configuring enhanced igrp - university of...

© 2000, Cisco Systems, Inc. 6-1

Configuring EIGRPChapter 6

© 2000, Cisco Systems, Inc. www.cisco.com BSCN v1.0—6-2

ObjectivesObjectives

Upon completion of this chapter, you will be able to perform the following tasks:• Describe EIGRP features and operation• Explain how EIGRP discovers, chooses, and

maintains routes• Explain how EIGRP supports the use of VLSM• Explain how EIGRP operates in an NBMA

environment• Explain how EIGRP supports the use of route

summarization


Objectives (cont.)Objectives (cont.)

• Describe how EIGRP supports large networks • Configure EIGRP• Verify EIGRP operation• Given a set of network requirements, configure

an EIGRP environment and verify proper operation (within described guidelines)of your routers

• Given a set of network requirements, configureEIGRP in an NBMA environment andverify proper operation (within described guidelines) of your routers

© 2000, Cisco Systems, Inc. www.cisco.com 6-4

EIGRP Overview


• EIGRP supports:– Rapid convergence– Reduced bandwidth usage– Multiple network-layer protocols

What Is Enhanced IGRP (EIGRP)?What Is Enhanced IGRP (EIGRP)?

EnhancedIGRP

IPX RoutingProtocols

AppleTalk Routing Protocol

IP RoutingProtocols

IPX RoutingProtocols

AppleTalk Routing Protocol

IP RoutingProtocols


EIGRP FeaturesEIGRP Features

• Advanced distance vector• 100% loop free• Fast convergence• Easy configuration• Less network design constraints

than OSPF


EIGRP Features (cont.)EIGRP Features (cont.)

• Incremental updates•Supports VLSM and discontiguous networks•Classless routing•Compatible with existing IGRP networks•Protocol independent (supports IPX and AppleTalk)


Advantages of EIGRPAdvantages of EIGRP

• Uses multicast instead of broadcast• Utilizes link bandwidth and delay

– EIGRP metric = IGRP metric x 256(32 bit vs. 24 bit)

• Unequal cost path load balancing• More flexible than OSPF

– Manual summarization can be done in any interface at any router within the network


EIGRP—In IP PacketsEIGRP—In IP Packets

• EIGRP is an advanced distance vector routing protocol– Automatically establishes neighbor

relationships with peer devices– Relies on IP packets for delivery of routing

information

IP Header

Protocol Number

Frame Header

CRC

Packet Payload

Frame Payload

88 - EIGRP 6 - TCP17 - UDP

88 - EIGRP 6 - TCP17 - UDP


EIGRP Support for Different Topologies

EIGRP Support for Different Topologies

• EIGRP supports– Multiaccess (LANs)– Point-to-point (HDLC)– NBMA (Frame Relay)

S0A

B

S1

E

F

G

H

FrameRelay

D

CRest of the Core


EIGRP Support for IP AddressesEIGRP Support for IP Addresses

• EIGRP supports– Variable-length subnet masks (VLSMs)– Hierarchical designs

/16

D

/27

/30

/24

World

NM

A

PO

B

SR

C


EIGRP Support for Route Summarization

EIGRP Support for Route Summarization

• EIGRP performs route summarization– Classful network boundaries (default)– Arbitrary network boundaries (manual)

172.16.0.0 /24 10.0.0.0 /18192.168.42.0 /27

172.16.0.0 /16 172.16.0.0 /16192.168.42.0 /24


EIGRP TerminologyEIGRP Terminology

Neighbor Table—AppleTalkDestination Next Hop

RouterNeighbor Table—IPXDestination Next Hop

RouterNeighbor Table—IPNext-Hop InterfaceRouter






Topology Table—AppleTalkDestination 1 Next Router 1/CostDestination 1 Next Router 1/Cost

Topology Table—IPXDestination 1 Next Router 1/CostDestination 1 Next Router 1/Cost

Topology Table—IPDestination 1





Topology Table—IPDestination 1

Routing Table—AppleTalkDestination 1 Next Router XDestination 1 Next Router X

Routing Table—IPXDestination 1 Next Router XDestination 1 Next Router X

Routing Table—IPDestination 1








Topology Table—IPDestination 1 Successor



Routing Table—IPDestination 1 Successor








Topology Table—IPDestination 1 SuccessorDestination 1 Feasible Successor



Routing Table—IPDestination 1 Successor





EIGRP Operation


EIGRP PacketsEIGRP Packets

• Hello: Establish neighbor relationships• Update: Send routing updates• Query: Ask neighbors about

routing information• Reply: Response to query about

routing information• ACK: Acknowledgement of a reliable packet


EIGRP Neighbor RelationshipEIGRP Neighbor Relationship

• Two routers become neighbors when they see each other’s hello packet– Hello address = 224.0.0.10

• Hellos sent once every 5 seconds on the following links:– Broadcast media: Ethernet, Token Ring, FDDI– Point-to-point serial links: PPP, HDLC,

point-to-point Frame Relay/ATM subinterfaces– Multipoint circuits with bandwidth greater than

T1: ISDN PRI, SMDS, Frame Relay


EIGRP Neighbor Relationship (cont.)EIGRP Neighbor Relationship (cont.)

• Hellos sent once every 60 seconds on the following links:– Multipoint circuits with bandwidth less than

T1: ISDN BRI, Frame Relay, SMDS, and so on

• Neighbor declared dead when no EIGRP packets are received within hold interval– Not only hello can reset the hold timer

• Hold time by default is three times the hello time


EIGRP Neighbor Relationship (cont.)EIGRP Neighbor Relationship (cont.)

• EIGRP will form neighbors even though hello time and hold time don’t match

• EIGRP sources hello packets from primary address of the interface

• EIGRP will not form neighbor if K-values are mismatched

• EIGRP will not form neighbor if AS numbers are mismatched


What Is in a Neighbor Table?What Is in a Neighbor Table?

p2r2

p2r2#show ip eigrp neighborsIP-EIGRP neighbors for process 400H Address Interface Hold Uptime SRTT RTO Q Seq

(sec) (ms) Cnt Num1 172.68.2.2 To0 13 02:15:30 8 200 0 90 172.68.16.2 Se1 10 02:38:29 29 200 0 6


EIGRP ReliabilityEIGRP Reliability

• EIGRP reliable packets are packets that require explicit acknowledgement:– Update– Query– Reply

• EIGRP unreliable packets are packets that do not require explicit acknowledgement:– Hello– ACK


EIGRP Reliability (cont.)EIGRP Reliability (cont.)

• The router keeps a neighbor list and a retransmission list for every neighbor

• Each reliable packet (update, query, reply) will be retransmitted when packet is not acknowledged

• Neighbor relationship is reset when retry limit (limit = 16) for reliable packets is reached


EIGRP Reliability (cont.)EIGRP Reliability (cont.)

• EIGRP transport has window size of one (stop and wait mechanism)– Every single reliable packet needs to be

acknowledged before the next sequenced packet can be sent

– If one or more peers are slow in acknowledging, all other peers suffer from this

• Solution: The nonacknowledged multicast packet will be retransmitted as a unicast to the slow neighbor


I am router A, who is on the link?Hello

A B

1

Initial Route DiscoveryInitial Route Discovery


Here is my complete routing information. Update2

3



A B

1


Thanks for the information!Ack3

5

Here is my complete routing information.


Update2


A B

1


Topology Table

34

5


Thanks for the information!Ack3



A B

1


34Thanks for the information!Ack

3



A B

1


Here is my complete route information.Update

Topology Table

5

6



Converged

Thanks for the information! Ack 6

34Thanks for the information!Ack

3



A B

1

Here is my complete route information.Update5

Topology Table


•EIGRP uses a composite metric to pick the best path

EIGRP Route SelectionEIGRP Route Selection

IPX

19.2

T1

T1 T1

IPX

AppleTalk

IP

AppleTalk

IPA B

DC


EIGRP Metrics CalculationEIGRP Metrics Calculation

• Metric = [K1 x BW + (K2 x BW) / (256 - load) + K3 x delay] x [K5 / (reliability + K4)]– By default: K1 = 1, K2 = 0, K3 = 1, K4 = 0, K5 = 0

• Delay is sum of all the delays of the links along the paths– Delay = [Delay in 10s of microseconds] x 256

• Bandwidth is the lowest bandwidth of the links along the paths– Bandwidth = [10000000 / (bandwidth in Kbps)] x 256

• By default, metric = bandwidth + delay


EIGRP DUALEIGRP DUAL

• Diffusing Update Algorithm (DUAL)• Finite-state machine

– Tracks all routes advertised by neighbors– Select loop-free path using a successor and

remember any feasible successors– If successor lost:

• Use feasible successor– If no feasible successor:

• Query neighbors and recompute new successor


DUAL Example (Start) DUAL Example (Start)

E EIGRP FD AD Topology (a) 3 (fd)

via D 3 2 (Successor)via C 4 3

D EIGRP FD AD Topology(a) 2 (fd)

via B 2 1 (Successor)via C 5 3

C EIGRP FD AD Topology(a) 3 (fd)

via B 3 1 (Successor)via D 4 2 (fs)via E 4 3

(1)

(1)

(1)

(1)

(2)(2)

(a)

A

E

D

C

B


DUAL ExampleDUAL Example

(1)

(1)

(1)

(1)

(2)(2)

(a)

A

E

D

C

B XXX








DUAL Example (cont.)DUAL Example (cont.)

Q Q(1)

(1)

(1)

(2)(2)

(a)

A

E

D

C

B



D EIGRP FD AD Topology(a) **ACTIVE** -1 (fd)

via E (q)via C 5 3 (q)


via B 3 1 (Successor)via Dvia E 4 3



RR

Q

(1)

(1)

(1)

(2)(2)

(a)

A

E

D

C

B

E EIGRP FD AD Topology (a) **ACTIVE** -1 (fd)

via Dvia C 4 3 (q)


via E (q)via C 5 3


via B 3 1 (Successor)via Dvia E



RR

(1)

(1)

(1)

(2)(2)

(a)

A

E

D

C

B


via C 4 3 (Successor)via D


via E (q)via C 5 3





RR

(1)

(1)

(1)

(2)(2)

(a)

A

E

B




via C 5 3 (Successor)via E 5 4 (Successor)



D

C



(1)

(1)

(2)

(1)

(2)

(a)

A

E

D

C

B








DUAL Example (Start) DUAL Example (Start)

(1)

(1)

(1)

(1)

(2)(2)

(a)

A

E

D

C

B








DUAL Example (End)DUAL Example (End)

(1)

(1)

(1)

(2)(2)

(a)

A

E

D

C

B








Written Exercise


Configuring EIGRP


S2

Configuring EIGRP for IPConfiguring EIGRP for IP

router eigrp 109network 10.0.0.0network 172.16.0.0

10.1.0.0

10.2.0.0

172.16.4.0

172.16.3.0

172.16.2.0

172.16.7.0

10.4.0.0 172.16.6.0

172.16.5.0

172.16.1.0

T0

S0

S1192.168.1.0

TokenRing

TokenRing

• Network 192.168.0.0 is not configured on Router A because it is not directly connected to Router A

AS = 109

B

C

D

A

E


EIGRP Summarization—AutomaticEIGRP Summarization—Automatic

• Purpose: Smaller routing tables, smaller updates, query boundary

• Autosummarization:– On major network boundaries, subnetworks are

summarized to a single classful (major) network– Autosummarization is turned on by default

172.16.X.X

172.16.0.0/16

172.17.X.X


EIGRP Summarization—ManualEIGRP Summarization—Manual

• Manual summarization– Configurable on a per-interface basis in any

router within network– When summarization is configured on an

interface, the router immediate creates a route pointing to null zero

• Loop prevention mechanism– When the last specific route of the summary

goes away, the summary is deleted– The minimum metric of the specific routes is

used as the metric of the summary route


Configuring SummarizationConfiguring Summarization

(config-router)#

no auto-summary

• Turns off autosummarization for the EIGRP process

(config-if)#

ip summary-address eigrp <as-number><address> <mask>

• Creates a summary address to be generatedby this interface


Summarizing EIGRP Routes

router eigrp 1network 10.0.0.0 network no auto-summary

172.16.1.0

172.16.2.0

192.168.4.2

S0World

10.0.0.0A

BC


Summarizing EIGRP RoutesSummarizing EIGRP Routes

router eigrp 1network 10.0.0.0network 192.168.4.0!int s0ip address 192.168.4.2 255.255.255.0ip summary-address eigrp 1172.16.0.0 255.255.0.0

router eigrp 1network network 172.16.0.0no auto-summary

172.16.1.0

172.16.2.0

192.168.4.2

S0World

10.0.0.0A

BC


EIGRP Load BalancingEIGRP Load Balancing

• Routes with metric equal to the minimum metric will be installed in the routing table (equal-cost load balancing)

• Up to six entries in the routing table for the same destination– Number of entries is configurable– Default is four


EIGRP Unequal-Cost Load Balancing

EIGRP Unequal-Cost Load Balancing

• EIGRP offers unequal-cost load balancing– variance command

• Variance allows the router to include routes with a metric smaller than multipliertimes the minimum metric route to that destination– Multiplier is the number specified by the

variance command


10

20

10

10

20

25variance 2

Network Z(config)#

Variance ExampleVariance Example

• Router E will choose Router C to get to Network Z because FD = 20

• With variance of 2, Router E will also choose Router B to get to Network Z (20 + 10) < (2 x [FD])

• Router D will not be used to get to Network Z (45 > 40)

AE

D

C

B


Configuring WAN LinksConfiguring WAN Links

• EIGRP supports different WAN links– Point-to-point– NBMA

• Multipoint• Point-to-point

• EIGRP configurations must address– Bandwidth utilization– Overhead traffic associated with router

operation


EIGRP Bandwidth UtilizationEIGRP Bandwidth Utilization

• Specifies what percentage of bandwidth EIGRP packets will be able to utilize on this interface

• Uses up to 50% of the link bandwidth for EIGRP packets, by default– Used for greater EIGRP load control

(config-if)#

ip bandwidth-percent eigrp as-number <nnn>


Bandwidth over WAN InterfacesBandwidth over WAN Interfaces

• Bandwidth utilization over point-to-point subinterfaces using Frame Relay– Treats bandwidth as T1, by default– Best practice is to manually configure

bandwidth as the CIR of the PVC


Bandwidth over WAN Interfaces (cont.)


• Bandwidth over multipoint Frame Relay, ATM, SMDS, and ISDN PRI:– EIGRP uses the bandwidth on the main interface

divided by the number of neighbors on that interface to get the bandwidth information per neighbor




• Each PVC might have a different CIR, this might create an EIGRP packet pacing problem– Multipoint interfaces:

• Convert to point-to-point configuration, or

• Manually configure bandwidth = (lowest CIR x number of PVCs)


EIGRP WAN Configuration—Pure Multipoint

EIGRP WAN Configuration—Pure Multipoint

CIR 56

C

EF G

H

FrameRelay

S0

CIR 56 CIR 56

CIR 56

T1

interface serial 0encap frame-relaybandwidth 224

• All VCs share bandwidth evenly: 4 x 56 = 224


EIGRP WAN Configuration—Hybrid Multipoint

EIGRP WAN Configuration—Hybrid Multipoint

CIR 256BW 224

C

EF G

H

FrameRelay

S0

CIR 256BW 224

CIR 256BW 224

CIR 56BW 56

T1

• Lowest CIR x # of VC: 56 x 4 = 224

interface serial 0encap frame-relaybandwidth 224


EIGRP WAN Configuration—Hybrid Multipoint (Preferred)EIGRP WAN Configuration—Hybrid Multipoint (Preferred)

CIR 256BW 256

C

EF G

H

FrameRelay

S0

CIR 256BW 256

CIR 256BW 256

CIR 56BW 56

T1

interface serial 0.1 multipointbandwidth 768

interface serial 0.2 point-to-pointbandwidth 56

• Configure lowest CIR VC as point-to-point, specify BW = CIR• Configure higher CIR VCs as multipoint, combine CIRs

S0.1S0.2


EIGRP WAN Configuration—Pure Point-to-Point

EIGRP WAN Configuration—Pure Point-to-Point

CIR 56BW 25

C

EF G

H

FrameRelay

S0

CIR 56BW 25

CIR 56BW 25

CIR 56BW 25

256

interface serial 0.1 point-to-pointbandwidth 25ip bandwidth-percent eigrp 63 110

- -- -

interface serial 0.10 point-to-pointbandwidth 25ip bandwidth-percent eigrp 63 110

• Configure each VC as point-to-point, specify BW = 1/10 of link capacity• Increase EIGRP utilization to 50% of actual VC capacity

interface serial 0bandwidth 25ip bandwidth-percent eigrp 63 110

Hub and Spokewith 10x VCs


Using EIGRP inScalable

Internetworks


Factors that InfluenceEIGRP Scalability

Factors that InfluenceEIGRP Scalability

• EIGRP is not plug-and-play for large networks

• Limit EIGRP query range!• Quantity of routing information

exchanged between peers– Advertise major network or default

route to regions or remotes


EIGRP Query ProcessEIGRP Query Process

• Queries are sent out when a route is lost and no feasible successor is available

• The lost route is now in active state• Queries are sent out to all of its neighbors on

all interfaces except the interface tothe successor

• If the neighbor does not have the lost route information, queries are sent out to their neighbors


EIGRP Query Process (cont.)EIGRP Query Process (cont.)

• The router will have to get ALL of the replies from the neighbors before the router calculates the successor information

• If any neighbor fails to reply the query in 3 minutes, this route is stuck in active and the router resets the neighbor that fails to reply

• Solution for stuck in active is to limit the query range, also known as query scoping


AS 1AS 2

Network X

Query for XReply for XQuery for X

EIGRP Query RangeEIGRP Query Range

•Autonomous system boundaries– Contrary to popular belief, queries are not

bounded by AS boundaries. Queries from AS 1 will be propagated to AS 2.

XXA CB

13 2

10.1.0.0 10.2.0.0


172.130.1.0/24

B Summarizes 172.130.0.0/16 to A

172.x.x.x

Reply with Infinity and theQuery Stops Here!

Query for172.130.1.0/24

XX192.x.x.x

Query for172.130.1.0/24

EIGRP Query Range (cont.)EIGRP Query Range (cont.)

• Summarization point– Auto or manual summarization is the best way

to bound queries– Requires a good address allocation scheme

A CB

13

2


Limiting Size/Scope of Updates/Queries

Limiting Size/Scope of Updates/Queries

• Evaluate routing requirements– What routes are needed where?

• Once needs are determined:– Use summary address– Use filters


10.1.8.0/24

Regional Offices Remote Sites

XQueriesQueriesRepliesReplies

Limiting Updates/Queries—Example


B

A

E

D

C


10.1.8.0/24





B

A

E

D

C


LimitingUpdates/Queries—RealityLimitingUpdates/Queries—Reality

• Remote routers are fully involvedin convergence– Most remote routers are never

intendedto be transit

– Convergence complicated throughlack of information hiding


10.1.8.0/24



•ip summary-address eigrp 1 10.0.0.0 255.0.0.0 on all outbound interfaces to remotes

Limiting Updates/Queries—Better


B

A

E

D

C


10.1.8.0/24



•ip summary-address eigrp 1 10.0.0.0 255.0.0.0 on all outbound interfaces to remotes



B

A

E

D

C


Limiting Updates/Queries—Summary

Limiting Updates/Queries—Summary

• Convergence simplified by adding the summary-address statements– Remote routers just reply when queried,

do not forward queries


EIGRP Scalability RulesEIGRP Scalability Rules

• EIGRP is a very scalable routing protocol if proper design methods are used:– Good allocation of address space

• Each region should have a contiguous address space so route summarization is possible

– Have a tiered network design model


Core

TokenRing

TokenRing

3.3.4.01.1.1.0

3.3.4.0

1.1.4.0

3.3.3.0

2.2.1.0

1.1.3.0

3.3.1.0

1.1.2.02.2.3.0

2.2.2.0

TokenRing

TokenRing

TokenRing

TokenRing

1.1.1.01.1.2.02.2.3.03.3.4.0

2.2.1.03.3.2.03.3.3.01.1.4.0

3.3.1.02.2.2.01.1.3.0

• Bad addressing scheme– Subnets are everywhere throughout entire network

• Queries not bounded

Nonscalable Network—Example

Nonscalable Network—Example


Core

3.0.0.0

2.0.0.0

TokenRing

TokenRing

1.1.4.01.1.1.0

3.3.4.0

3.3.4.0

3.3.3.0

3.3.1.0

2.2.3.0

2.2.1.0

1.1.3.0

1.0.0.0

TokenRing

TokenRing

TokenRing

TokenRing

Scalable Network—ExampleScalable Network—Example

• Readdress the network– Each region has its own block of addresses

• Queries bounded by using ip summary-address eigrp command

1.1.2.0

2.2.2.0


Regional Office

Remote Office

Summarized Routes

Summarized RoutesSummarized Routes

Summarized Routes

Summarized Routes Summarized Routes

Tiered Network DesignTiered Network Design

OtherRegions

Core

OtherRegions

OtherRegions

OtherRegions


More EIGRP Scalability RulesMore EIGRP Scalability Rules

• Proper network resources– Sufficient memory on the router– Sufficient bandwidth on WAN interfaces

• Proper configuration of the bandwidth statement over WAN interfaces, especially over Frame Relay


Verifying EIGRP Operation


Verifying EIGRP OperationVerifying EIGRP Operation

show ip protocolsRouter#

show ip route eigrpRouter#

show ip eigrp traffic Router#

show ip eigrp neighborsRouter#

show ip eigrp topologyRouter#

• Displays the neighbors discovered by IP EIGRP

• Displays the IP EIGRP topology table

• Displays current EIGRP entries in the routing table

• Displays the parameters and current state of the active routing protocol process

• Displays the number of IP EIGRP packets sent and received


Verifying EIGRP Operation (cont.)

Verifying EIGRP Operation (cont.)

debug ip eigrp summaryRouter#

debug ip eigrp routeRouter#

show ip eigrp eventsRouter#

debug eigrp packetRouter#

debug eigrp neighborRouter#

• Displays all types of EIGRP packets, both sent and received

• Displays the EIGRP neighbor interaction

• Displays advertisements and changes EIGRP makes to the routing table

• Displays a brief report of the EIGRP routing activity

• Displays the different categories of EIGRP activity, including route calculations


Case Study


Case Study—EIGRPCase Study—EIGRP

Class CClass C

Class BClass B

AutonomousSystem 400

AutonomousSystem 400

Frame RelayNetwork

Frame RelayNetwork

RedundantPVCs to EachRedundant

PVCs to Each

Fast EthernetEthernetSerial

Rest ofCore

Rest ofCore

JKL’s Acquisition DJKL’s Acquisition D 1 Class B - Public 1 Class C - Private1 Class B - Public 1 Class C - Private

HQHQ

Remoteoffices

Remoteoffices

A

B

U

V

G


Lab Exercise


SummarySummary

After completing this chapter, you should be able to perform the following tasks:

• Describe EIGRP features and operation• Explain how EIGRP discovers, chooses, and

maintains routes• Explain how EIGRP supports the use of VLSM• Explain how EIGRP operates in an NBMA

environment• Explain how EIGRP supports the use of route

summarization


Summary (cont.)Summary (cont.)

• Describe how EIGRP supports large networks • Configure EIGRP• Verify EIGRP operation• Given a set of network requirements, configure

an EIGRP environment and verify proper operation (within described guidelines)of your routers

• Given a set of network requirements, configureEIGRP in an NBMA environment andverify proper operation (within described guidelines) of your routers


Review QuestionsReview Questions

1. How are IGRP and EIGRP different in their metric calculation?

2. Why are EIGRP routing updates described as “reliable?”

3. What does it mean when a route is marked as a feasible successor?

4. What is the recommended practice for configuring bandwidth on a Frame Relay point-to-point subinterface?

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