Routers that use distance-vector protocol determine the distance between themselves and a destination. The best route for [[Internet Protocol]] [[]] that carry [[data]] acrossthrough a [[data network]] is measured in terms of the numbers of [[Router (computing)|routers]] (hops) a packet has to pass through 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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==Count to infinity problem==
The [[Bellman–Ford algorithm]] does not prevent [[routing loop]]s from happening and suffers from the '''count to infinity problem'''. The core of the count- to- infinity problem is that if A tells B that it has a path somewhere, there is no way for B to know if the path has B as a part of it. To see the problem, imagine a subnet connected like A–B–C–D–E–F, and let the metric between the routers be "number of jumps". Now suppose that A is taken offline. In the vector-update-process B notices that the route to A, which was distance 1, is down – B does not receive the vector update from A. The problem is, B also gets an update from C, and C is still not aware of the fact that A is down – so it tells B that A is only two jumps from C (C to B to A). Since B doesn't know that the path from C to A is through itself (B), it updates its table with the new value "B to A = 2 + 1". Later on, B forwards the update to C and due to the fact that A is reachable through B (From C's point of view), C decides to update its table to "C to A = 3 + 1". This slowly propagates through the network until it becomes infinity (in which case the algorithm corrects itself, due to the relaxation property of Bellman-Ford).
===Workarounds and solutions===
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==Further reading==
* [http://docwiki.cisco.com/wiki/Routing_Basics#Link-State_Versus_Distance_Vector Section "Link-State Versus Distance Vector"] {{Webarchive|url=https://web.archive.org/web/20101214043441/http://docwiki.cisco.com/wiki/Routing_Basics#Link-State_Versus_Distance_Vector |date=2010-12-14 }} in the Chapter "Routing Basics" in the [[Cisco Systems|Cisco]] "Internetworking Technology Handbook"
* [httphttps://authorscsc-knu.phptrgithub.comio/tanenbaumcn4sys-prog/books/Andrew%20S.%20Tanenbaum%20-%20Computer%20Networks.pdf Section 5.2 "Routing Algorithms"] in Chapter "5 THE NETWORK LAYER" from "Computer Networks" 4th.5th Edition by Andrew S. Tanenbaum and David J. Wetherall
