Bài giảng Mạng máy tính nâng cao - Chapter 09: EIGRP: of Enhanced Interior Gateway Routing Protocol

Chapter 09EIGRP: of Enhanced Interior Gateway Routing Protocol MẠNG MÁY TÍNH NÂNG CAOObjectives Describe 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.Introduction IntroductionEIGRP Message FormatThe data portion of an EIGRP message is encapsulated in a packet. This data field is called Type/Length/Value or TLVData 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 messageEIGRP Message FormatEIGRP Message FormatProtocol 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 protocolReliable Transport Protocol (RTP) Reliable Transport Protocol (RTP) is the protocol used by EIGRP for the delivery and reception of EIGRP packets. EIGRP was designed as a Network layer independent routing protocol; therefore, it cannot use the services of UDP or TCP because IPX and Appletalk do not use protocols from the TCP/IP protocol suite. The figure shows conceptually how RTP operates. Reliable Transport Protocol (RTP)Characteristics of RTP Involves both reliable and unreliable delivery of EIGRP packetReliable delivery requires acknowledgment from destinationUnreliable delivery does not require an acknowledgement from destinationPackets can be sent UnicastMulticast: Using address 224.0.0.10EIGRP Packet TypesEIGRP’s 5 Packet TypesHello packetsUsed to discover & form adjacencies with neighborsEIGRP Packet TypesUpdate packetsUsed to propagate routing informationEIGRP Packet TypesQuery 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 packetsHello ProtocolPurpose 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 networks: Unicast every 60 secondsHoldtimeThis is the maximum time router should wait before declaring a neighbor downDefault holdtime3 times hello intervalEIGRP UpdateEIGRP 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 bandwidthDiffusing 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 routesAdministrative Distance (AD)Administrative Distance (AD): Defined as the trustworthiness of the source routeEIGRP default administrative distancesSummary routes = 5Internal routes = 90Imported routes = 170AuthenticationEIGRP canEncrypt routing informationAuthenticate routing informationrouters will only accept routing information from other routers that have been configured with the same password or authentication information. Note: Authentication does not encrypt the router's routing table.Network TopologyA loopback interface can be used to represent an interface on a router that does not have any actual connection to a physical link on the network. Loopback addresses can be verified with the ping command and included in routing updates.Network TopologyBasic 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 providersInstitutions connecting to other institutions using AS numbersBasic EIGRP ConfigurationBasic EIGRP Configuration Basic EIGRP Configuration The 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 Configuration The Network CommandFunctions of the network commandEnables interfaces to transmit & receive EIGRP updatesIncludes network or subnet in EIGRP updatesExample:Router(config-router)#network network-addressBasic EIGRP Configuration The 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] Verifying 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 is show ip eigrp neighborsVerifying EIGRPThe show ip protocols command is also used to verify that EIGRP is enabledVerifying EIGRPExamining 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 boundaryIntroducing 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 enabledThe null0 summary route is removed when automatic summary is disabled.Introducing the Null0 Summary RouteVerifying EIGRPR3’s routing table shows that the 172.16.0.0/16 network is automatically summarized by R1 & R2EIGRP Metric Calculation EIGRP Composite Metric & the K ValuesEIGRP uses the following values in its composite metric: Bandwidth, delay, reliability, and loadThe composite metric used by EIGRPFormula used has values K1 K5K1 & K3 = 1all other K values = 0EIGRP Metric CalculationUse the show ip protocols command to verify the K valuesEIGRP Metric CalculationUse the show interfaces command to view metricsBandwidth – EIGRP uses a static bandwidth to calculate metricMost serial interfaces use a default bandwidth value of 1.544Mbps (T1) The bandwidth is displayed in Kbit (kilobits)EIGRP Metric Calculation Delay 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 connected EIGRP Metric Calculation Reliability (not a default EIGRP metric)A measure of the probability that the 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 CalculationEIGRP Metric Calculation The EIGRP metric can be determined by examining the bandwidth, delayEIGRP Metric Calculation EIGRP uses the lowest bandwidth (BW)in its metric calculation Calculated BW = reference BW / lowest BW(kbps)Delay – EIGRP uses the cumulative sum of all outgoing interfaces Calculated Delay = the sum of outgoing interface delaysEIGRP Metric = calculated BW + calculated delayEIGRP Metric Calculation DUAL Concepts The Diffusing Update Algorithm (DUAL) is used to prevent loopingDUAL ConceptsSuccessor A successor is a neighboring router that is used for packet forwarding and is the least-cost route to a destination found in the routing tableFeasible distanceThe lowest calculated metric along a path to a destination networkDUAL Concepts Feasible Successor This 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 networkDUAL ConceptsFeasibility Condition (FC)Met when a neighbor’s RD is less than the local router’s FD to the same destination networkDUAL ConceptsDUAL ConceptsDUAL Concepts DUAL ConceptsFinite State 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 Configurations The 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 ConfigurationsMore EIGRP Configurations Disabling 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 Configurations Manual 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 ConfigurationsMore EIGRP ConfigurationsFine-Tuning EIGRP: EIGRP 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 percent More EIGRP Configurations