximately a small world network</li> </ul> <h3><span class="mw-headline" id="Routing_protocols">Routing protocols</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=13" title="Edit section: Routing protocols">edit</a><span class="mw-editsection-bracket">]</span></span></h3> <ul> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Routing_protocol" title="Routing protocol">Routing protocol</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Classless_inter-domain_routing" title="Classless inter-domain routing" class="mw-redirect">Classless inter-domain routing</a> (CIDR)</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Multiprotocol_Label_Switching" title="Multiprotocol Label Switching">MPLS</a> routing</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Asynchronous_Transfer_Mode" title="Asynchronous Transfer Mode">ATM</a> routing</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/RPSL" title="RPSL" class="mw-redirect">RPSL</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/RSMLT" title="RSMLT" class="mw-redirect">RSMLT</a></li> <li>Routing in <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Optical_mesh_network" title="Optical mesh network">optical mesh networks</a></li> </ul> <h3><span class="mw-headline" id="Alternative_methods_for_network_data_flow">Alternative methods for network data flow</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=14" title="Edit section: Alternative methods for network data flow">edit</a><span class="mw-editsection-bracket">]</span></span></h3> <ul> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Peer-to-peer" title="Peer-to-peer">Peer-to-peer</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Network_coding" title="Network coding" class="mw-redirect">Network coding</a></li> </ul> <h3><span class="mw-headline" id="Router_software_and_suites">Router software and suites</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=15" title="Edit section: Router software and suites">edit</a><span class="mw-editsection-bracket">]</span></span></h3> <ul> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/GNU_Zebra" title="GNU Zebra">GNU Zebra</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Quagga_(software)" title="Quagga (software)">Quagga (software)</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Iproute2" title="Iproute2">Iproute2</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Bird_Internet_routing_daemon" title="Bird Internet routing daemon">Bird Internet routing daemon</a></li> </ul> <h3><span class="mw-headline" id="Router_platforms">Router platforms</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=16" title="Edit section: Router platforms">edit</a><span class="mw-editsection-bracket">]</span></span></h3> <ul> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Network_operating_system" title="Network operating system">Network operating system</a> – NOS</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/XORP" title="XORP">XORP</a> – the eXtensible Open Router Platform</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/FTOS" title="FTOS">FTOS</a> – Dell's Force 10 firmware family</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Junos" title="Junos">Junos</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Cisco_IOS" title="Cisco IOS">Cisco IOS</a> - Cisco's Internetwork Operating System</li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/NX-OS" title="NX-OS">NX-OS</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/CatOS" title="CatOS" class="mw-redirect">CatOS</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=LCOS_(operating_system)&action=edit&redlink=1" class="new" title="LCOS (operating system) (page does not exist)">LCOS</a> - Lancom Operating System</li> </ul> <h2><span class="mw-headline" id="References">References</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=17" title="Edit section: References">edit</a><span class="mw-editsection-bracket">]</span></span></h2> <table class="metadata plainlinks ambox ambox-style ambox-More_footnotes" role="presentation"> <tr> <td class="mbox-image"> <div style="width:52px"><img alt="" src="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/a/a4/Text_document_with_red_question_mark.svg/40px-Text_document_with_red_question_mark.svg.png" width="40" height="40" srcset="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/a/a4/Text_document_with_red_question_mark.svg/60px-Text_document_with_red_question_mark.svg.png 1.5x, //web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/a/a4/Text_document_with_red_question_mark.svg/80px-Text_document_with_red_question_mark.svg.png 2x" data-file-width="48" data-file-height="48"/></div> </td> <td class="mbox-text"><span class="mbox-text-span">This article includes a <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Wikipedia:Citing_sources" title="Wikipedia:Citing sources">list of references</a>, but <b>its sources remain unclear</b> because it has <b>insufficient <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Wikipedia:Citing_sources#Inline_citations" title="Wikipedia:Citing sources">inline citations</a></b>. <span class="hide-when-compact">Please help to <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Wikipedia:WikiProject_Fact_and_Reference_Check" title="Wikipedia:WikiProject Fact and Reference Check">improve</a> this article by <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Wikipedia:When_to_cite" title="Wikipedia:When to cite">introducing</a> more precise citations.</span> <small><i>(October 2011)</i></small></span></td> </tr> </table> <p><b>Notes</b></p> <div class="reflist" style="list-style-type: decimal;"> <ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text"><a class="external mw-magiclink-rfc" rel="nofollow" href="//web.archive.org/web/20150318213050/http://tools.ietf.org/html/rfc3626">RFC 3626</a></span></li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text">Jonne Zutt, Arjan J.C. van Gemund, Mathijs M. de Weerdt, and Cees Witteveen (2010). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20150318213050/http://www.st.ewi.tudelft.nl/~mathijs/publications/intinfra09.pdf">Dealing with Uncertainty in Operational Transport Planning</a>. In R.R. Negenborn and Z. Lukszo and H. Hellendoorn (Eds.) Intelligent Infrastructures, Ch. 14, pp. 355–382. Springer.</span></li> <li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text">Matthew Caesar and <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Jennifer_Rexford" title="Jennifer Rexford">Jennifer Rexford</a>. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20150318213050/http://www.cs.princeton.edu/~jrex/papers/policies.pdf">BGP routing policies in ISP networks</a>. IEEE Network Magazine, special issue on Interdomain Routing, Nov/Dec 2005.</span></li> <li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text">Neil Spring, Ratul Mahajan, and Thomas Anderson. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20150318213050/http://www.cs.washington.edu/research/networking/rocketfuel/papers/sigcomm2003.pdf">Quantifying the Causes of Path Inflation</a>. Proc. <a href="/web/20150318213050/http://en.wikipedia.org/wiki/SIGCOMM" title="SIGCOMM">SIGCOMM</a> 2003.</span></li> <li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text">Ratul Mahajan, David Wetherall, and Thomas Anderson. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20150318213050/http://research.microsoft.com/en-us/um/people/ratul/papers/nsdi2005-nexit.pdf">Negotiation-Based Routing Between Neighboring ISPs</a>. Proc. <a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=NSDI&action=edit&redlink=1" class="new" title="NSDI (page does not exist)">NSDI</a> 2005.</span></li> <li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text">Ratul Mahajan, David Wetherall, and Thomas Anderson. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20150318213050/http://research.microsoft.com/en-us/um/people/ratul/papers/nsdi2007-wiser.pdf">Mutually Controlled Routing with Independent ISPs</a>. Proc. <a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=NSDI&action=edit&redlink=1" class="new" title="NSDI (page does not exist)">NSDI</a> 2007.</span></li> </ol> </div> <p><b>Sources</b></p> <div class="refbegin" style=""> <ul> <li><span class="citation book">Ash, Gerald (1997). <i>Dynamic Routing in Telecommunication Networks</i>. McGraw–Hill. <a href="/web/20150318213050/http://en.wikipedia.org/wiki/International_Standard_Book_Number" title="International Standard Book Number">ISBN</a> <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Special:BookSources/0-07-006414-8" title="Special:BookSources/0-07-006414-8">0-07-006414-8</a>.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ARouting&rft.au=Ash%2C+Gerald&rft.aulast=Ash%2C+Gerald&rft.btitle=Dynamic+Routing+in+Telecommunication+Networks&rft.date=1997&rft.genre=book&rft.isbn=0-07-006414-8&rft.pub=McGraw%E2%80%93Hill&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook" class="Z3988"><span style="display:none;"> </span></span></li> <li><span class="citation book">Doyle, Jeff and Carroll, Jennifer (2005). <i>Routing TCP/IP, Volume I, Second Ed</i>. Cisco Press. <a href="/web/20150318213050/http://en.wikipedia.org/wiki/International_Standard_Book_Number" title="International Standard Book Number">ISBN</a> <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Special:BookSources/1-58705-202-4" title="Special:BookSources/1-58705-202-4">1-58705-202-4</a>.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ARouting&rft.au=Doyle%2C+Jeff+and+Carroll%2C+Jennifer&rft.aulast=Doyle%2C+Jeff+and+Carroll%2C+Jennifer&rft.btitle=Routing+TCP%2FIP%2C+Volume+I%2C+Second+Ed.&rft.date=2005&rft.genre=book&rft.isbn=1-58705-202-4&rft.pub=Cisco+Press&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook" class="Z3988"><span style="display:none;"> </span></span><a rel="nofollow" class="external text" href="https://web.archive.org/web/20150318213050/http://www.ciscopress.com/title/1587052024">Ciscopress ISBN 1-58705-202-4</a></li> <li><span class="citation book">Doyle, Jeff and Carroll, Jennifer (2001). <i>Routing TCP/IP, Volume II,</i>. Cisco Press. <a href="/web/20150318213050/http://en.wikipedia.org/wiki/International_Standard_Book_Number" title="International Standard Book Number">ISBN</a> <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Special:BookSources/1-57870-089-2" title="Special:BookSources/1-57870-089-2">1-57870-089-2</a>.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ARouting&rft.au=Doyle%2C+Jeff+and+Carroll%2C+Jennifer&rft.aulast=Doyle%2C+Jeff+and+Carroll%2C+Jennifer&rft.btitle=Routing+TCP%2FIP%2C+Volume+II%2C&rft.date=2001&rft.genre=book&rft.isbn=1-57870-089-2&rft.pub=Cisco+Press&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook" class="Z3988"><span style="display:none;"> </span></span><a rel="nofollow" class="external text" href="https://web.archive.org/web/20150318213050/http://www.ciscopress.com/title/1578700892">Ciscopress ISBN 1-57870-089-2</a></li> <li><span class="citation book">Huitema, Christian (2000). <i>Routing in the Internet, Second Ed</i>. Prentice–Hall. <a href="/web/20150318213050/http://en.wikipedia.org/wiki/International_Standard_Book_Number" title="International Standard Book Number">ISBN</a> <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Special:BookSources/0-321-22735-2" title="Special:BookSources/0-321-22735-2">0-321-22735-2</a>.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ARouting&rft.au=Huitema%2C+Christian&rft.aulast=Huitema%2C+Christian&rft.btitle=Routing+in+the+Internet%2C+Second+Ed.&rft.date=2000&rft.genre=book&rft.isbn=0-321-22735-2&rft.pub=Prentice%E2%80%93Hall&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook" class="Z3988"><span style="display:none;"> </span></span></li> <li><span class="citation book">Kurose, James E. and Ross, Keith W. (2004). <i>Computer Networking, Third Ed</i>. Benjamin/Cummings. <a href="/web/20150318213050/http://en.wikipedia.org/wiki/International_Standard_Book_Number" title="International Standard Book Number">ISBN</a> <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Special:BookSources/0-321-22735-2" title="Special:BookSources/0-321-22735-2">0-321-22735-2</a>.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ARouting&rft.au=Kurose%2C+James+E.+and+Ross%2C+Keith+W.&rft.aulast=Kurose%2C+James+E.+and+Ross%2C+Keith+W.&rft.btitle=Computer+Networking%2C+Third+Ed.&rft.date=2004&rft.genre=book&rft.isbn=0-321-22735-2&rft.pub=Benjamin%2FCummings&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook" class="Z3988"><span style="display:none;"> </span></span></li> <li><span class="citation book">Medhi, Deepankar and Ramasamy, Karthikeyan (2007). <i>Network Routing: Algorithms, Protocols, and Architectures</i>. Morgan Kaufmann. <a href="/web/20150318213050/http://en.wikipedia.org/wiki/International_Standard_Book_Number" title="International Standard Book Number">ISBN</a> <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Special:BookSources/0-12-088588-3" title="Special:BookSources/0-12-088588-3">0-12-088588-3</a>.</span><span title="ctx_ver=Z39.88-2004&rfr_id=info%3Asid%2Fen.wikipedia.org%3ARouting&rft.aulast=Medhi%2C+Deepankar+and+Ramasamy%2C+Karthikeyan&rft.au=Medhi%2C+Deepankar+and+Ramasamy%2C+Karthikeyan&rft.btitle=Network+Routing%3A+Algorithms%2C+Protocols%2C+and+Architectures&rft.date=2007&rft.genre=book&rft.isbn=0-12-088588-3&rft.pub=Morgan+Kaufmann&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook" class="Z3988"><span style="display:none;"> </span></span></li> </ul> </div> <h2><span class="mw-headline" id="External_links">External links</span><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Routing&action=edit&section=18" title="Edit section: External links">edit</a><span class="mw-editsection-bracket">]</span></span></h2> <table class="mbox-small plainlinks" style="border:1px solid #aaa;background-color:#f9f9f9"> <tr> <td class="mbox-image"><img alt="" src="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Wikiversity-logo.svg/40px-Wikiversity-logo.svg.png" width="40" height="32" srcset="//web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Wikiversity-logo.svg/60px-Wikiversity-logo.svg.png 1.5x, //web.archive.org/web/20150318213050im_/http://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Wikiversity-logo.svg/80px-Wikiversity-logo.svg.png 2x" data-file-width="1000" data-file-height="800"/></td> <td class="mbox-text plainlist">Wikiversity has learning materials about <i><b><a href="//web.archive.org/web/20150318213050/http://en.wikiversity.org/wiki/Routing" class="extiw" title="v:Routing">Routing</a></b></i></td> </tr> </table> <ul> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20150318213050/http://wiki.uni.lu/secan-lab/Count-To-Infinity+Problem.html">Count-To-Infinity Problem</a><sup class="noprint Inline-Template"><span style="white-space: nowrap;">[<i><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Wikipedia:Link_rot" title="Wikipedia:Link rot"><span title=" since October 2014">dead link</span></a></i>]</span></sup></li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20150318213050/http://wwwlehre.dhbw-stuttgart.de/~schulte/htme/55024.htm#HDR3">"Stability Features"</a> are ways of avoiding the "count to infinity" problem.</li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20150318213050/http://www.cisco.com/web/about/ciscoitatwork/case_studies/routing.html">Cisco IT Case Studies</a><sup class="noprint Inline-Template"><span style="white-space: nowrap;">[<i><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Wikipedia:Link_rot" title="Wikipedia:Link rot"><span title=" since October 2014">dead link</span></a></i>]</span></sup> about Routing and Switching</li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20150318213050/http://www.eventhelix.com/Realtimemantra/Networking/ip_routing.htm">good example at event-helix</a></li> </ul> <table class="navbox" style="border-spacing:0"> <tr> <td style="padding:2px"> <table class="nowraplinks collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"> <tr> <th scope="col" class="navbox-title" colspan="2"> <div class="plainlinks hlist navbar mini"> <ul> <li class="nv-view"><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Template:Routing_protocols" title="Template:Routing protocols"><span title="View this template" style=";;background:none transparent;border:none;">v</span></a></li> <li class="nv-talk"><a href="/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Template_talk:Routing_protocols&action=edit&redlink=1" class="new" title="Template talk:Routing protocols (page does not exist)"><span title="Discuss this template" style=";;background:none transparent;border:none;">t</span></a></li> <li class="nv-edit"><a class="external text" href="//web.archive.org/web/20150318213050/http://en.wikipedia.org/w/index.php?title=Template:Routing_protocols&action=edit"><span title="Edit this template" style=";;background:none transparent;border:none;">e</span></a></li> </ul> </div> <div style="font-size:110%"><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Routing_protocol" title="Routing protocol">Routing protocols</a></div> </th> </tr> <tr style="height:2px"> <td colspan="2"></td> </tr> <tr> <th scope="row" class="navbox-group">General</th> <td class="navbox-list navbox-odd hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px"> <div style="padding:0em 0.25em"> <ul> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Babel_(protocol)" title="Babel (protocol)">Babel</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/B.A.T.M.A.N." title="B.A.T.M.A.N.">B.A.T.M.A.N.</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Border_Gateway_Protocol" title="Border Gateway Protocol">BGP</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/IS-IS" title="IS-IS">IS-IS</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Optimized_Link_State_Routing_Protocol" title="Optimized Link State Routing Protocol">OLSR</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Open_Shortest_Path_First" title="Open Shortest Path First">OSPF</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Routing_Information_Protocol" title="Routing Information Protocol">RIP</a></li> </ul> </div> </td> </tr> <tr style="height:2px"> <td colspan="2"></td> </tr> <tr> <th scope="row" class="navbox-group">Vendor-driven</th> <td class="navbox-list navbox-even hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px"> <div style="padding:0em 0.25em"> <ul> <li>(Cisco) <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Interior_Gateway_Routing_Protocol" title="Interior Gateway Routing Protocol">IGRP</a> / <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Enhanced_Interior_Gateway_Routing_Protocol" title="Enhanced Interior Gateway Routing Protocol">EIGRP</a></li> <li>(Nortel) <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Split_multi-link_trunking" title="Split multi-link trunking">SMLT</a> / <a href="/web/20150318213050/http://en.wikipedia.org/wiki/R-SMLT" title="R-SMLT">R-SMLT</a> / <a href="/web/20150318213050/http://en.wikipedia.org/wiki/Distributed_Split_Multi-Link_Trunking" title="Distributed Split Multi-Link Trunking">DSMLT</a></li> </ul> </div> </td> </tr> <tr style="height:2px"> <td colspan="2"></td> </tr> <tr> <th scope="row" class="navbox-group">Special-purpose</th> <td class="navbox-list navbox-odd hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px"> <div style="padding:0em 0.25em"> <ul> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Collection_Tree_Protocol" title="Collection Tree Protocol">CTP</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Constrained_Shortest_Path_First" title="Constrained Shortest Path First">CSPF</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Distance_Vector_Multicast_Routing_Protocol" title="Distance Vector Multicast Routing Protocol">DVMRP</a></li> </ul> </div> </td> </tr> <tr style="height:2px"> <td colspan="2"></td> </tr> <tr> <th scope="row" class="navbox-group">Defunct</th> <td class="navbox-list navbox-even hlist" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px"> <div style="padding:0em 0.25em"> <ul> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Border_Gateway_Multicast_Protocol" title="Border Gateway Multicast Protocol">BGMP</a></li> <li><a href="/web/20150318213050/http://en.wikipedia.org/wiki/Exterior_Gateway_Protocol" title="Exterior Gateway Protocol">EGP</a></li> </ul> </div> </td> </tr> </table> </td> </tr> </table>    <noscript><img src="//web.archive.org/web/20150318213050im_/http://en.wikipedia.org/wiki/Special:CentralAutoLogin/start?type=1x1" alt="" title="" width="1" height="1" style="border: none; position: absolute;"/></noscript></div> <div class="printfooter"> Retrieved from "<a dir="ltr" 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