Quản trị mạng - Eigrp

Choosing the best route After router has received all updates from directly connected neighbors, it can calculate its DUAL 1st metric is calculated for each route 2nd route with lowest metric is designated successor & is placed in routing table 3rd feasible successor is found Criteria for feasible successor: it must have lower reported distance to the destination than the installed route’s feasible distance Feasible routes are maintained in topology table

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EIGRPRouting Protocols and Concepts – Chapter 9ObjectivesDescribe the background and history of Enhanced Interior Gateway Routing Protocol (EIGRP).Examine the basic EIGRP configuration commands and identify their purposes.Calculate the composite metric used by EIGRP.Describe the concepts and operation of DUAL.Describe the uses of additional configuration commands in EIGRP.IntroductionEIGRPRoots of EIGRP: IGRPDeveloped in 1985 to overcome RIPv1’s limited hop countDistance vector routing protocolMetrics used by IGRPBandwidth (used by default)Delay (used by default)ReliabilityLoadDiscontinued support starting with IOS 12.2(13)T & 12.2(R1s4)SEIGRPEIGRP Message FormatEIGRP HeaderData link frame header - contains source and destination MAC addressIP packet header - contains source & destination IP addressEIGRP packet header - contains AS numberType/Length/Field - data portion of EIGRP messageEIGRPEIGRP packet header contains:Opcode fieldAutonomous System numberEIGRP Parameters contain:Weights Hold timeEIGRPTLV: IP internal containsMetric fieldSubnet mask fieldDestination fieldTLV: IP external containsFields used when external routes are imported into EIGRP routing processEIGRPProtocol Dependent Modules (PDM)EIGRP uses PDM to route several different protocols i.e. IP, IPX & AppleTalkPDMs are responsible for the specific routing task for each network layer protocolEIGRPReliable Transport Protocol (RTP)Purpose of RTPUsed by EIGRP to transmit and receive EIGRP packetsCharacteristics of RTPInvolves both reliable & unreliable delivery of EIGRP packetReliable delivery requires acknowledgment from destinationUnreliable delivery does not require an acknowledgement from destinationPackets can be sent UnicastMulticast Using address’s 5 Packet TypesHello packetsUsed to discover & form adjacencies with neighborsEIGRPUpdate packetsUsed to propagate routing informationEIGRPQuery packetsUsed by DUAL for searching for networksCan use Unicast or MulticastReply packetsReply packet Can use Unicast onlyAcknowledgement packetsUsed to acknowledge receipt of update, query & reply packetsEIGRPPurpose of Hello Protocol To discover & establish adjacencies with neighbor routersCharacteristics of hello protocolTime interval for sending hello packetMost networks it is every 5 secondsMultipoint non broadcast multi- access networksUnicast every 60 secondsHoldtimeThis is the maximum time router should wait before declaring a neighbor downDefault holdtime3 times hello intervalEIGRPEIGRP Bounded UpdatesEIGRP only sends update when there is a change in route statusPartial updateA partial update includes only the route information that has changed – the whole routing table is NOT sentBounded updateWhen a route changes, only those devices that are impacted will be notified of the changeEIGRP’s use of partial bounded updates minimizes use of bandwidthEIGRPDiffusing Update Algorithm (DUAL)PurposeEIGRP’s primary method for preventing routing loopsAdvantage of using DUALProvides for fast convergence time by keeping a list of loop-free backup routesEIGRPAdministrative Distance (AD)Defined as the trustworthiness of the source routeEIGRP default administrative distancesSummary routes = 5Internal routes = 90Imported routes = 170EIGRPAuthenticationEIGRP canEncrypt routing informationAuthenticate routing informationEIGRPNetwork TopologyTopology used is the same as previous chapters with the addition of an ISP routerEIGRPEIGRP will automatically summarize routes at classful boundariesBasic EIGRP Configuration Autonomous System (AS) & Process IDsThis is a collection of networks under the control of a single authority (reference RFC 1930)AS Numbers are assigned by IANAEntities needing AS numbersISPInternet Backbone prodiersInstitutions connecting to other institutions using AS numbersBasic EIGRP ConfigurationEIGRP autonomous system number actually functions as a process IDProcess ID represents an instance of the routing protocol running on a routerExampleRouter(config)#router eigrp autonomous-systemBasic EIGRP ConfigurationThe router eigrp commandThe global command that enables eigrp isrouter eigrp autonomous-system All routers in the EIGRP routing domain must use the same process ID number (autonomous-system number)Basic EIGRP ConfigurationThe Network CommandFunctions of the network commandEnables interfaces to transmit & receive EIGRP updatesIncludes network or subnet in EIGRP updatesExampleRouter(config-router)#network network-addressBasic EIGRP ConfigurationThe network Command with a Wildcard MaskThis option is used when you want to configure EIGRP to advertise specific subnetsExampleRouter(config-router)#network network-address [wildcard-mask] Basic EIGRP ConfigurationVerifying EIGRPEIGRP routers must establish adjacencies with their neighbors before any updates can be sent or receivedCommand used to view neighbor table and verify that EIGRP has established adjacencies with neighbors isshow ip eigrp neighborsEIGRPThe show ip protocols command is also used to verify that EIGRP is enabledBasic EIGRP ConfigurationExamining the Routing TableThe show ip route command is also used to verify EIGRPEIGRP routes are denoted in a routing table by the letter “D”By default , EIGRP automatically summarizes routes at major network boundaryBasic EIGRP ConfigurationIntroducing the Null0 Summary RouteNull0 is not a physical interfaceIn the routing table summary routes are sourced from Null0Reason: routes are used for advertisement purposesEIGRP will automatically include a null0 summary route as child route when 2 conditions are metAt least one subnet is learned via EIGRPAutomatic summarization is enabledBasic EIGRP ConfigurationR3’s routing table shows that the network is automatically summarized by R1 & R3EIGRP Metric CalculationEIGRP Composite Metric & the K ValuesEIGRP uses the following values in its composite metricBandwidth, delay, reliability, and loadThe composite metric used by EIGRP Formula used has values K1 K5K1 & K3 = 1all other K values = 0 EIGRP Metric CalculationUse the sh ip protocols command to verify the K valuesEIGRP Metric CalculationEIGRP MetricsUse the show interfaces command to view metricsEIGRP MetricsBandwidth – EIGRP uses a static bandwidth to calculate metricMost serial interfaces use a default bandwidth value of 1.544Mbos (T1)EIGRP Metric CalculationEIGRP MetricsDelay is the defined as the measure of time it takes for a packet to traverse a routeIt is a static value based on link type to which interface is connectedEIGRP Metric CalculationReliability (not a default EIGRP metric)A measure of the likelihood that a link will failMeasure dynamically & expressed as a fraction of 255 the higher the fraction the better the reliabilityLoad (not a default EIGRP metric)A number that reflects how much traffic is using a linkNumber is determined dynamically and is expressed as a fraction of 255The lower the fraction the less the load on the linkEIGRP Metric CalculationUsing the Bandwidth CommandModifying the interface bandwidthUse the bandwidth commandExampleRouter(config-if)#bandwidth kilobitsVerifying bandwidth Use the show interface commandNote – bandwidth command does not change the link’s physical bandwidthEIGRP Metric CalculationThe EIGRP metric can be determined by examining the bandwidth delayEIGRP Metric CalculationEIGRP uses the lowest bandwidth (BW)in its metric calculationCalculated BW = reference BW / lowest BW(kbps)Delay – EIGRP uses the cumulative sum of all outgoing interfacesCalculated Delay = the sum of outgoing interface delaysEIGRP Metric = calculated BW + calculated delayEIGRP Metric CalculationDUAL ConceptsThe Diffusing Update Algorithm (DUAL) is used to prevent loopingDUAL ConceptsSuccessor The best least cost route to a destination found in the routing tableFeasible distanceThe lowest calculated metric along a path to a destination networkDUAL ConceptsFeasible Successors, Feasibility Condition & Reported DistanceFeasible SuccessorThis is a loop free backup route to same destination as successor routeDUAL ConceptsReported distance (RD)The metric that a router reports to a neighbor about its own cost to that networkFeasible Successors, Feasibility Condition & Reported DistanceDUAL ConceptsFeasibility Condition (FC)Met when a neighbor’s RD is less than the local router’s FD to the same destination networkDUAL ConceptsTopology Table: Successor & Feasible SuccessorEIGRP Topology tableViewed using the show ip eigrp topology commandContents of table include: all successor routes all feasible successor routesDUAL ConceptsEIGRP Topology Table dissectedDUAL ConceptsTopology Table: No Feasible SuccessorA feasible successor may not be present because the feasibility condition may not be metIn other words, the reported distance of the neighbor is greater than or equal to the current feasible distanceDUAL ConceptsFinite Sate Machine (FSM)An abstract machine that defines a set of possible states something can go through, what event causes those states and what events result form those statesFSMs are used to describe how a device, computer program, or routing algorithm will react to a set of input eventsDUAL ConceptsDUAL FSMSelects a best loop-free path to a destinationSelects alternate routes by using information in EIGRP tablesDUAL ConceptsFinite State Machines (FSM)To examine output from EIGRP’s finite state machine us the debug eigrp fsm commandMore EIGRP ConfigurationsThe Null0 Summary RouteBy default, EIGRP uses the Null0 interface to discard any packets that match the parent route but do not match any of the child routesEIGRP automatically includes a null0 summary route as a child route whenever both of the following conditions existOne or subnets exists that was learned via EIGRPAutomatic summarization is enabledMore EIGRP ConfigurationsThe Null0 Summary RouteMore EIGRP ConfigurationsDisabling Automatic SummarizationThe auto-summary command permits EIGRP to automatically summarize at major network boundariesThe no auto-summary command is used to disable automatic summarizationThis causes all EIGRP neighbors to send updates that will not be automatically summarizedThis will cause changes to appear in both routing tables topology tablesMore EIGRP ConfigurationsManual SummarizationManual summarization can include supernetsReason: EIGRP is a classless routing protocol & include subnet mask in updateCommand used to configure manual summarization Router(config-if)#ip summary-address eigrp  as-number network-address subnet-maskMore EIGRP ConfigurationsConfiguring a summary route in EIGRPMore EIGRP ConfigurationsEIGRP Default Routes“Quad zero” static default routeCan be used with any currently supported routing protocolIs usually configured on a router that is connected a network outside the EIGRP domainEIGRP & the “Quad zero” static default routeRequires the use of the redistribute static command to disseminate default route in EIGRP updatesMore EIGRP ConfigurationsFine-Tuning EIGRPEIGRP bandwidth utilizationBy default, EIGRP uses only up to 50% of interface bandwidth for EIGRP informationThe command to change the percentage of bandwidth used by EIGRP isRouter(config-if)#ip bandwidth-percent eigrp as-number percentMore EIGRP ConfigurationsConfiguring Hello Intervals and Hold TimesHello intervals and hold times are configurable on a per-interface basisThe command to configure hello interval isRouter(config-if)#ip hello-interval eigrp as-number secondsChanging the hello interval also requires changing the hold time to a value greater than or equal to the hello intervalThe command to configure hold time value isRouter(config-if)#ip hold-time eigrp as-number secondsSummaryBackground & HistoryEIGRP is a derivative of IGRPEIGRP is a Cisco proprietary distance vector routing protocol released in 1994EIGRP terms and characteristicsEIGPR uses RTP to transmit & receive EIGRP packetsEIGRP has 5 packet type:Hello packetsUpdate packetsAcknowledgement packetsQuery packetsReply packetsSupports VLSM & CIDRSummaryEIGRP terms and characteristicsEIGRP uses a hello protocolPurpose of hello protocol is to discover & establish adjacenciesEIGRP routing updatesAperiodicPartial and boundedFast convergenceSummaryEIGRP commandsThe following commands are used for EIGRP configurationRtrA(config)#router eigrp [autonomous-system #]RtrA(config-router)#network network-numberThe following commands can be used to verify EIGRPShow ip protocolsShow ip eigrp neighborsShow ip routeSummaryEIGRP metrics includeBandwidth (default)Delay (default)ReliabilityLoadSummaryDUALPurpose of DUALTo prevent routing loopsSuccessorPrimary route to a destinationFeasible successorBackup route to a destinationFeasible distanceLowest calculated metric to a destinationReported distanceThe distance towards a destination as advertised by an upstream neighborSummaryChoosing the best routeAfter router has received all updates from directly connected neighbors, it can calculate its DUAL1st metric is calculated for each route2nd route with lowest metric is designated successor & is placed in routing table3rd feasible successor is found Criteria for feasible successor: it must have lower reported distance to the destination than the installed route’s feasible distanceFeasible routes are maintained in topology tableSummaryAutomatic summarizationOn by defaultSummarizes routes on classful boundarySummarization can be disabled using the following commandRtrA(config-if)#no auto-summary

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