CCNA3_M3_EIGRP (1130758)
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CCNA – Semester3Module 3EIGRPObjectives• EIGRP Concepts• EIGRP Configuration• Thoubleshooting routing protocolsEIGRP ConceptsEIGRP Overview• Cisco released EIGRP in 1994 as a scalable,improved version of its proprietary distancevector routing protocol, IGRP.• EIGRP improves the convergence propertiesand the operating efficiency significantly overIGRP.EIGRP and IGRP• IGRP and EIGRP are compatible with each other.This compatibility provides seamlessinteroperability with IGRP routers.• EIGRP scales the metric of IGRP by a factor of256.• IGRP has a maximum hop count of 255.
EIGRPhas a maximum hop count limit of 224.EIGRP and IGRP route redistribution• Redistribution, the sharing of routes, is automaticbetween IGRP and EIGRP as long as both processes usethe same autonomous system (AS) number.EIGRP concepts and terminology• EIGRP maintains three tables:– Neighbor table– Topology table– Routing table• There is a set of tables for each protocol thatEIGRP supports.Neighbor Table• Lists adjacent routers (comparable to OSPF adjacencydatabase).• The address and interface of new neighbor is recorded.• Diffusing Update Algorithm (DUAL), which is the EIGRPdistance vector algorithm, is informed of the topologychange and must recalculate the new topology.Topology table• All learned routes to a destination are maintained in thetopology table.• By tracking this information, EIGRP routers can identifyand switch to alternate routes quickly.Routing Table• The EIGRP routing table holds the best routes to adestination retrieved from the topology table.Successor route• A successor is a route selected as the primary route touse to reach a destination.• DUAL identifies this route from the informationcontained in the neighbor and topology tables andplaces it in the routing table.• There can be up to four successor routes for anyparticular route.• These can be of equal or unequal cost and are identifiedas the best loop-free paths to a given destination.Feasible successor• A feasible successor (FS) is a backup route.• These routes are identified at the same time thesuccessors are identified, but they are only keptin the topology table.• Multiple feasible successors for a destinationcan be retained in the topology table although itis not mandatory.Alternative routeAlternative route• Successor route goes down Æ look for an identifiedfeasible successor which must have a lower advertisedcost than the existing successor cost to the destination.• If no feasible successor available Æ place the route inActive status and sends out query packets to allneighbors in order to recompute the current topology.• Identify any new successor or feasible successor routesfrom reply packets.
Then place the route in Passivestatus.External routes• External routes originate outside the EIGRP AS.• Routes learned or redistributed from otherrouting protocols, such as Routing InformationProtocol (RIP), OSPF, and IGRP, are external.• Static routes originating outside the EIGRP ASare external.EIGRP design features•••••Rapid convergenceEfficient use of bandwidthSupport for VLSM and CIDR.Multiple network-layer supportIndependence from routed protocols.EIGRP technologies• EIGRP includes many new technologies, each of whichrepresents an improvement in operating efficiency, speed ofconvergence, or functionality relative to IGRP and otherrouting protocols.– Neighbor discovery and recovery– Reliable Transport Protocol– DUAL finite-state machine algorithm– Protocol-dependent modulesAdjacencies• EIGRP routers establish adjacencies withneighbor routers by using small hello packets.By forming adjacencies, EIGRP routers do thefollowing:– Dynamically learn of new routes that join their network– Identify routers that become either unreachable orinoperable– Rediscover routers that had previously been unreachableExchange Routing tableRTP• Reliable Transport Protocol (RTP) is a transportlayer protocol that can guarantee ordereddelivery of EIGRP packets to all neighbors.• To stay independent of IP, EIGRP uses RTP asits own proprietary transport-layer protocol toguarantee delivery of routing information.DUAL• The centerpiece of EIGRP is the Diffusing UpdateAlgorithm (DUAL), which is the EIGRP route-calculationengine - DUAL finite-state machine (FSM).• FSMs define a set of possible states that something cango through, what events cause those states, and whatevents result from those states.• Designers use FSMs to describe how a device, computerprogram, or routing algorithm will react to a set of inputevents.
The DUAL FSM contains all the logic used tocalculate and compare routes in an EIGRP network.DUAL• Each PDM(Protocol Dependent Modules)is responsiblefor all functions related to its specific routed protocol.The IP-EIGRP module is responsible for the following:– Sending and receiving EIGRP packets that bear IP data– Notifying DUAL of new IP routing information that is received– Maintaining the results of DUAL routing decisions in the IP routingtable– Redistributing routing information that was learned by other IPcapable routing protocolsEIGRP data structure• EIGRP relies on different types of packets tomaintain its various tables and establishcomplex relationships with neighbor routers.The five EIGRP packet types are:–––––HelloAcknowledgmentUpdateQueryReplyHello Packet••••EIGRP relies on hello packets to discover, verify, and rediscoverneighbor routers.EIGRP routers send hellos at a fixed but configurable interval,called the hello interval.
The default hello interval depends on thebandwidth of the interface.On IP networks, EIGRP routers send hellos to the multicast IPaddress 224.0.0.10.Hello packets are always sent unreliably. This means that noacknowledgment is transmitted.EIGRP algorithm• Each topology table identifies the following:– The routing protocol or EIGRP– The lowest cost of the route, which is called FeasibleDistance (FD)– The cost of the route as advertised by the neighboringrouter, which is called Reported Distance (RD)EIGRP algorithmFeasible Successor Route SelectionDUAL ExampleDUAL ExampleDUAL ExampleDUAL ExampleDUAL ExampleEIGRP ConfigurationConfiguring EIGRP• router(config)#router eigrp autonomous-systemnumber• router(config-router)#network network-numberDiscontiguous subnetworks• If there are discontiguous subnetworks autosummarization must be disabled for routing to workproperly.
To turn off auto-summarization, use thefollowing command:• router(config-router)#no auto-summaryNo Auto-summarizationManual summary• With EIGRP, a summary address can bemanually configured by configuring a prefixnetwork.• Manual summary routes are configured on aper-interface basis, so the interface that willpropagate the route summary must be selectedfirst.• router(config-if)#ip summary-address eigrpautonomous-system-number ip-address maskadministrative-distanceSummary Example• RTC(config)#router eigrp 2446RTC(config-router)#no auto-summaryRTC(config)#interface serial 0/0RTC(config-if)#ip summary-address eigrp 2446 2.1.0.0255.255.0.0Inter-AS configuration• Static route is prefered for simple connection• Update between ASes may be exchanged byredistributing with default metric:– Redistribute updates:redistribute protocol [AS number | Process-ID]protocol can be any of: connected, static, eigrp, rip, ospf, bgp …– Define default metric:default-metric {metric-string}metric-string can be single as cost in RIP or can be compositive as bandwidth, delay,reliability, loading, mtu in EIGRPVerifying basic EIGRPVerifying basic EIGRPTroubleshooting routing protocolsTroubleshooting RIP configuration• If the RIP routes are not being advertised, check thefollowing:– Layer 1 or Layer 2 connectivity issues exist.– VLSM subnetting is configured.
VLSM subnetting cannot be usedwith RIP v1.– Mismatched RIP v1 and RIP v2 routing configurations exist.– Network statements are missing or incorrectly assigned.– The outgoing interface is down.– The advertised network interface is down.Troubleshooting EIGRP configuration• Some possible reasons why EIGRP may not be workingcorrectly are:––––––Layer 1 or Layer 2 connectivity issues exist.Autonomous system numbers on EIGRP routers are mismatched.The link may be congested or down.The outgoing interface is down.The advertised network interface is down.Auto-summarization is enabled on routers with discontiguoussubnets.– Use no auto-summary to disable automatic network summarizationTroubleshooting OSPF configuration• If a router configured for OSPF routing is not seeing anOSPF neighbor on an attached network, perform thefollowing tasks:– Verify that both routers have been configured with the same IP mask,OSPF hello interval, and OSPF dead interval.– Verify that both neighbors are part of the same area.• debug ip ospf event• debug ip ospf packetSummary• Differences between EIGRP and IGRP• Key concepts, technologies, and data structures ofEIGRP• EIGRP convergence and the basic operation of theDiffusing Update Algorithm, or DUAL• Basic EIGRP configuration• Configuring EIGRP route summarization• Verifying EIGRP operations• The eight-step process for general troubleshooting• Routing protocols troubleshootingLab TopologyCCNA3 – Module3.
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