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The explanation for the example notes that time starts a t=0 with distance matricies from each router to its immediate neighbours, however in the example itself shows these matrices at t=1. |
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==Methodology==
Routers that use distance-vector protocol determine the distance between themselves and a destination. The best route for [[Internet Protocol]] [[Network packet|packets]] that carry [[data]] across a [[data network]] is measured in terms of the numbers of [[Router (computing)|routers]] (hops) a packet has to pass to reach its destination network. Additionally some distance-vector protocols take into account other traffic information, such as [[network latency]]. To establish the best route, routers regularly exchange information with neighbouring routers, usually their [[routing table]], hop count for a destination network and possibly other traffic related information. Routers that implement distance-vector protocol rely purely on the information provided to them by other routers, and do not assess the [[network topology]].<ref>{{Cite book|title= Network+ Guide to Networks|url= https://archive.org/details/networkguidetone00dean_142|url-access= limited|author =Tamara Dean |publisher= Cengage Learning|year=2009 |isbn= 9781423902454|pages=[https://archive.org/details/networkguidetone00dean_142/page/n294 274]}}</ref>
Distance-vector protocols update the routing tables of routers and determine the route on which a packet will be sent by the ''next hop'' which is the exit interface of the router and the IP address of the interface of the receiving router. Distance is a measure of the cost to reach a certain node. The least cost route between any two nodes is the route with minimum distance.
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== Development of distance-vector routing ==
The oldest [[routing protocol]], and the oldest distance-vector protocol, is version 1 of the [[Routing Information Protocol]] (RIPv1). RIPv1 was formally standardised in 1988.<ref>{{Cite web|url=https://tools.ietf.org/html/rfc1058.html|title=Routing Information Protocol|last=Hedrick|first=C. L.|date=|website=tools.ietf.org|language=en|rfc=1058|archive-url=|archive-date=|access-date=2019-04-16}}</ref> It establishes the shortest path across a network purely on the basis of the hops, that is numbers of routers that need to be passed to reach the destination network. RIP is an [[interior gateway protocol]], so it can be used in [[local area networks]] (LANs) on interior or border routers. Routers with RIPv1 implementation exchange their routing tables with neighbouring routers by [[Broadcasting (networking)|broadcasting]] a RIPv1 packet every 30 second into all connected networks. RIPv1 is not suitable for large networks as it limits the number of hops to 15. This hop limit was introduced to avoid routing loops, but also means that networks that are connected through more than 15 routers are unreachable.<ref>{{Cite book|title= Network+ Guide to Networks|url= https://archive.org/details/networkguidetone00dean_142|url-access= limited|author =Tamara Dean |publisher= Cengage Learning|year=2009 |isbn= 9781423902454|pages=[https://archive.org/details/networkguidetone00dean_142/page/n294 274]}}</ref>
The distance-vector protocol designed for use in [[wide area network]]s (WANs) is the [[Border Gateway Protocol]] (BGP). BGP is an [[exterior gateway protocol]] and therefore implemented on border and exterior routers on the [[Internet]]. It exchanges information between routers through a [[Transmission Control Protocol]] (TCP) session. Routers with BGP implementation determine the shortest path across a network based on a range of factors other than hops. BGP can also be configured by administrators so that certain routes are preferred or avoided. BGP is used by [[internet service providers]] (ISPs) and telecommunication companies.<ref>{{Cite book|title= Network+ Guide to Networks|url= https://archive.org/details/networkguidetone00dean_142|url-access= limited|author =Tamara Dean |publisher= Cengage Learning|year=2009 |isbn= 9781423902454|pages=
Among the distance-vector protocols that have been described as a hybrid, because it uses routing methods associated with [[link-state routing protocol]]s, is the proprietary [[Enhanced Interior Gateway Routing Protocol]] (EIGRP). It was developed by [[Cisco]] in the 1980s and was designed to offer better convergence and cause less network traffic between routers than the link-state routing protocol [[Open Shortest Path First]] (OSPF).<ref>{{Cite book|title= Network+ Guide to Networks|url= https://archive.org/details/networkguidetone00dean_142|url-access= limited|author =Tamara Dean |publisher= Cengage Learning|year=2009 |isbn= 9781423902454|pages=[https://archive.org/details/networkguidetone00dean_142/page/n295 275]}}</ref>
Another example of a distance-vector routing protocol is [[Babel (protocol)|Babel]].
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