Distance-vector routing protocol: Difference between revisions

Revision as of 18:35, 15 March 2019

Revision as of 03:27, 16 April 2019

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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=|dead-url=|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 a [[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|author =Tamara Dean |publisher= Cengage Learning|year=2009 |isbn= 9781423902454|pages=274}}</ref>

The distance-vector protocol designed for use in [[wide area network]]s (WANs) is the [[Border Gateway Protocol]] (BGP). BGP is a [[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|author =Tamara Dean |publisher= Cengage Learning|year=2009 |isbn= 9781423902454|pages=274-275}}</ref>

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===Workarounds and solutions===

[[Routing Information Protocol|RIP]] uses the [[Split horizon route advertisement|split horizon]] with [[Split horizon route advertisement | poison reverse]] technique to reduce the chance of forming loops and uses a maximum number of hops to counter the 'count-to-infinity' problem. These measures avoid the formation of routing loops in some, but not all, cases.<ref>{{IETF RFC|1058}}, Section 2.2.2</ref> The addition of a ''hold time'' (refusing route updates for a few minutes after a route retraction) avoids loop formation in virtually all cases, but causes a significant increase in convergence times.

More recently, a number of loop-free distance vector protocols have been developed — notable examples are [[EIGRP]], [[DSDV]] and [[Babel (protocol)|Babel]]. These avoid loop formation in all cases, but suffer from increased complexity, and their deployment has been slowed down by the success of [[link-state routing protocol]]s such as [[OSPF]].