© 2007 Cisco Systems, Inc. All rights reserved.Cisco Public ITE PC v4.0 Chapter 1 1 Routing Protocols and Concepts EIGRP Chapter 9 Modified by Pete Brierley.

ITE PC v4.0 Chapter 1 2 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public What will we Learn from chapter 9?  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.

ITE PC v4.0 Chapter 1 4 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Terms you MUST know RIPng Weights Hold time TLV Neighbor Table Routing Table Topology Table Bounded Updates Summary routes Quan zeros AS Wildcard mask IPv6 K values Reliability Load Delay Bandwidth Successor Feasible Distance RD FC Feasible Successor FSM Internal routes External routes OP Code PDM RTP Unicast Multicast Hello packet Adjacencies DUAL IANA Null 0 Aperiodic

ITE PC v4.0 Chapter 1 5 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public 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 -IGRP discontinued support starting with IOS 12.2(13)T & 12.2(R1s4)S

ITE PC v4.0 Chapter 1 6 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP EIGRP Message Format  EIGRP Header  Data link frame header - contains source and destination MAC address  IP packet header - contains source & destination IP address  EIGRP packet header - contains AS number  Type/Length/Field - data portion of EIGRP message

ITE PC v4.0 Chapter 1 7 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP  EIGRP packet header contains –Opcode field –Autonomous System number  EIGRP Parameters contains –Weights –Hold time

ITE PC v4.0 Chapter 1 8 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP  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

ITE PC v4.0 Chapter 1 9 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Protocol Dependent Modules (PDM)  EIGRP uses PDM to route several different protocols i.e. IP, IPX & AppleTalk  PDMs are responsible for the specific routing task for each network layer protocol

ITE PC v4.0 Chapter 1 10 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Reliable Transport Protocol (RTP)  Purpose of RTP –Used by EIGRP 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

ITE PC v4.0 Chapter 1 12 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP  Update packets –Used to propagate routing information  Acknowledgement packets –Used to acknowledge receipt of update, query & reply packets

ITE PC v4.0 Chapter 1 13 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP  Query & Reply packets  Used by DUAL for searching for networks  Query packets -Can use  Unicast  Multicast  Reply packet -Use only  unicast

ITE PC v4.0 Chapter 1 14 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP  Purpose of Hello Protocol –To discover & establish adjacencies with neighbor routers  Characteristics of hello protocol –Time interval for sending hello packet  Most networks it is every 5 seconds  Multipoint non broadcast multi-access networks –Unicast every 60 seconds -Holdtime  This is the maximum time router should wait before declaring a neighbor down  Default holdtime –3 times hello interval

ITE PC v4.0 Chapter 1 15 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP EIGRP Bounded Updates  EIGRP only sends update when there is a change in route status  Partial update –A partial update includes only the route information that has changed – the whole routing table is NOT sent  Bounded update –When a route changes, only those devices that are impacted will be notified of the change  EIGRP’s use of partial bounded updates minimizes use of bandwidth

ITE PC v4.0 Chapter 1 16 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Diffusing Update Algorithm (DUAL) –Purpose EIGRP’s primary method for preventing routing loops –Advantage of using DUAL Provides for fast convergence time by keeping a list of loop- free backup routes

ITE PC v4.0 Chapter 1 17 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP  Administrative Distance (AD) –Defined as the trustworthiness of the source route  EIGRP default administrative distances –Summary routes = 5 –Internal routes = 90 –Imported routes = 170

ITE PC v4.0 Chapter 1 22 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Basic EIGRP Configuration  Autonomous System (AS) & Process IDs –This is a collection of networks under the control of a single authority (reference RFC 1930) –AS Numbers are assigned by IANA –Entities needing AS numbers  ISP  Internet Backbone prodiers  Institutions connecting to other institutions using AS numbers

ITE PC v4.0 Chapter 1 23 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Basic EIGRP Configuration  EIGRP autonomous system number actually functions as a process ID  Process ID represents an instance of the routing protocol running on a router  Example Router(config)#router eigrp autonomous-system

ITE PC v4.0 Chapter 1 24 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Basic EIGRP Configuration The router eigrp command  The global command that enables eigrp is router eigrp autonomous-system -All routers in the EIGRP routing domain must use the same process ID number ( autonomous-system number)

ITE PC v4.0 Chapter 1 25 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Basic EIGRP Configuration The Network Command  Functions of the network command –Enables interfaces to transmit & receive EIGRP updates –Includes network or subnet in EIGRP updates  Example –Router(config-router)#network network-address

ITE PC v4.0 Chapter 1 26 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Basic EIGRP Configuration  The network Command with a Wildcard Mask -This option is used when you want to configure EIGRP to advertise specific subnets -Example Router(config-router)#network network-address [wildcard-mask]

ITE PC v4.0 Chapter 1 27 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Basic EIGRP Configuration Verifying EIGRP  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

ITE PC v4.0 Chapter 1 29 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Basic EIGRP Configuration Examining the Routing Table  The show ip route command is also used to verify EIGRP  EIGRP routes are denoted in a routing table by the letter “D”  By default, EIGRP automatically summarizes routes at major network boundary

ITE PC v4.0 Chapter 1 30 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Basic EIGRP Configuration  Introducing the Null0 Summary Route –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  At least one subnet is learned via EIGRP  Automatic summarization is enabled

ITE PC v4.0 Chapter 1 31 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Basic EIGRP Configuration  R3’s routing table shows that the 172.16.0.0/16 network is automatically summarized by R1 & R3

ITE PC v4.0 Chapter 1 32 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Metric Calculation EIGRP Composite Metric & the K Values  EIGRP uses the following values in its composite metric -Bandwidth, delay, reliability, and load  The composite metric used by EIGRP –formula used has values K1  K5 K1 & K3 = 1 all other K values= 0

ITE PC v4.0 Chapter 1 34 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Metric Calculation EIGRP Metrics  Use the show interfaces command to view metrics  EIGRP Metrics Bandwidth – EIGRP uses a static bandwidth to calculate metric Most serial interfaces use a default bandwidth value of 1.544Mbos (T1)

ITE PC v4.0 Chapter 1 35 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Metric Calculation EIGRP Metrics  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

ITE PC v4.0 Chapter 1 36 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Metric Calculation  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

ITE PC v4.0 Chapter 1 37 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Metric Calculation Using the Bandwidth Command  Modifying the interface bandwidth -Use the bandwidth command -Example Router(config-if)#bandwidth kilobits  Verifying bandwidth –Use the show interface command  Note – bandwidth command does not change the link’s physical bandwidth

ITE PC v4.0 Chapter 1 39 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP 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 delays  EIGRP Metric = calculated BW + calculated delay

ITE PC v4.0 Chapter 1 44 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public DUAL Concepts  Successor The best least cost route to a destination found in the routing table  Feasible distance The lowest calculated metric along a path to a destination network

ITE PC v4.0 Chapter 1 45 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public DUAL Concepts Feasible Successors, Feasibility Condition & Reported Distance  Feasible Successor -This is a loop free backup route to same destination as successor route

ITE PC v4.0 Chapter 1 46 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public DUAL Concepts  Reported distance (RD) -The metric that a router reports to a neighbor about its own cost to that network Feasible Successors, Feasibility Condition & Reported Distance

ITE PC v4.0 Chapter 1 47 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public DUAL Concepts  Feasibility Condition (FC) -Met when a neighbor’s RD is less than the local router’s FD to the same destination network

ITE PC v4.0 Chapter 1 49 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public DUAL Concepts Topology Table: No Feasible Successor  A feasible successor may not be present because the feasibility condition may not be met -In other words, the reported distance of the neighbor is greater than or equal to the current feasible distance

ITE PC v4.0 Chapter 1 51 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public DUAL Concepts  Finite 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 states –FSMs are used to describe how a device, computer program, or routing algorithm will react to a set of input events

ITE PC v4.0 Chapter 1 52 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public DUAL Concepts  DUAL FSM –Selects a best loop- free path to a destination –Selects alternate routes by using information in EIGRP tables

ITE PC v4.0 Chapter 1 53 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public DUAL Concepts Finite State Machines (FSM)  To examine output from EIGRP’s finite state machine us the debug eigrp fsm command

ITE PC v4.0 Chapter 1 54 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public More EIGRP Configurations The Null0 Summary Route  By default, EIGRP uses the Null0 interface to discard any packets that match the parent route but do not match any of the child routes  EIGRP automatically includes a null0 summary route as a child route whenever both of the following conditions exist –One or subnets exists that was learned via EIGRP –Automatic summarization is enabled

ITE PC v4.0 Chapter 1 56 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public More EIGRP Configurations Disabling Automatic Summarization  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

ITE PC v4.0 Chapter 1 57 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public More EIGRP Configurations Manual Summarization  Manual summarization can include supernets Reason: EIGRP is a classless routing protocol & include subnet mask in update  Command used to configure manual summarization –Router(config-if)#ip summary-address eigrp as-number network-address subnet-mask

ITE PC v4.0 Chapter 1 59 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public More EIGRP Configurations EIGRP Default Routes  “quad zero” static default route -Can be used with any currently supported routing protocol -Is usually configured on a router that is connected a network outside the EIGRP domain  EIGRP & the “Quad zero” static default route –Requires the use of the redistribute static command to disseminate default route in EIGRP updates

ITE PC v4.0 Chapter 1 60 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public More EIGRP Configurations 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

ITE PC v4.0 Chapter 1 61 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public More EIGRP Configurations  Configuring Hello Intervals and Hold Times -Hello intervals and hold times are configurable on a per-interface basis -The command to configure hello interval is 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 -The command to configure hold time value is Router(config-if)#ip hold-time eigrp as-number seconds

ITE PC v4.0 Chapter 1 62 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Summary  Background & History –EIGRP is a derivative of IGRP  EIGRP is a Cisco proprietary distance vector routing protocol released in 1994  EIGRP terms and characteristics –EIGPR uses RTP to transmit & receive EIGRP packets –EIGRP has 5 packet type:  Hello packets  Update packets  Acknowledgement packets  Query packets  Reply packets –Supports VLSM & CIDR

ITE PC v4.0 Chapter 1 63 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Summary  EIGRP terms and characteristics –EIGRP uses a hello protocol  Purpose of hello protocol is to discover & establish adjacencies –EIGRP routing updates  Aperiodic  Partial and bounded  Fast convergence

ITE PC v4.0 Chapter 1 64 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Summary  EIGRP commands –The following commands are used for EIGRP configuration  RtrA(config)#router eigrp [autonomous-system #]  RtrA(config-router)#network network-number –The following commands can be used to verify EIGRP  Show ip protocols  Show ip eigrp neighbors  Show ip route

ITE PC v4.0 Chapter 1 66 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Summary  DUAL –Purpose of DUAL  To prevent routing loops –Successor  Primary route to a destination –Feasible successor  Backup route to a destination –Feasible distance  Lowest calculated metric to a destination –Reported distance  The distance towards a destination as advertised by an upstream neighbor

ITE PC v4.0 Chapter 1 67 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Summary  Choosing the best route –After router has received all updates from directly connected neighbors, it can calculate its DUAL  1 st metric is calculated for each route  2 nd route with lowest metric is designated successor & is placed in routing table  3 rd 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

ITE PC v4.0 Chapter 1 68 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Summary  Automatic summarization –On by default –Summarizes routes on classful boundary –Summarization can be disabled using the following command  RtrA(config-if)#no auto-summary

ITE PC v4.0 Chapter 1 71 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary routing protocol based on IGRP. EIGRP supports CIDR, and hence VLSM. Compared to IGRP, EIGRP boasts faster convergence times, improved scalability and superior handling of routing loops. Technically, EIGRP is an advanced distance-vector routing protocol that relies on features commonly associated with link-state protocols. Some of OSPF’s best traits, such as partial updates & neighbor discovery, are similarly put to use by EIGRP.

ITE PC v4.0 Chapter 1 72 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Recall that OSPF’s strengths include scalability and multi- vendor support. So if your core routers are a mixed bag of products from several different vendors, OSPF and RIP may be your only options. But OSPF’s benefits, especially it’s hierarchical design, come at a price: administrative complexity. EIGRP is an ideal choice for large, multiprotocol networks built primarily on Cisco routers (says Cisco).

ITE PC v4.0 Chapter 1 73 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Comparison of OSPF and EIGRP OSPF EIGRP Supports CIDR & VLSM, rapid convergence, partial updates, neighbor discovery. Supports CIDR & VLSM, rapid convergence, partial updates, neighbor discovery Enables the admin to define route summarization. Uses automatic route summarization & user-defined route summaries. Is an open standard; has multi-vendor support Is proprietary; can only be used with Cisco routers. Is scalable; admin defined ‘areas’ provide manageable hierarchy. Is scalable; no hierarchical domains exist Is difficult to implementIs easy to implement.

ITE PC v4.0 Chapter 1 74 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP and IGRP Compatibility EIGRP offers multiprotocol support and IGRP does not. EIGRP scales IGRP’s metric by a factor of 256. That’s because EIGRP uses a metric that is 32 bits long, & IGRP uses a 24-bit metric. By dividing or multiplying by 256, EIGRP can easily exchange information with IGRP. EIGRP imposes a max hop limit of 224, where IGRP has 255.

ITE PC v4.0 Chapter 1 75 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Sharing or redistribution, is automatic between IGRP & EIGRP as long as both processes use the same AS number. metric = [K1 x bandwidth + K2 x bandwidth) / (256ms – load) + (K3 x delay)] x [K5 / (reliability+K4)] Where by default: K1 = 1 K2 = 0 K3 = 1 K4 = 0 K5 = 0 EIGRP and IGRP Compatibility

ITE PC v4.0 Chapter 1 76 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP tags routes learned from IGRP as external because they did not originate from EIGRP routers. External EIGRP routes are denoted by EX in the routing table. But IGRP cannot differentiate between internal & external routes EIGRP vs. IGRP

ITE PC v4.0 Chapter 1 77 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP EIGRP is an advanced distance vector routing protocol, but has advantages over simple distance vector protocols: rapid convergence By using an routing algorithm, Diffusing Update Algorithm (DUAL) which guarantees loop-free operation & allows all routers involved in a topology change to synchronize at the same time. partial bounded updates EIGRP routers make partial, incremental updates, & unlike OSPF, the routers send these partial updates only to the routers that need the information. This is called bounded updates.

ITE PC v4.0 Chapter 1 78 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP cont. minimal consumption of bandwidth when the network is stable No timed routing updates - instead small hello packets. Exchanged a regular intervals don’t use a significant amount of bandwidth. support for VLSM and CIDR multiple network-layer support EIGRP supports IP, IPX and AppleTalk via protocol- dependent modules (PDM). complete independence from routed protocols PDM protect EIGRP from painstaking revision.

ITE PC v4.0 Chapter 1 79 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Terminology & Tables EIGRP routers keep route and topology information in RAM for quick access. EIGRP terms and tables: neighbor table Maintains a neighbor table that list adjacent routers. There is a neighbor table for each protocol that EIGRP supports. topology table Topology table for each configured network protocol. All learned routes to a destination are maintained in the topology table. routing table EIGRP chooses the best (successor) routes to a destination from the topology table & places these routes in the routing table.

ITE PC v4.0 Chapter 1 80 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public successor a route selected as the primary route used to reach a destination. Successors are kept in the routing table. feasible successor Is a backup route. They are kept in the topology table. EIGRP routers establish adjacencies with neighbor routers by sending hello packets, sent every 5 seconds (default). By forming adjacencies, EIGRP routers do the following: dynamically learn of new routes that join their network identify routers that become either unreachable or inoperable rediscover routers that had previously been unreachable. EIGRP Terminology

ITE PC v4.0 Chapter 1 81 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Technologies cont. Reliable Transport Protocol (RTP) is a transport layer (layer 4) protocol that can guarantee ordered delivery of EIGRP packets to all neighbors. To stay independent of IP, EIGRP uses its own proprietary transport-layer protocol to guarantee delivery of routing information. EIGRP uses RTP to provide reliable or unreliable service as the situation warrants. Hello packets are not required to be reliable delivery. RTP supports both unicasting & multicasting, and it can multicast and unicast to different peers simultaneously. The centerpiece of EIGRP is DUAL, the EIGRP route calculation engine. It uses a finite state machine. DUAL tracks all the routes advertised by neighbors and uses the composite metric of each route to compare them. DUAL also guarantees that each path is loop-free.

ITE PC v4.0 Chapter 1 82 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Technologies cont. A successor is a neighboring router that is currently used for packet forwarding; it provides the least cost route to the destination and is not part of the routing loop A feasible successor provides the next lowest cost path without introducing routing loops.

ITE PC v4.0 Chapter 1 84 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Data Structure Neighbor Table the most important table in EIGRP. The neighbor relationships in the neighbor table are basis for all EIGRP routing updates and convergence activity. supports reliable, sequenced delivery of packets. Routing Table Contain the routes installed by DUAL as the best loop free paths to a given destination. It canmaintain up to 4 routes per destination. Topology Table stores all the information it needs to calculate a set of distances and vectors to all reachable destinations.

ITE PC v4.0 Chapter 1 85 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Data Structure Reported distance (RD) The distance reported by an adjacent neighbor to a specific destination. Feasible distance (FD) The lowest calculated metric to each destination. Table is sorted with the successor routes at the top, followed by feasible successors. At the bottom are what DUAL believes are routing loops.

ITE PC v4.0 Chapter 1 86 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public To see the topology table, use the command: Router# show ip eigrp topology [all] Example of output: P 10.2.0.0/16, 1 successors, FD is 2681856, serno 33 via 10.2.0.2 (2681856/2169856), Serial1 Viewing (2681856/2169856), 2681856 is the FD, and 2169856 is the RD. If no feasible successors to the destination exist, DUAL places the route in the active state. Entries in the topology table can be in one of 2 states passive route – route that is stable and available for use active route – route in the process of being recomputed by DUAL.

ITE PC v4.0 Chapter 1 87 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Internal routes originate from within the EIGRP AS. External routes originate from outside the system. Routes learned (redistributed) from other routing protocols such as RIP, OSPF and IGRP are external. Static routes originating from outside the EIGRP AS and redistributed inside are also external routes. NOTE: The internal administrative distance of EIGRP is 90.

ITE PC v4.0 Chapter 1 88 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Packet Types EIGRP relies on 5 packet types to maintain its various tables and establish complex relationships with neighbor routers. The 5 packet types: 1. Hello 2. Acknowledgment 3. Update 4. Query 5. Reply

ITE PC v4.0 Chapter 1 89 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Hello Packets EIGRP relies on hello packets to discover, verify & rediscover neighbor routers. The default hello interval depends on the bandwidth of the interface: BandwidthExample LinkDefault HelloDefault Hold IntervalTime Less than 1.544MbpsMultipoint Frame Relay60 sec180 sec Greater than 1.544MbpsT1, Ethernet5 sec15 sec Keep the hold timer 3 times the hello interval. EIGRP hello packets are multicast. On IP networks, EIGRP routers send hellos to the multicasts IP address 224.0.0.10. Recall that OSPF requires neighbor routers to have the same hello & dead intervals to communicate. EIGRP has no such restriction.

ITE PC v4.0 Chapter 1 90 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Acknowledgement Packets An EIGRP router uses acknowledgement packets to indicate receipt of any EIGRP packet during a reliable exchange. To be reliable, a sender’s message must be acknowledged by the recipient. Hello packets are always sent unreliable, & require no acknowledgement. Update Packets Update packets are used when a router discovers a new neighbor. They are also used when a router detects a topology change. All update packets are sent reliably.

ITE PC v4.0 Chapter 1 91 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Query and Reply Packets EIGRP routers use query packets whenever they need specific information from one or all of its neighbors. A reply packet is used to respond to a query. Query can be multicast or unicast Replies are always unicast. Both packet types are sent reliably.

ITE PC v4.0 Chapter 1 92 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Convergence (DUAL) DUAL’s sophisticated algorithm results in EIGRP’s exceptional fast convergence, says Cisco A router’s topology table includes a list of all routes advertised by the neighbors. For each network, the router keeps the real (computed) cost of getting to that network & also keeps the advertised cost (reported distance) from its neighbor.

ITE PC v4.0 Chapter 1 93 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public The best path is the path with the lowest metric route that is calculated by adding the metric between the next-hop router and the destination (the reported distance) to the metric between the local router and the next- hop router. This computed cost, or distance is the FD. The next-hop router(s) are selected as the best path is the successor. If several routes have the same FD, then there can be several successors to a destination. EIGRP Convergence (DUAL)

ITE PC v4.0 Chapter 1 94 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public RTA RTX RTZ FDDI Network 24 RTY COST Serial 10 100 10 20 1 NeighborComputed Cost to 24Report Distance to 24 RTX 40 30 RTY 31 21 RTZ 230 220 10 For RTA, RTY is the successor to Network 24, because it has the lowest computed cost (31). Hence RTA’s FD=31. If RTY goes down, then is there a feasible successor – or not? If so, what is it? RTA reaches Network 24 via:

ITE PC v4.0 Chapter 1 95 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public RTA RTX RTZ FDDI Network 24 RTY COST Serial 10 100 10 20 1 NeighborComputed Cost to 24Report Distance to 24 RTX 40 30 RTY 31 21 RTZ 230 220 10 Feasible successor = 1.It’s RD < RTA’s FD AND 2.Has the lowest computed cost of all other routes DUAL calculates the feasible successor to be through RTX Remember: RTA’s FD=31

ITE PC v4.0 Chapter 1 96 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public RTA RTX RTZ FDDI Network 24 RTY COST Serial 10 100 10 20 1 NeighborComputed Cost to 24Reported Distance to 24 RTX 40 30 RTY 31 21 RTZ 230 220 10 Feasible successor = 1.It’s RD < RTA’s FD AND 2.Has the lowest computed cost of all other routes Suppose RTX also goes down. Is there a feasible successor for RTA to Network 24? NO! DUAL will set the route to Network 24 from passive to active state, and RTA will query its neighbor’s about Network 24 again.

ITE PC v4.0 Chapter 1 97 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Consider the output from the command ‘show ip eigrp topology all’: P 10.2.0.0/16, 1 successors, FD is 2681856, serno 33 via 10.2.0.2 (2681856/2169856), Serial0 via 10.2.1.2 (2681856/2169856), Serial1 via 10.2.2.2 (2891856/2769856), Ethernet 0 Remember: Successor is the route that has the best lowest cost or FD. Feasible successor = It’s RD < link’s FD AND has the lowest computed cost of all other routes

ITE PC v4.0 Chapter 1 98 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Consider the output from ‘show ip eigrp topology all’: P 10.2.0.0/16, 1 successors, FD is 2681856, serno 33 via 10.2.0.2 (2681856/2169856), Serial0 via 10.2.1.2 (2681856/2169856), Serial1 via 10.2.2.2 (2891856/2769856), Ethernet 0 What are the successor(s)? 10.2.0.2 AND 10.2.1.2 What are the feasible successor(s)? NONE

ITE PC v4.0 Chapter 1 99 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public EIGRP Operation The 4 key steps to EIGRP operation are: 1. building the neighbor table 2. discovering routes 3. choosing routes 4. maintaining routes Choose the routes based on these 5 factors: 1. bandwidth 2. delay 3. reliability 4. load 5. MTU (maximum transmission unit) So, unless otherwise configured by an administrator, bandwidth & delay are the only 2 factors that determine EIGRP’s metric value.

ITE PC v4.0 Chapter 1 100 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Configuring EIGRP Configuring EIGRP for IP Networks Router(config)# router eigrp autonomous-system- number Router(config-router)# network network-number network-number is the NETWORK address of the interface of the router

ITE PC v4.0 Chapter 1 101 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Configuring EIGRP The ip bandwidth-percent command configures the percentage of bandwidth that EIGRP can use on an interface. By default, EIGRP is set to use up to 50 percent of the bandwidth of an interface to exchange routing information. The command relies on the bandwidth of an interface. Some cases the engineer sets the bandwidth to a lower number than the actual bandwidth of the link (in order to manipulate the routing metric).

ITE PC v4.0 Chapter 1 102 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Summarizing EIGRP routes for IP EIGRP automatically summarizes routes at a classful boundary. For discontiguous subnetworks, you do NOT want summarization. The command that turns summarization off on EIGRP is: Router(config-router)# no auto- summary Hence, with summarization turned off, EIGRP routers will advertise subnets.

ITE PC v4.0 Chapter 1 103 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Manual summary routes are configured on a per-interface basis by: Router(config-if)#ip summary-address eigrp autonomous-system-number ip-address mask administrative-distance By default, EIGRP summary routes have an administrative distance of 5. The value can range between 1 and 255. Summarizing EIGRP routes for IP

ITE PC v4.0 Chapter 1 104 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public What did I Learn from chapter 9?  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.

© 2007 Cisco Systems, Inc. All rights reserved.Cisco Public ITE PC v4.0 Chapter 1 1 Routing Protocols and Concepts EIGRP Chapter 9 Modified by Pete Brierley.

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© 2007 Cisco Systems, Inc. All rights reserved.Cisco Public ITE PC v4.0 Chapter 1 1 Routing Protocols and Concepts EIGRP Chapter 9 Modified by Pete Brierley.

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Presentation on theme: "© 2007 Cisco Systems, Inc. All rights reserved.Cisco Public ITE PC v4.0 Chapter 1 1 Routing Protocols and Concepts EIGRP Chapter 9 Modified by Pete Brierley."— Presentation transcript:

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