Choose Routing Protocol

Choosing an IP routing protocol is an important step. The right protocol can make your routingoperate efficiently, and the wrong one can make your life difficult. Each protocol has its ownpros and cons, and works better in some situations than others. In this paper, we explore thestrengths and weakness of RIP, EIGRP, OSPF, and IS-IS, and discuss when it is appropriate touse each. We will evaluate each protocol in terms of five criteria:• Convergence speed• Ease of use• Network topology required• Vendor support• IPv6 support...
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Choose Routing ProtocolExpert Reference Series of White Papers Choosing the Right Interior Routing Protocol1-800-COURSES www.globalknowledge.comChoosing the RightInterior Routing ProtocolDenise Donohue, Global Knowledge Instructor, CCIE #9566IntroductionChoosing an IP routing protocol is an important step. The right protocol can make your routingoperate efficiently, and the wrong one can make your life difficult. Each protocol has its ownpros and cons, and works better in some situations than others. In this paper, we explore thestrengths and weakness of RIP, EIGRP, OSPF, and IS-IS, and discuss when it is appropriate touse each. We will evaluate each protocol in terms of five criteria: • Convergence speed • Ease of use • Network topology required • Vendor support • IPv6 supportThis paper also provides configuration tasks and commands for Cisco routers. It includes tipsfor each protocol, as well as suggestions on designing your network to maximize the efficiencyof each protocol. This paper assumes the reader is already familiar with interior routing proto-cols. It contains a short description of each protocol, but does not go in depth on each of itsfeatures or possible configuration commands. A list of good reference material is at the end ofthe paper, for those wishing more information on a particular protocol.Routing Information Protocol (RIP)RIP was one of the first IP routing protocols. It is simple to understand and simple to configure.RIP version 1 sends its advertisements as broadcasts; RIP version 2 sends them as multicas-ts. Both versions advertise their entire routing table every 30 seconds. For both versions, themetric is hop count – with each router counting as a hop. A network with a metric of 16 hops isconsidered unreachable, which limits the diameter of a RIP routing domain.Convergence SpeedRIP is notoriously slow to converge. It is a distance vector protocol, which means that eachrouter advertises only the path it itself is using to reach a particular network. When there is achange in the network topology, each router recalculates its routing table before announcingthe change to its neighbors. If a network has gone down, the router must query its neighborsfor an alternate path to the network, and wait for them to respond. Additionally, RIP employstimers such as the hold-down timer to lessen the chance of a routing loop. These timers, how-ever, also lengthen the amount of time that incorrect information might be propagated throughthe network.Copyright ©2005 Global Knowledge Network, Inc. All rights reserved. Page 2Ease of UseRIP is an easy protocol to use. All that is required is to enable RIP and configure a networkstatement for the router interfaces that will be running RIP. RIP version 1 is a classful routingprotocol, and thus all links within the RIP domain must use the same subnet mask. RIP version2 is classless, and thus supports variable-length subnet masking (VLSM). With either versionof RIP, the network statement lists only the classful network.Network TopologyThe best place to use RIP is in a small network with links of about the same bandwidth sinceits metric does not account for differences in bandwidth. The more stable the network, the bet-ter RIP performs. RIPv1 is best used on links with only RIP devices, since its advertisementsare sent as broadcasts. If it were used on a LAN link with hosts as well as a neighbor router onthe link, the hosts would be interrupted every 30 seconds by RIP broadcasts. This is not aproblem with RIPv2, since it sends its advertisements to the multicast address of 224.0.0.9.Only devices listening for that multicast address would be affected.When using RIPv1, the same subnet mask must be used on every subnet of a classful net-work. There must be no discontiguous subnets. RIPv2 can handle networks with VLSM, sinceyou can disable auto-summarization.Vendor SupportSince RIP is such a well-known protocol, it is very widely supported. All Cisco routers supportit, as well as firewalls, Microsoft Windows operating systems, and Unix-based operating sys-tems. Some networks must run RIP in order to support a Unix computer. If that is the case inyour network, consider sectioning off that part of the network, confining the RIP portion of thenetwork to as few devices as possible. Run a more sophisticated protocol in the rest of thenetwork, and redistribute the RIP routes into it. If possible, inject only a default route into theRIP area.IPv6 SupportThere is a version of RIP that supports IPv6, called RIPng (RFC 2080). It is available begin-ning in Cisco IOS version 12.2(8)T9.Tasks and TipsOn a Cisco router, enable RIP under the global configuration mode and then list the classfulnetworks for the interfaces where you want to run RIP. For instance, suppose you have t ...