ca ex s2m9 eigrp.ppt [compatibility mode]

8/3/2019 CA Ex S2M9 EIGRP.ppt [Compatibility Mode]

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Chapter 9: EIGRP

CCNA Ex loration version 4.0

1


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Objectives

Describe the background and history of EnhancedInterior Gateway Routing Protocol (EIGRP).

Examine the basic EIGRP configuration commandsand identify their purposes.

Calculate the composite metric used by EIGRP.

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Describe the concepts and operation of DUAL. Describe the uses of additional configuration

commands in EIGRP.


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Introduction to EIGRP



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EIGRP


e ma n purpose n sco s eve opmen o was o crea e a c ass essversion of IGRP.

EIGRP includes several features that are not commonly found in other distancevector routing protocols like RIP (RIPv1 and RIPv2) and IGRP.

These features include:1. Reliable Transport Protocol (RTP)

2. Bounded Updates3. Diffusing Update Algorithm (DUAL)4. Establishing Adjacencies5. Neighbor and Topology Tables

Although EIGRP may act like a link-state routing protocol, it is still a distance

vector routing protocol.


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EIGRP

Roots of EIGRP: IGRP Developed in 1985 to overcome

RIPv1s 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


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IGRP to EIGRP

Enhanced Distance Vector RoutingProtocol: EIGRP

Uses the Diffusing Update Algorithm

(DUAL) Does not age out routing entries noruses periodic updates.

Maintains a topology table separate

Traditional Distance VectorRouting Protocols

Use the Bellman-Ford orFord-Fulkerson algorithm.

Age out routing entries anduses periodic updates.


,

includes the best path and any loop-free backup paths.

When a route becomes unavailable,DUAL will use a backup path if oneexists in the topology table.

Faster convergence due to theabsence of holddown timers and asystem of coordinated routecalculations.

routes; the best path to adestination network.

When a route becomesunavailable, the router must

wait for a new routingupdate.

Slower convergence due toholddown timers.


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EIGRP Capabilities and Attributes



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EIGRP Message Format


The data portion of an EIGRP message is encapsulated in a packet.This data field is called Type/Length/Value or TLV.


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The Autonomous System (AS)Number specifies the EIGRProuting process.

Unlike RIP, Cisco routerscan run multi le instances of



EIGRP. The AS number is used to

track multiple instances of

EIGRP.

EIGRP Parameters contains Weights

Hold time


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TLV: IP internal contains Metric field



u ne mas e

Destination field

TLV: IP external contains Fields used when external

routes are imported intoEIGRP routing process


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Protocol Dependent Modules (PDM)



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RTP and EIGRP Packet Types



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Purpose of RTP: to transmit and receive EIGRPpackets

Characteristics of RTPInvolves both reliable & unreliable delivery of

EIGRP packet



Reliable delivery requires acknowledgment fromdestination

Unreliable delivery does not require an

acknowledgement from destinationPackets can be sent

Unicast

Multicast : Using address 224.0.0.10


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Hello Protocol



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Update packetsUsed to propagate routing information

Update packets are sent as amulticast when required by multiple


,by only a single router.

Acknowledgement packets

Used to acknowledge receipt ofupdate, query & reply packetsEIGRP acknowledgement packets are

always sent as an unreliable unicast.


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Query & Reply packets

Used by DUAL for searching fornetworks

uer ackets: can use:


Unicast

Multicast

Reply packet: use only

unicast


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EIGRP Bounded Updates


EIGRPs use of partial boundedupdates minimizes use of bandwidth


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Diffusing Update Algorithm (DUAL)

Purpose:EIGRPs primary method for

DUAL: An Introduction


preventing routing loopsAdvantage:

Provides for fast convergencetime by keeping a list of loop-

free backup routes


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Administrative Distance



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Authentication


Note: Authentication does not encrypt the

router's routing table


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Basic EIGRP Configuration



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EIGRP Network Topology


Network Topology

Topology used is the same as previous chapters with

the addition of an ISP router


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An autonomous system (AS) is a collectionof networks under the administrativecontrol of a single entity that presents acommon routing policy to theInternet.(reference RFC 1930)

Autonomous System and Process IDs


Entities needing AS numbers ISP Internet Backbone providers Institutions connecting to other

institutionsusing AS numbers


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EIGRPautonomous

system numberactually functionsas a process ID



Process IDrepresents aninstance of the

routing protocolrunning on a router


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The router eigrpCommand


All routers in the EIGRP routing domainmust use the same process ID number(autonomous-system number)


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The networkCommand

Directly connected classful address


Functions of the network commandEnables interfaces to transmit & receive EIGRP

updates

Includes network or subnet in EIGRP updates


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The networkCommand

Router(config-router)#network network-address [wildcard-mask]

This option is used when you want to configure

EIGRP to advertise specific subnets



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EIGRP routers must establish adjacencies with their neighbors beforeany 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



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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 after16of these unicast retransmissions, theneighbor will be declared dead.

The time to wait for an ACK before switching from multicast to unicast isspecified by themulticast flowtimer.

Smooth Round Trip Timer (SRTT): the average elapsed time, measured inmilliseconds between the transmission of a acket to the nei hbor and the

Extra: Neighbor Table


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 IOSsoftware releases, any EIGRP packets received after the first hello will resetthe timer.

The formulas for calculating the exact values of the SRTT, the RTO, and themulticast flow timer are proprietary.


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RouterC#show ip eigrp neighbors

IP-EIGRP neighbors for process 44

H Address Interface Hold Uptime SRTT RTO Q Seq

(sec) (ms) CntNum

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

Extra: Neighbor Table


Neighbor address:The network-layer address of the neighborrouter(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 noEIGRP packets in the queue.

Sequence Number:The number of last packet that is received fromthat neighbor. EIGRP uses this field to acknowledge a neighborstransmission and to identify packets that are out of sequence.


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The show ip protocolscommand is used to verify that EIGRP is enabled

Verifying EIGRP



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Examining the Routing Table



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By default ,

EIGRPautomaticallysummarizes



routes atmajornetwork

boundary


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Introducting the Null0 Summary Route



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Null0 is not a physical interface In the routing table summary routes are

sourced from Null0 Reason: routes are used for

advertisement ur oses

Introducting the Null0 Summary Route


EIGRP will automatically include a null0summary route as child route when 2conditions are met:

1. At least one subnet is learned viaEIGRP2. Automatic summarization is

enabled


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au o-summary


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EIGRP Metric Calculation


EIGRP M t i C l l ti


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EIGRP C it M t i d th K V l


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Use the show ip protocols command to verify the Kvalues

EIGRP Composite Metric and the K Values




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Use the showinterfaces commandto view metrics

Bandwidth EIGRPuses a static



calculate metric Most serial interfaces

use a defaultbandwidth value of1.544Mbos (T1)



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Delay

Delay is the

defined as themeasure of time ittakes for a packet


to traverse a route it is a static valuebased on link type

to which interfaceis connected



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Reliability (not a default EIGRP metric)A measure of the likelihood that a link will fail

Measure dynamically & expressed as a fractionof 255 the higher the fraction the better thereliability



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 255The lower the fraction the less the load on the

link



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Router(config-if)#bandwidthkilobits

Note bandwidthcommand does not



physical bandwidth



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EIGRP uses the lowest bandwidth (BW) in itsmetric calculation:

Calculated BW = (reference BW / lowest BW(kbps)*256(reference BW = 107 )

Dela EIGRP uses the cumulative sum of all


outgoing interfaces:Calculated Delay = (the sum of outgoing interface delays/10)*256

EIGRP Metric = calculated BW + calculateddelay



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Calculate the metric from R2 to 192.168.1.0/24


Determining the costs


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S0/0 192.168.64.2/30 S0/1 192.168.64.6/30

Fa0/0 192.168.72.1/24

Calculated Bandwidth = (10,000,000/bandwidth kbps) * 256

Westasman

Bandwidth =

25,600

Delay =

2,560FastEthernet

= (10,000,000/100,000) * 256

= 25,600

T1

*

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S0/0 192.168.64.1/30 S0/0 192.168.64.5/30

Fa0/0 192.168.1.1/24

Fa0/0 192.168.1.2/24

EIGRP

AS 100

SanJose1SanJose2

Bandwidth =

1,657,856

=

512,000

= , ,

= 1,657,856

Determining the costs


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S0/0 192.168.64.2/30 S0/1 192.168.64.6/30

Fa0/0 192.168.72.1/24

Calculated Delay = (delay/10) * 256

Westasman

Bandwidth =

25,600

Delay =

2,560FastEthernet

= (100/10) * 256

= 2,560

T1

*


S0/0 192.168.64.1/30 S0/0 192.168.64.5/30

Fa0/0 192.168.1.1/24

Fa0/0 192.168.1.2/24

EIGRP

AS 100

SanJose1SanJose2

Bandwidth =

1,657,856

=

512,000

= ,

= 512,000

The Routing Table


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Administrative Distance / MetricSanJose2#show ip route

D 192.168.72.0/24 [90/2172416]

via 192.168.64.6, 00:28:26, Serial0


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Diffusing Update Algorithm (DUAL)


Diffusing Update Algorithm


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g p g


The design philosophy behind DUAL isthat even temporary routing loops aredetrimental to the performance of anetwork.

DUAL Concepts


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The Diffusing Update Algorithm (DUAL) isused to prevent looping:

Successor

Feasible Distance (FD)

p


Feasible Successor (FS)Reported Distance (RD) or Advertised

Distance (AD)

Feasible Condition or FeasibilityCondition (FC)

Successor and Feasible Distance


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SuccessorThe best least

cost route to adestinationfound in the


rout ng ta e

Feasibledistance(FD)

The lowest

calculatedmetric along apath to adestination

network

Feasible Successor


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Feasible Successor is a loopfree backup route to samedestination as successor route


Successors and Feasible Successors


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Feasibility Condition and Reported Distance


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Reported distance (RD)

The metric that a router reports to aneighbor about its own cost to that


Feasibility Condition (FC)Met when a neighbors RD is less

than the local routers FD to thesame destination network



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172.30.1.0


172.30.1.0



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Feasible Successor, FC: RD30 < FD31

172.30.1.0


Advertised orDestination 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 = 31RD of RTY= 21

FD to 172.30.1.0 is31 via Router Y

RTZ is NOT FeasibleSuccessor, FC:RD220 not< FD31



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Feasible Successor, FC: RD30 < FD31

172.30.1.0


Current Successor = 31RD of RTY= 21

FD to 172.30.1.0 is31 via Router Y

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.

- RTXs RD (30) is less than the FD (31).

RTZ is NOT FeasibleSuccessor, FC:RD220 not< FD31

Example of a Loop


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Cost=70Cost=19

RTZ has a Reported Distance toRTA of 220. Since its Reported

Distance is greater than RTAsown Feasibile Distance of 31,

RTA cant trust that the routeRTZ takes is somehow backthrough itself.

DUAL Concepts


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DUAL Concepts


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TheTopology table include:

1. all successor routes


. routes

3. other routes updatedby neighbors

DUAL Concepts


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EIGRP Topology Table dissected

Active state ?


DUAL Concepts


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No Feasible Successor


Query and Reply Packets


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172.30.1.0X

X

QueriesQueries

RepliesReplies


RTZ replies that it still has a route to 172.30.1.0, while RTX and RTY replythat they do not.

Current Successor is now RTZ, with a FD of 230 and a RD of RTZ= 220.

and RTX Fail!

?RTZ was previouslyNOT a FeasibleSuccessor, FC: RD220not< FD31 or FD40, but

now there is noSucessor

Finite State Machine (FSM)


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An abstract machine that defines a setof possible states something can go

through, what event causes thosestates and what events result form


those states FSMs are used to describe how a

device, computer program, or routingalgorithm will react to a set of inputevents

Finite State Machine


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DUAL FSMSelects a best

loop-free path toa destination


routes by usinginformation inEIGRP tables



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Finite State Machines (FSM): with Feasible Successor

To examine output from EIGRPs finite state machineus the debug eigrp fsmcommand



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Finite State Machines (FSM): without Feasible Successor



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More EIGRP Configuration


The Null0 Summary Route


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Automatic Summarization


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The auto-summarycommand permits EIGRPto automatically summarize at major networkboundaries

The no auto-summarycommand is used todisable automatic summarization


updates that will not be automaticallysummarized

This will cause changes to appear in both

routing tables

topology tables

The no auto-summaryCommand


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Disabling Automatic Summarization


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More EIGRP Configurations


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Disabling Automatic Summarization: topology table change


Manual Summarization


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Manual summarization can includesupernets

Command used to configure manualsummarization


Router(config-if)# ip summary-addresseigrp as-number network-address subnet-mask



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EIGRP Default Route


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Extra:EIGRP Default Route


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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


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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


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Fine-Tuning EIGRP

EIGRP bandwidth utilization


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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 byEIGRP is

Router(config-if)#ip bandwidth-percent eigrp as-number


More EIGRP Configurations

Hello intervals and hold times are configurable on a per-interface basis


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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 avalue greater than or equal to the hello interval

Router(config-if)#ip hold-time eigrp as-number seconds


EIGRP show commands


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EIGRP debug commands


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Extra:Authentication

MD5 cryptographic checksums are the only


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MD5 cryptographic checksums are the onlyauthentication supported in EIGRP, whichon first consideration might seem less

flexible than RIPv2 and OSPF, whichsupport both MD5 and clear-text passwords.


However, clear-text password authenticationshould be used only when a neighboringdevice does not support the more secureMD5. Because EIGRP will be spoken onlybetween two Cisco devices, this situationwill never arise.

Configuring EIRGP authentication

St 1 E t fi ti d f th i t f hi h


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Step 1: Enter configuration mode for the interface on which youwant to enable authentication.

Step 2: Specify MD5 authentication for EIGRP packets using the

ip authentication mode eigrp 100 md5 command.

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Step 3: Enable the authentication of EIGRP packets with a key



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Step 3: Enable the authentication of EIGRP packets with a keyspecified in a key chain by using the ip authentication key-chain

eigrp ASNumber key-chaincommand.

Step 4: Enter the configuration mode for the key chain using thekey chain key-chain(key-chaincan be differentin each side).

Step 5: Identify a key ID to use, and enter configuration mode fora ey us ng e ey ey- comman .


Step 6: Identify the key string (password) for this key using the



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Step 6: Identify the key string (password) for this key using thekey-string {key-string}command.

(key-stringmust be the sameon both side of EIGRP routers)


Example of Authentication


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EIGRP redistribution

Planning Redistribution


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g

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.

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Configuring redistribution into EIGRP

Use this command to redistribute routes into EIGRP:


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Router(config-router)# redistribute protocol

[process-id] [match {internal | external 1 |

external 2}] [metric metric-value] [route-map map-

tag]

RtrA(config)# router eigrp 100-


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.

Configuring redistribution into EIGRP


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Bandwidth in kilobytes = 10000kbps.

Delay in tens of microseconds = 100ms.

Reliability = 255 (maximum).

Load = 1 (minimum).

MTU = 1,500 bytes.


Extra:EIGRP variance command


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Let's look at an example, there are three ways to get to Network X, fromRouter E: (Note: metrics incorrectly not including outgoing interface toNet X.)

E-B-A with a metric of 30

E-C-A with a metric of 20


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router eigrp 1


variance 2

This increases the minimum metric to 40 (2 * 20 = 40).

EIGRP includes all the routes that have a metric less than or equalto 40, and are feasible successors.

In the above configuration, EIGRP now uses two paths to get toNetwork X, E-C-A and E-B-A, because both paths have a metricunder 40.

network x.x.x.x

variance 2

Extra:EIGRP variance command


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router eigrp 1


Two unequal-cost paths:

E-B-A with a metric of 30


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multiple routes for the same destination network that have differentcosts, 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:http://www.cisco.com/en/US/tech/tk365/tk207/technologies_tech_note09186a008009437d.shtml

Summary


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Describe the background and history of EIGRP

Describe the features and operation of EIGRP Examine the basic EIGRP configuration commands


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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