6 Link-State routing เริ่มต้นตรวจสอบสถานะของลิงค์ แต่ละโหนดเก็บ link states ของตัวเองกระจาย link states ให้โหนดอื่นภายในพื่นที่ (flooding)คำนวน shortest path ของจากโหนดตัวเองไปยังโหนดอื่น ๆ โดยใช้Dijktsta ‘a algorithm
7 เปรียบเทียบ Distance-vector และ Link state ข้อดีใช้หน่วยความจำน้อยการคำนวณไม่ซับซ้อนข้อเสียSlow convergenceสามารถเกิด routing loopข้อดีFast convergenceข้อเสียใช้หน่วยความจำมากการคำนวณซับซ้อนกว่า
12 ถ้า link 1-5 มีปัญหา Node 2 ไม่สามารถส่งข้อมูลไปยัง Network A
13 EIGRP Improved version of IGRP Backwards compatible with IGRP Improved convergenceSends updates like a link state routing protocolSupports VLSM/CIDRSupports many layer 3 routed protocols (not just IP)Routing protocol designed by CiscoCombines best features of link-state and distance vector routing protocolsCompatible with IGRPTwo major versionsVersion 0Version 1
14 Advantages of EIGRP Rapid convergence Low routing update traffic Support for multiple protocolsSupport for VLSMs and classless routingSupport for route summarization along arbitrary boundaries
15 EIGRP Features Hellos sent every 5 secs Neighbour table Topology table DUAL takes information in neighbour & topology table and calculates best routes (‘successors’) and adds them to the Routing Table‘Feasible successors’ are alternative, backup routes
16 Hybrid Routing Protocol Features Hybrid of link-state and distance vector routing protocolsLearns routes from connected interfaces or their neighborsDoes not need to know entire network topologyDoes not require much memory or CPU to calculate routing tablesSaves bandwidth by sending routing updates only to routers that need the information
17 EIGRP Strategies to Avoid Routing Loops Uses Diffusing Update Algorithm (DUAL)Routers store back-up routes by using topology tableTopology table contains only routes advertised by neighboring routersComparison of EIGRP with RIP and OSPFRIP is pure distance vector routing protocolOSPF is pure link-state routing protocolการพิสูจน์ว่าไม่มี Loop สามารถอ่านเพิ่มเติมJ.J.Garcia-Luna-Aceves, “Loop-Free Routing Using Diffusing computations,” IEE/ACM networking, Vol. 1, No. 1, February 1993.
18 EIGRP Operation Uses hello packets to identify neighbors Uses reliable transport to exchange routing informationStores information about neighbors and their routesUses this information to build routing tables
19 EIGRP Technologies Hellos multicast every 5 seconds to 188.8.131.52 Holdtime (route dead) - 3 x hello intervalRTP used as a reliable transport protocol to remain protocol independentSequence numbers used on replies/acknowledgements to hellos – unicast NOT multicastMulticast update packets sent when topology changes
20 Transmission of EIGRP Packets On IP network, EIGRP uses IP packetsIdentified as protocol 88 in the IP headerReliable Transport Protocol (RTP) has sequence number in each packetRequires explicit acknowledgement for each packet sent reliablyRTP builds transmission list for each neighbor and retransmits up to 16 times or until hold time expires
21 Multicast Packets with EIGRP Multicast packet to all neighbors is more efficient than multiple hello packets requiring acknowledgementRTP flag in packet indicates no acknowledgement is necessaryRTP flag also used in packets carrying routing updates
22 Five Types of EIGRP Packets Hello packetsUpdate packetsACK packetsQuery packetsReply packets
23 EIGRP packetsThe destination IP address in EIGRP depends on the packet type--some packets are sent as multicast (with an address of ) and others are sent as unicastThe source IP address is the IP address of the interface from which the packet is issued.Following the IP header is an EIGRP header.
24 An EIGRP header The fields following the EIGRP header depend on the opcode field.
25 IP internal route updates -Type field of 0x0102-The next hop identifies the router to send packets destined for destination-The prefix length field signifies the subnet mask
27 Building and Maintaining Neighbor Relationships Hello packets discover and maintain relationships with neighboring routersPackets sent at hello intervalDefault is 5 seconds for fast interfaces and up to 60 seconds for slower linksDefault hold time is three times the hello interval but may be up to 180 seconds for slower linksHello interval and hold time may be configured independently
28 Exchanging Neighbor Information in Hello Packets To become neighbors, routers must shareCommon subnetSame Autonomous System numberSame constants to calculate EIGRP’s metric
29 Neighbor TableNeighbor table contains information about router’s neighbors including:Neighbor address and interfaceHold time and UptimeSmooth round trip timer (SRTT)Retransmission timeout (RTO)Handle (H)Queue countSequence number
30 Building the Topology Table with Update Packets Topology table consists of all the routes each neighbor advertisesIncludes metrics advertised by neighbors for routesIncludes metric the router itself uses to forward packets to those destinationsAdds metric to get to neighbor to metric advertised by neighbor to destinations
31 Building and Maintaining Routing Tables Building routing tables for first timeWhen router becomes part of EIGRP network, it sends out hello packets on all interfacesNeighbor replies with update packets containing Init bit to indicate a new neighbor relationship.New router acknowledges each update packet and uses information in packets to builds its topology tableNew router then sends update packets to all neighborsEach neighbor replies with an ACKSee the Table in the next slide
33 Building Routing Tables Uses DUAL algorithm to select primary and back-up routes for each destinationIncludes these routes in its topology tableSupports internal, external, and summary routesAdds best route into routing table as successor route
35 EIGRP Metric Five variables used to calculate metric BandwidthDelayReliabilityLoadMaximum transmission units (MTU)Uses constants, called K-values, to calculate final metricFinal metric value multiplied by 256 results in a 32-bit metric value
36 Default K-valuesbandwidth (kbps)Delay (tens of microsecond)
37 ตัวอย่างการคำนวณ Metric B= bandwidth (kbps)d= Delay (tens of microsecond)
38 ตัวอย่างการคำนวณ metric Metric=[K1*bandwidth+(K2*bandwidth)/(256-load)+K3*delay)]*[K5/(Reliability+K4)]K1=1, K2=0, K3=1, K4=0, K5=0Metric =[bandwidth + delay]No floating point, Round downRouter 1 to Network AVia router 4(10,000,000/ )*256=( )*256=Via router 3(10,000,000/ )*256=( )*256=79325*256=Router 1 to Network A: Via router 3
39 Maintaining Routing Tables with the DUAL Algorithm DUAL is a finite state machineEach state is loop-free routing tableDUAL watches for topology changesSelecting best path with DUAL AlgorithmAdvertised distance (AD) or lowest cost is advertised to neighborsFeasible distance (DF) is total metric to destinationSuccessor or lower cost loop-free path is added to routing tableCurrent successor is primary route to any destination
40 Route States (two states) Active - recomputation is being performedPassive - no recomputation going onIf feasible successors are always available, a destination never goes into the active state.Recomputation occurs when no feasible successor route existsIf a neighbor who is the only feasible successor to a destination goes down, all of the neighbor's routes enter the active state and trigger route recomputation.Recomputation ProcessSend a query packet to all neighboring routersNeighbor sendsa reply that it has a feasible successor, ora query packet to indicate it is partcipating in the recomputationRoutes in the active state cannot have their routing table information changedOnce all neighbors have replied the topology table entry for the destination returns to the pasive state and the router may then select a feasible successor.
41 Selecting Feasible Successors Feasible successor is next best route to destinationEIGRP may keep more than one feasible successor in its topology tableNext hop router must have advertised distance to destination less than feasible distance of route of current successorHelps prevent routing loops
42 Failure of the Primary Route DUAL algorithm looks at each feasible successor in topology databaseChooses one with lowest metric; does not have to recalculate itIf no feasible successor exists, router queries neighbors in query range with split horizon rule to find new routeNew route goes from passive to active state and must be recalculatedIf no response to query packet within time limit, router enters stuck-in-active (SIA) state
43 Topology Change on an EIGRP Network When router joins network, it builds routing table, using information from neighbors.If more than one possible path exists to a network, router chooses path with best feasible distancesIf serial link goes down, router must find a new route to destination network
47 Using EIGRP on Very Large Networks Use special care to minimize routing problems and convergence timeEIGRP scalability is affected by variablesNumber of routers involved in network changeAmount of routing information exchanged by EIGRP neighborsNumber of hops information travels to reach all affected routersNumber of redundant paths on network
48 Restrict and Eliminate Queries Lost reply packets result in serious convergence problemsHeavy CPU or memory usage on router causes problemsThe larger the query scope in an Autonomous System, the more likely routers are to end up in SIA modeSize of query depends on number of neighbors and number of paths a query might take
49 Restricting Query Scope Segment a network into multiple Autonomous SystemsMay not solve problemUse route summarizationSummary routes must be placed appropriately
50 Restricting Queries with Multiple EIGRP Autonomous Systems
51 Route TaggingInternal routes come from neighbors with the same (E)IGRP AS number or from directly attached interfaces over which IGRP or EIGRP runs.External routes come from other routing protocols or from static routes and are tagged with the following information:Router ID of the router that distributed the routeAS number of the destinationConfigurable administrator tagID of the external protocolMetric from the external protocolBit flags for default routing
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