Quản trị mạng - Chapter 9: Eigrp

Describe the background and history of EIGRP • Describe the features and operation of EIGRP • Examine the basic EIGRP configuration commands and identity 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

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1Chapter 9: EIGRP CCNA Exploration version 4.0 Học viện mạng Bach Khoa - Website: www.bkacad.com 2 Objectives • 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. Học viện mạng Bach Khoa - Website: www.bkacad.com 3 Introduction to EIGRP Học viện mạng Bach Khoa - Website: www.bkacad.com 4 EIGRP • The main purpose in Cisco's development of EIGRP was to create a classless version of IGRP. • EIGRP includes several features that are not commonly found in other distance vector routing protocols like RIP (RIPv1 and RIPv2) and IGRP. • These features include: 1. Reliable Transport Protocol (RTP) 2. Bounded Updates 3. Diffusing Update Algorithm (DUAL) 4. Establishing Adjacencies 5. Neighbor and Topology Tables • Although EIGRP may act like a link-state routing protocol, it is still a distance vector routing protocol. Học viện mạng Bach Khoa - Website: www.bkacad.com 5 EIGRP • Roots of EIGRP: IGRP – Developed in 1985 to overcome RIPv1’s limited hop count – Distance vector routing protocol – Metrics used by IGRP  bandwidth (used by default)  delay (used by default)  reliability  load – Discontinued support starting with IOS 12.2(13)T & 12.2(R1s4)S Học viện mạng Bach Khoa - Website: www.bkacad.com 6 IGRP to EIGRP Enhanced Distance Vector Routing Protocol: EIGRP • Uses the Diffusing Update Algorithm (DUAL) • Does not age out routing entries nor uses periodic updates. • Maintains a topology table separate from the routing table, which includes the best path and any loop- free backup paths. • When a route becomes unavailable, DUAL will use a backup path if one exists in the topology table. • Faster convergence due to the absence of holddown timers and a system of coordinated route calculations. Traditional Distance Vector Routing Protocols • Use the Bellman-Ford or Ford-Fulkerson algorithm. • Age out routing entries and uses periodic updates. • Keep track of only the best routes; the best path to a destination network. • When a route becomes unavailable, the router must wait for a new routing update. • Slower convergence due to holddown timers. Học viện mạng Bach Khoa - Website: www.bkacad.com 7 EIGRP Capabilities and Attributes Học viện mạng Bach Khoa - Website: www.bkacad.com 8 • The data portion of an EIGRP message is encapsulated in a packet. This data field is called Type/Length/Value or TLV. EIGRP Message Format Học viện mạng Bach Khoa - Website: www.bkacad.com 9 • The Autonomous System (AS) Number specifies the EIGRP routing process. – Unlike RIP, Cisco routers can run multiple instances of EIGRP. – The AS number is used to track multiple instances of EIGRP. • EIGRP Parameters contains – Weights – Hold time EIGRP Message Format Học viện mạng Bach Khoa - Website: www.bkacad.com 10 • TLV: IP internal contains – Metric field – Subnet mask field – Destination field • TLV: IP external contains – Fields used when external routes are imported into EIGRP routing process EIGRP Message Format Học viện mạng Bach Khoa - Website: www.bkacad.com 11 Protocol Dependent Modules (PDM) Học viện mạng Bach Khoa - Website: www.bkacad.com 12 RTP and EIGRP Packet Types Học viện mạng Bach Khoa - Website: www.bkacad.com 13 • Purpose of RTP: to transmit and receive EIGRP packets • Characteristics of RTP – Involves both reliable & unreliable delivery of EIGRP packet  Reliable delivery requires acknowledgment from destination  Unreliable delivery does not require an acknowledgement from destination – Packets can be sent Unicast Multicast : Using address 224.0.0.10 RTP and EIGRP Packet Types Học viện mạng Bach Khoa - Website: www.bkacad.com 14 RTP and EIGRP Packet Types Học viện mạng Bach Khoa - Website: www.bkacad.com 15 RTP and EIGRP Packet Types Học viện mạng Bach Khoa - Website: www.bkacad.com 16 Hello Protocol Học viện mạng Bach Khoa - Website: www.bkacad.com 17 RTP and EIGRP Packet Types Học viện mạng Bach Khoa - Website: www.bkacad.com 18 RTP and EIGRP Packet Types • Update packets –Used to propagate routing information –Update packets are sent as a multicast when required by multiple routers, or as a unicast when required by only a single router. • Acknowledgement packets –Used to acknowledge receipt of update, query & reply packets –EIGRP acknowledgement packets are always sent as an unreliable unicast. Học viện mạng Bach Khoa - Website: www.bkacad.com 19 RTP and EIGRP Packet Types Học viện mạng Bach Khoa - Website: www.bkacad.com 20 RTP and EIGRP Packet Types Query & Reply packets Used by DUAL for searching for networks Query packets: can use: Unicast Multicast Reply packet: use only unicast Học viện mạng Bach Khoa - Website: www.bkacad.com 21 • EIGRP’s use of partial bounded updates minimizes use of bandwidth EIGRP Bounded Updates Học viện mạng Bach Khoa - Website: www.bkacad.com 22 Diffusing Update Algorithm (DUAL) –Purpose: •EIGRP’s primary method for preventing routing loops –Advantage: •Provides for fast convergence time by keeping a list of loop- free backup routes DUAL: An Introduction Học viện mạng Bach Khoa - Website: www.bkacad.com 23 Administrative Distance Học viện mạng Bach Khoa - Website: www.bkacad.com 24 • Note: Authentication does not encrypt the router's routing table Authentication Học viện mạng Bach Khoa - Website: www.bkacad.com 25 Basic EIGRP Configuration Học viện mạng Bach Khoa - Website: www.bkacad.com 26 Network Topology • Topology used is the same as previous chapters with the addition of an ISP router EIGRP Network Topology Học viện mạng Bach Khoa - Website: www.bkacad.com 27 • An autonomous system (AS) is a collection of networks under the administrative control of a single entity that presents a common routing policy to the Internet.(reference RFC 1930) • AS Numbers are assigned by IANA • Entities needing AS numbers  ISP  Internet Backbone providers  Institutions connecting to other institutions using AS numbers Autonomous System and Process IDs Học viện mạng Bach Khoa - Website: www.bkacad.com 28 Autonomous System and Process IDs Học viện mạng Bach Khoa - Website: www.bkacad.com 29 • EIGRP autonomous system number actually functions as a process ID • Process ID represents an instance of the routing protocol running on a router Autonomous System and Process IDs Học viện mạng Bach Khoa - Website: www.bkacad.com 30 The router eigrp Command • All routers in the EIGRP routing domain must use the same process ID number (autonomous-system number) Học viện mạng Bach Khoa - Website: www.bkacad.com 31 • Functions of the network command – Enables interfaces to transmit & receive EIGRP updates – Includes network or subnet in EIGRP updates The network Command Directly connected classful address Học viện mạng Bach Khoa - Website: www.bkacad.com 32 The network Command Router(config-router)#network network-address [wildcard-mask] • This option is used when you want to configure EIGRP to advertise specific subnets Học viện mạng Bach Khoa - Website: www.bkacad.com 33 • EIGRP routers must establish adjacencies with their neighbors before any updates can be sent or received • Command used to view neighbor table and verify that EIGRP has established adjacencies with neighbors is – show ip eigrp neighbors Verifying EIGRP Học viện mạng Bach Khoa - Website: www.bkacad.com 34 • If any packet is reliably multicast and an ACK is not received from a neighbor, the packet will be retransmitted as a unicast to that unresponding neighbor. • If an ACK is not received after 16 of these unicast retransmissions, the neighbor will be declared dead. • The time to wait for an ACK before switching from multicast to unicast is specified by the multicast flow timer. • Smooth Round Trip Timer (SRTT): the average elapsed time, measured in milliseconds, between the transmission of a packet to the neighbor and the receipt of an acknowledgment. • This timer is used to determine the retransmit interval (RTO) • The RTO is the time, in milliseconds, that the router will wait for an acknowledgment of a unicast packet sent after a multicast has failed. • Hold Time The interval to wait without receiving anything from a neighbor before considering the link unavailable. • Originally, the expected packet was a hello packet, but in current Cisco IOS software releases, any EIGRP packets received after the first hello will reset the timer. • The formulas for calculating the exact values of the SRTT, the RTO, and the multicast flow timer are proprietary. Extra: Neighbor Table Học viện mạng Bach Khoa - Website: www.bkacad.com 35 RouterC#show ip eigrp neighbors IP-EIGRP neighbors for process 44 H Address Interface Hold Uptime SRTT RTO Q Seq (sec) (ms) Cnt Num 0 192.168.0.1 Se0 11 00:03:09 1138 5000 0 6 1 192.168.1.2 Et0 12 00:34:46 4 200 0 4 • Neighbor address: The network-layer address of the neighbor router(s). • Queue count: The number of packets waiting in queue to be sent. If this value is constantly higher than zero, then there may be a congestion problem at the router. A zero means that there are no EIGRP packets in the queue. • Sequence Number: The number of last packet that is received from that neighbor. EIGRP uses this field to acknowledge a neighbor’s transmission and to identify packets that are out of sequence. Extra: Neighbor Table Học viện mạng Bach Khoa - Website: www.bkacad.com 36 • The show ip protocols command is used to verify that EIGRP is enabled Verifying EIGRP Học viện mạng Bach Khoa - Website: www.bkacad.com 37 Examining the Routing Table Học viện mạng Bach Khoa - Website: www.bkacad.com 38 • By default , EIGRP automatically summarizes routes at major network boundary Examining the Routing Table Học viện mạng Bach Khoa - Website: www.bkacad.com 39 Introducting the Null0 Summary Route Học viện mạng Bach Khoa - Website: www.bkacad.com 40 • Null0 is not a physical interface • In the routing table summary routes are sourced from Null0 – Reason: routes are used for advertisement purposes • EIGRP will automatically include a null0 summary route as child route when 2 conditions are met: 1. At least one subnet is learned via EIGRP 2. Automatic summarization is enabled Introducting the Null0 Summary Route Học viện mạng Bach Khoa - Website: www.bkacad.com 41 Examining the Routing Table auto-summary Học viện mạng Bach Khoa - Website: www.bkacad.com 42 EIGRP Metric Calculation Học viện mạng Bach Khoa - Website: www.bkacad.com 43 EIGRP Metric Calculation Học viện mạng Bach Khoa - Website: www.bkacad.com 44 • Use the show ip protocols command to verify the K values EIGRP Composite Metric and the K Values Học viện mạng Bach Khoa - Website: www.bkacad.com 45 • Use the show interfaces command to view metrics • Bandwidth – EIGRP uses a static bandwidth to calculate metric • Most serial interfaces use a default bandwidth value of 1.544Mbos (T1) EIGRP Metric Calculation Học viện mạng Bach Khoa - Website: www.bkacad.com 46 EIGRP Metric Calculation Delay • Delay is the defined as the measure of time it takes for a packet to traverse a route • it is a static value based on link type to which interface is connected Học viện mạng Bach Khoa - Website: www.bkacad.com 47 EIGRP Metric Calculation Học viện mạng Bach Khoa - Website: www.bkacad.com 48 • Reliability (not a default EIGRP metric) – A measure of the likelihood that a link will fail – Measure dynamically & expressed as a fraction of 255 the higher the fraction the better the reliability • Load (not a default EIGRP metric) – A number that reflects how much traffic is using a link – Number is determined dynamically and is expressed as a fraction of 255 – The lower the fraction the less the load on the link EIGRP Metric Calculation Học viện mạng Bach Khoa - Website: www.bkacad.com 49 Router(config-if)#bandwidth kilobits • Note – bandwidth command does not change the link’s physical bandwidth EIGRP Metric Calculation Học viện mạng Bach Khoa - Website: www.bkacad.com 50 EIGRP Metric Calculation Học viện mạng Bach Khoa - Website: www.bkacad.com 51 EIGRP Metric Calculation • EIGRP uses the lowest bandwidth (BW) in its metric calculation: Calculated BW = (reference BW / lowest BW(kbps)*256 (reference BW = 107 ) • Delay – EIGRP uses the cumulative sum of all outgoing interfaces: Calculated Delay = (the sum of outgoing interface delays/10)*256 • EIGRP Metric = calculated BW + calculated delay Học viện mạng Bach Khoa - Website: www.bkacad.com 52 EIGRP Metric Calculation • Calculate the metric from R2 to 192.168.1.0/24 Học viện mạng Bach Khoa - Website: www.bkacad.com S0/0 192.168.64.2/30 S0/0 192.168.64.1/30 S0/1 192.168.64.6/30 S0/0 192.168.64.5/30 Fa0/0 192.168.72.1/24 Fa0/0 192.168.1.1/24 Fa0/0 192.168.1.2/24 EIGRP AS 100 Calculated Bandwidth = (10,000,000/bandwidth kbps) * 256 Westasman SanJose1 SanJose2 Bandwidth = 1,657,856 Bandwidth = 25,600 Delay = 512,000 Delay = 2,560 Determining the costs FastEthernet = (10,000,000/100,000) * 256 = 25,600 T1 = (10,000,000/1544) * 256 = 1,657,856 Học viện mạng Bach Khoa - Website: www.bkacad.com S0/0 192.168.64.2/30 S0/0 192.168.64.1/30 S0/1 192.168.64.6/30 S0/0 192.168.64.5/30 Fa0/0 192.168.72.1/24 Fa0/0 192.168.1.1/24 Fa0/0 192.168.1.2/24 EIGRP AS 100 Calculated Delay = (delay/10) * 256 Westasman SanJose1 SanJose2 Bandwidth = 1,657,856 Bandwidth = 25,600 Delay = 512,000 Delay = 2,560 Determining the costs FastEthernet = (100/10) * 256 = 2,560 T1 = (20,000/10) * 256 = 512,000 Học viện mạng Bach Khoa - Website: www.bkacad.com The Routing Table Administrative Distance / MetricSanJose2#show ip route D 192.168.72.0/24 [90/2172416] via 192.168.64.6, 00:28:26, Serial0 Học viện mạng Bach Khoa - Website: www.bkacad.com 56 Diffusing Update Algorithm (DUAL) Học viện mạng Bach Khoa - Website: www.bkacad.com 57 Diffusing Update Algorithm • The design philosophy behind DUAL is that even temporary routing loops are detrimental to the performance of a network. Học viện mạng Bach Khoa - Website: www.bkacad.com 58 • The Diffusing Update Algorithm (DUAL) is used to prevent looping: –Successor –Feasible Distance (FD) –Feasible Successor (FS) –Reported Distance (RD) or Advertised Distance (AD) –Feasible Condition or Feasibility Condition (FC) DUAL Concepts Học viện mạng Bach Khoa - Website: www.bkacad.com 59 • Successor – The best least cost route to a destination found in the routing table • Feasible distance(FD) – The lowest calculated metric along a path to a destination network Successor and Feasible Distance Học viện mạng Bach Khoa - Website: www.bkacad.com 60 • Feasible Successor is a loop free backup route to same destination as successor route Feasible Successor Học viện mạng Bach Khoa - Website: www.bkacad.com 61 Successors and Feasible Successors Học viện mạng Bach Khoa - Website: www.bkacad.com 62 Successors and Feasible Successors Học viện mạng Bach Khoa - Website: www.bkacad.com 63 Successors and Feasible Successors Học viện mạng Bach Khoa - Website: www.bkacad.com 64 • Reported distance (RD) –The metric that a router reports to a neighbor about its own cost to that network • Feasibility Condition (FC) –Met when a neighbor’s RD is less than the local router’s FD to the same destination network Feasibility Condition and Reported Distance Học viện mạng Bach Khoa - Website: www.bkacad.com 65 Successors and Feasible Successors 172.30.1.0 172.30.1.0 Học viện mạng Bach Khoa - Website: www.bkacad.com 66 Successors and Feasible Successors Advertised or Destination Feasible Dist. Reported. Dist. Neighbor 172.30.1.0 40 30 X In Topology Table 172.30.1.0 31 21 Y In Routing Table 172.30.1.0 230 220 Z Not in Topology Table (show ip eigrp topology ) Current Successor = 31 RD of RTY= 21 Feasible Successor, FC: RD30 < FD31 FD to 172.30.1.0 is 31 via Router Y 172.30.1.0 RTZ is NOT Feasible Successor, FC: RD220 not< FD31 Học viện mạng Bach Khoa - Website: www.bkacad.com 67 Successors and Feasible Successors Current Successor = 31 RD of RTY= 21 Feasible Successor, FC: RD30 < FD31 FD to 172.30.1.0 is 31 via Router Y 172.30.1.0 • RTY is successor with a computed cost of 31. • “31” is the Feasible Distance (FD). • RTX is a feasible successor because its RD is less than or equal to the FD. - RTX’s RD (30) is less than the FD (31). RTZ is NOT Feasible Successor, FC: RD220 not< FD31 Học viện mạng Bach Khoa - Website: www.bkacad.com 68 Example of a Loop Cost=70Cost=19 RTZ has a Reported Distance to RTA of 220. Since its Reported Distance is greater than RTA’s own Feasibile Distance of 31, RTA can’t trust that the route RTZ takes is somehow back through itself. Học viện mạng Bach Khoa - Website: www.bkacad.com 69 DUAL Concepts Học viện mạng Bach Khoa - Website: www.bkacad.com 70 DUAL Concepts TheTopology table include: 1. all successor routes 2. all feasible successor routes 3. other routes updated by neighbors Học viện mạng Bach Khoa - Website: www.bkacad.com 71 DUAL Concepts • EIGRP Topology Table dissected Active state ? Học viện mạng Bach Khoa - Website: www.bkacad.com 72 DUAL Concepts No Feasible Successor Học viện mạng Bach Khoa - Website: www.bkacad.com 73 Query and Reply Packets RTZ replies that it still has a route to 172.30.1.0, while RTX and RTY reply that they do not. Current Successor is now RTZ, with a FD of 230 and a RD of RTZ= 220. Routes via RTY and RTX Fail! 172.30.1.0X ? RTZ was previously NOT a Feasible Successor, FC: RD220 not< FD31 or FD40, but now there is no Sucessor X Queries Replies Học viện mạng Bach Khoa - Website: www.bkacad.com 74 • 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 states • FSMs are used to describe how a device, computer program, or routing algorithm will react to a set of input events Finite State Machine (FSM) Học viện mạng Bach Khoa - Website: www.bkacad.com 75 • DUAL FSM – Selects a best loop-free path to a destination – Selects alternate routes by using information in EIGRP tables Finite State Machine Học viện mạng Bach Khoa - Website: www.bkacad.com 76 Finite State Machines (FSM): with Feasible Successor • To examine output from EIGRP’s finite state machine us the debug eigrp fsm command Finite State Machine Học viện mạng Bach Khoa - Website: www.bkacad.com 77 Học viện mạng Bach Khoa - Website: www.bkacad.com 78 Finite State Machine Finite State Machines (FSM): without Feasible Successor Học viện mạng Bach Khoa - Website: www.bkacad.com 79 Học viện mạng Bach Khoa - Website: www.bkacad.com 80 More EIGRP Configuration Học viện mạng Bach Khoa - Website: www.bkacad.com 81 The Null0 Summary Route Học viện mạng Bach Khoa - Website: www.bkacad.com 82 • The auto-summary command permits EIGRP to automatically summarize at major network boundaries • The no auto-summary command is used to disable automatic summarization – This causes all EIGRP neighbors to send updates that will not be automatically summarized – This will cause changes to appear in both • routing tables • topology tables Automatic Summarization Học viện mạng Bach Khoa - Website: www.bkacad.com 83 The no auto-summary Command Học viện mạng Bach Khoa - Website: www.bkacad.com 84 Disabling Automatic Summarization Học viện mạng Bach Khoa - Website: www.bkacad.com 85 More EIGRP Configurations • Disabling Automatic Summarization: topology table change Học viện mạng Bach Khoa - Website: www.bkacad.com 86 • Manual summarization can include supernets • Command used to configure manual summarization Router(config-if)# ip summary-address eigrp as-number network-address subnet- mask Manual Summarization Học viện mạng Bach Khoa - Website: www.bkacad.com 87 Manual Summarization Học viện mạng Bach Khoa - Website: www.bkacad.com 88 Manual Summarization Học viện mạng Bach Khoa - Website: www.bkacad.com 89 EIGRP Default Route Học viện mạng Bach Khoa - Website: www.bkacad.com 90 Gateway Router router igrp 24 network 207.21.20.0 ip route 0.0.0.0 0.0.0.0 207.21.20.1 ip default-network 207.21.20.0 Extra:EIGRP Default Route Học viện mạng Bach Khoa - Website: www.bkacad.com 91 router eigrp 100 network 10.0.0.0 ! interface serial 0 ip address 10.1.1.1 ip summary-address eigrp 100 0.0.0.0 0.0.0.0 Extra:EIGRP Default Route Học viện mạng Bach Khoa - Website: www.bkacad.com 92 EIGRP Default Route Học viện mạng Bach Khoa - Website: www.bkacad.com 93 Fine-Tuning EIGRP • EIGRP bandwidth utilization – By default, EIGRP uses only up to 50% of interface bandwidth for EIGRP information – The command to change the percentage of bandwidth used by EIGRP is Router(config-if)#ip bandwidth-percent eigrp as-number percent Học viện mạng Bach Khoa - Website: www.bkacad.com 94 More EIGRP Configurations • Hello intervals and hold times are configurable on a per-interface basis • Router(config-if)#ip hello-interval eigrp as-number seconds • Changing the hello interval also requires changing the hold time to a value greater than or equal to the hello interval • Router(config-if)#ip hold-time eigrp as-number seconds Học viện mạng Bach Khoa - Website: www.bkacad.com 95 EIGRP show commands Học viện mạng Bach Khoa - Website: www.bkacad.com 96 EIGRP debug commands Học viện mạng Bach Khoa - Website: www.bkacad.com 97 Extra:Authentication • MD5 cryptographic checksums are the only authentication supported in EIGRP, which on first consideration might seem less flexible than RIPv2 and OSPF, which support both MD5 and clear-text passwords. • However, clear-text password authentication should be used only when a neighboring device does not support the more secure MD5. Because EIGRP will be spoken only between two Cisco devices, this situation will never arise. Configuring EIRGP authentication • Step 1: Enter configuration mode for the interface on which you want to enable authentication. • Step 2: Specify MD5 authentication for EIGRP packets using the ip authentication mode eigrp 100 md5 command. Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com • Step 3: Enable the authentication of EIGRP packets with a key specified in a key chain by using the ip authentication key-chain eigrp ASNumber key-chain command. • Step 4: Enter the configuration mode for the key chain using the key chain key-chain(key-chain can be different in each side). • Step 5: Identify a key ID to use, and enter configuration mode for that key using the key key-id command. Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com Configuring EIRGP authentication • Step 6: Identify the key string (password) for this key using the key-string {key-string} command. (key-string must be the same on both side of EIGRP routers) Học viện mạng Cisco Bách Khoa - Website: www.ciscobachkhoa.com Configuring EIRGP authentication Học viện mạng Bach Khoa - Website: www.bkacad.com 101 Example of Authentication EIGRP redistribution • Planning Redistribution • Locate the boundary router between two routing processes. • Determine which routing process is the core or backbone process • Determine which routing process is the edge or migration process • Select a method for injecting the required edge protocol routes into the core. 102•Học viện mạng Bach Khoa - Website: www.bkacad.com Configuring redistribution into EIGRP • Use this command to redistribute routes into EIGRP: – Router(config-router)# redistribute protocol [process-id] [match {internal | external 1 | external 2}] [metric metric-value] [route-map map- tag] Học viện mạng Bach Khoa - Website: www.bkacad.com 103 •RtrA(config)# router eigrp 100 RtrA(config-router)# redistribute ospf ? Process ID •RtrA(config-router)# redistribute ospf 1 ? • match Redistribution of OSPF routes • metric Metric for redistributed routes • route-map Route map reference • • • Default metric is infinity.  Bandwidth in kilobytes = 10000kbps.  Delay in tens of microseconds = 100ms.  Reliability = 255 (maximum).  Load = 1 (minimum).  MTU = 1,500 bytes. Học viện mạng Bach Khoa - Website: www.bkacad.com 104 Configuring redistribution into EIGRP Học viện mạng Bach Khoa - Website: www.bkacad.com 105 Let's look at an example, there are three ways to get to Network X, from Router E: (Note: metrics incorrectly not including outgoing interface to Net X.) • E-B-A with a metric of 30 • E-C-A with a metric of 20 <<<-- Minimum Metric • E-D-A with a metric of 45 Extra:EIGRP variance command Học viện mạng Bach Khoa - Website: www.bkacad.com 106 variance 2 • This increases the minimum metric to 40 (2 * 20 = 40). • EIGRP includes all the routes that have a metric less than or equal to 40, and are feasible successors. • In the above configuration, EIGRP now uses two paths to get to Network X, E-C-A and E-B-A, because both paths have a metric under 40. router eigrp 1 network x.x.x.x variance 2 Extra:EIGRP variance command Học viện mạng Bach Khoa - Website: www.bkacad.com 107 Two unequal-cost paths: • E-B-A with a metric of 30 <<<-- Also below 2*20 • E-C-A with a metric of 20 <<<-- Minimum Metric • E-D-A with a metric of 45 EIGRP doesn't use path E-D-A because it has a metric of 45, and it's not a feasible successor. Can have up to 6 unequal cost paths. Extra:EIGRP variance command router eigrp 1 network x.x.x.x variance 2 Học viện mạng Bach Khoa - Website: www.bkacad.com 108 Extra:EIGRP Traffic Share • To control how traffic is distributed among routes when there are multiple routes for the same destination network that have different costs, use the traffic-share router configuration command. • To disable this function, use the no form of the command. traffic-share {balanced | min} no traffic share {balanced | min} balanced • Distributes traffic proportionately to the ratios of the metrics. min • Uses routes that have minimum costs • For more information: 9186a008009437d.shtml Học viện mạng Bach Khoa - Website: www.bkacad.com 109 Summary • Describe the background and history of EIGRP • Describe the features and operation of EIGRP • Examine the basic EIGRP configuration commands and identity 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 Học viện mạng Bach Khoa - Website: www.bkacad.com 110

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