15 Routing Protocols

8/13/2019 15 Routing Protocols

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2008 Cisco Systems, Inc. All rights reserved. Cisco Publ ic 1BRKRST-1301

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IP Routing

Novan Aryandi

[email protected]

Cisco Systems Indonesia
mailto:[email protected]:[email protected]


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To route a router need to know:

Destination addressesSources it can learn from

Possible routes

Best route

Maintain and verify routing information

What is Routing?

172.16.1.010.120.2.0


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What is Routing? (cont.)

NetworkProtocol

DestinationNetwork

ConnectedLearned

10.120.2.0172.16.1.0

ExitInterface

E0S0

Routed Protocol: IP

Routers must learn destinations that are not directlyconnected

172.16.1.010.120.2.0

E0S0


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Static Route

Uses a route that a

network administrator entersinto the router manually

Dynamic Route

Uses a route that a

network routing protocoladjusts automatically fortopology or traffic changes

Identifying Static and Dynamic Routes


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172.16.2.1

SO

Static Routes

172.16.1.0

B172.16.2.2

Network A

Configure unidirectional static routes to and from a stub network toallow communications to occur.

B

Stub Network


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Defines a path to an IP destination network or subnet

Router(config)#ip route network [mask]

{address

|interface

}[distance

] [permanent]

Static Route Configuration


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Stub Network

ip route 172.16.1.0 255.255.255.0 172.16.2.1

172.16.2.1

SO

Static Route Example

172.16.1.0

B172.16.2.2

Network A B

This is a unidirectional route. You must have a route configured in the oppositedirection.



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Stub Network

ip route 0.0.0.0 0.0.0.0 172.16.2.2

Default Routes

172.16.2.1

SO

172.16.1.0

B172.16.2.2

Network A B

This route allows the stub network to reach all known networks beyond router A.



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What is a Routing Protocol?

Routing protocols areused between

routers to determine paths andmaintainrouting tables.

Once the path is determined arouter can route a routedprotocol.

NetworkProtocol

DestinationNetwork

ConnectedRIP

IGRP

10.120.2.0172.16.2.0172.17.3.0

ExitInterface

E0S0S1

Routed Protocol: IPRouting protocol: RIP, IGRP

172.17.3.0

172.16.1.010.120.2.0

E0S0



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Autonomous System 100 Autonomous System 200

IGPs: RIP, IGRP EGPs: BGP

Autonomous Systems: Interior or ExteriorRouting Protocols

An autonomous system is a collection of networks under acommon administrative domain

IGPs operate within an autonomous system

EGPs connect different autonomous systems


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Administrative Distance:Ranking Routes

IGRPAdministrativeDistance=100

Router D

Router BRouter A

Router C

RIPAdministrativeDistance=120

E

I need to send a packet to

Network E. Both router B

and C will get it there.

Which route is best?



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Classes of Routing Protocols

Distance Vector

Hybrid Routing

Link StateC

B

A

D

C

D

B

A



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Distance Vector Routing Protocols

Pass periodic copies of routing table to neighborrouters and accumulate distance vectors

C

D

B

A

C B AD

RoutingTable

RoutingTable

RoutingTable

RoutingTable

Distance

How farVectorIn which direction



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Routers discover the best path to

destinations from each neighbor

A B C

10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0

E0 S0 S0 S1 S0 E0

Routing Table

10.2.0.0

10.3.0.0

0

0

S0

S1

Routing Table

10.3.0.0 S0 0

10.4.0.0 E0 0

Routing Table

10.1.0.0

10.2.0.0

E0

S0

0

0

Distance VectorSources of Information andDiscovering Routes



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A B C

10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0

E0 S0 S0 S1 S0 E0

Routing Table

10.1.0.0

10.2.0.0

10.3.0.0

Routing Table

10.2.0.0

10.3.0.0

10.4.0.0

10.1.0.0

0

0

1

1

S0

S1

S1

S0

Routing Table

10.3.0.0 S0 0

10.4.0.0 E0 0

10.2.0.0 S0 1

E0

S0

S0 1

0

0




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A B C

10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0

E0 S0 S0 S1 S0 E0

Routing Table

10.1.0.0

10.2.0.0

10.3.0.0

10.4.0.0

Routing Table

10.2.0.0

10.3.0.0

10.4.0.0

10.1.0.0

0

0

1

1

S0

S1

S1

S0

Routing Table

10.3.0.0 S0 0

10.4.0.0 E0 0

10.2.0.0 S0

10.1.0.0 S0

1

2

E0

S0

S0

S0

1

2

0

0



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Distance VectorSelecting BestRoute with Metrics

Information used to select the best path for routing

56T1

56

T1Ticks, hop count

B

A

Hop count

IPX

RIP

IGRP

Bandwidth

Delay

Load

Reliability

MTU



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Distance VectorMaintaining RoutingInformation

Updates proceed step-by-stepfrom router to router

A

Process toupdate this

routingtable

Topologychangecausesrouting

tableupdate


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Updates proceed step-by-step

from router to router

A


routingtable

Router A sendsout this updated

routing tableafter the

next periodexpires


tableupdate



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Updates proceed step-by-step

from router to router

AB


routingtable


routingtable


tableupdate

Router A sendsout this updated

routing tableafter the

next periodexpires



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Maintaining Routing InformationProblemRouting Loops

Each node maintains the distance from itself to each possible

destination network

A B C

10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0

E0 S0 S0 S1 S0 E0

Routing Table

10.3.0.0 S0

E0

S0

S0

1

210.1.0.0

10.2.0.0

10.4.0.0

0

0

Routing Table

10.1.0.0 E0

S0

S0

S0

1

210.4.0.0

10.3.0.0

10.2.0.0

0

0

Routing Table

10.2.0.0 S0

S1

S1

S0

1

110.1.0.0

10.4.0.0

10.3.0.0

0

0



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Slow convergence produces inconsistent routing

A B C

10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0

E0 S0 S0 S1 S0 E0X

Routing Table

10.3.0.0 S0

E0

S0

S0

1

210.1.0.0

10.2.0.0

10.4.0.0

0

Down

Routing Table

10.1.0.0 E0

S0

S0

S0

1

210.4.0.0

10.3.0.0

10.2.0.0

0

0

Routing Table

10.2.0.0 S0

S1

S1

S0

1

110.1.0.0

10.4.0.0

10.3.0.0

0

0



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Router C concludes that the best path to network10.4.0.0 is through Router B


A B C

10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0

E0 S0 S0 S1 S0 E0X

Routing Table

10.3.0.0 S0

S0

S0

S0

1

210.1.0.0

10.2.0.0

10.4.0.0

0

2

Routing Table

10.1.0.0 E0

S0

S0

S0

1

210.4.0.0

10.3.0.0

10.2.0.0

0

0

Routing Table

10.2.0.0 S0

S1

S1

S1

1

110.1.0.0

10.4.0.0

10.3.0.0

0

0



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Router A updates its table to reflect the new buterroneous hop count


A B C

10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0

E0 S0 S0 S1 S0 E0X

Routing Table

S0

S0

S0

S0

1

2

10.3.0.0

10.1.0.0

10.2.0.0

10.4.0.0

0

2

Routing Table

E0

S0

S0

S0

1

4

10.1.0.0

10.4.0.0

10.3.0.0

10.2.0.0

0

0

Routing Table

S0

S1

S1

S0

3

1

10.2.0.0

10.1.0.0

10.4.0.0

10.3.0.0

0

0


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Symptom: Counting to Infinity

Packets for network 10.4.0.0 bounce between routers A, B, and C

Hop count for network 10.4.0.0 counts to infinity

A B C

10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0

E0 S0 S0 S1 S0 E0X

Routing Table

10.3.0.0 S0

S0

S0

S0

1

210.1.0.0

10.2.0.0

10.4.0.0

0

4

Routing Table

E0

S0

S0

S0

1

6

10.1.0.0

10.4.0.0

10.3.0.0

10.2.0.0

0

0

Routing Table

S0

S1

S1

S0

5

1

10.2.0.0

10.1.0.0

10.4.0.0

10.3.0.0

0

0


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Solution: Defining a Maximum

Define a limit on the number of hops to prevent infinite loops

A B C

10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0

E0 S0 S0 S1 S0 E0X

Routing Table

10.3.0.0 S0

S0

S0

S0

1

210.1.0.0

10.2.0.0

10.4.0.0

0

16

Routing Table

E0

S0

S0

S0

1

16

10.1.0.0

10.4.0.0

10.3.0.0

10.2.0.0

0

0

Routing Table

S0

S1

S1

S0

16

1

10.2.0.0

10.1.0.0

10.4.0.0

10.3.0.0

0

0


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Solution: Split Horizon

It is never useful to send information about a route back in thedirection from which the original packet came

A B C

10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0

E0 S0 S0 S1 S0 E0X

XX

Routing Table

10.3.0.0 S0

S0

S0

S0

1

210.1.0.0

10.2.0.0

10.4.0.0

0

0

Routing Table

E0

S0

S0

S0

1

2

10.1.0.0

10.4.0.0

10.3.0.0

10.2.0.0

0

0

Routing Table

S0

S1

S1

E1

1

2

10.2.0.0

10.1.0.0

10.4.0.0

10.3.0.0

0

0


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Solution: Route Poisoning

Routers set the distance of routes that have gone down to infinity

A B C

10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0

E0 S0 S0 S1 S0 E0X

Routing Table

10.3.0.0 S0

S0

S0

S0

1

210.1.0.0

10.2.0.0

10.4.0.0

0

Infinity

Routing Table

10.1.0.0 E0

S0

S0

S0

1

210.4.0.0

10.3.0.0

10.2.0.0

0

0

Routing Table

10.2.0.0 S0

S1

S1

E1

1

210.1.0.0

10.4.0.0

10.3.0.0

0

0


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Solution: Poison Reverse

Poison Reverse overrides split horizon

A B C

10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0

E0 S0 S0 S1 S0 E0X

Routing Table

10.3.0.0 S0

S0

S0

S0

1

210.1.0.0

10.2.0.0

10.4.0.0

0

Infinity

Routing Table

10.1.0.0 E0

S0

S0

S0

1

210.4.0.0

10.3.0.0

10.2.0.0

0

0

Routing Table

10.2.0.0 S0

S1

S1

E1

PossiblyDown

210.1.0.0

10.4.0.0

10.3.0.0

0

0

PoisonReverse


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Solution: Hold-Down Timers

Router keeps an entry for the network possibly down state, allowingtime for other routers to recompute for this topology change

Network 10.4.0.0 is down

then back upthen back down

Update afterhold-down Time

Network 10.4.0.0is unreachable

A B C

10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0

E0 S0 S0 S1 S0 E0 XUpdate after

hold-down Time


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Solution: Triggered Updates

Router sends updates when a change in its routing table occurs

A B C

10.2.0.0 10.3.0.0 10.4.0.0

E0 S0 S0 S1 S0 E0 X




10.1.0.0


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RIP Timers

1. Update Timer Broadcast the routing table to all itneighbour for every 30 seconds.

2. Invalidation Timer It is either 3 or 6 times the UpdateTimer. If no updates are received for a particular route andthat route is marked as Invalid route.

3. Holddown Timer The Invalid route is not removed fromthe routing table it will be marked as possibly down onthe routing table. If it receives the route with the bettermetric before the hold down timer expiry then it will acceptor it will remove.


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Share attributes of both distance-vectorand link-state routing

Hybrid Routing

Choose arouting path basedon distance vectors

Converge rapidly usingchange-based

updates

Balanced Hybrid Routing


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Router configuration

Select routing protocols

Specify networks or interfaces Network160.89.0.0

Network 172.30.0.0

IGRP,RIP

Network 172.16.0.0

RIP

RIP

IGRP

IP RoutingConfiguration Tasks


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Defines an IP routing protocol

Router(config)#routerprotocol [keyword]

Mandatory configuration command for eachIP routing process

Identifies the physically connected networkthat routing updates are forwarded to

Router(config-router)#network network-number

Dynamic Routing Configuration


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19.2 kbps

T1

T1 T1

Hop count metric selects the path

Routes update every 30 seconds

RIP Overview


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Starts the RIP routing process

Router(config)#router rip

Router(config-router)#network network-number

Selects participating attached networks

The network number must be a major classful

network number

RIP Configuration


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2.3.0.0router rip

network 172.16.0.0

network 10.0.0.0

RIP Configuration Example

router rip

network 10.0.0.0

2.3.0.0router rip

network 192.168.1.0

network 10.0.0.0

172.16.1.1

S2E0 S3

192.168.1.110.1.1.1 10.2.2.210.1.1.2

S2 S3

10.2.2.3

172.16.1.0 A B C 192.168.1.0

E0


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Verifying the Routing ProtocolRIP

RouterA#sh ip protocolsRouting Protocol is "rip"

Sending updates every 30 seconds, next due in 0 seconds

Invalid after 180 seconds, hold down 180, flushed after 240

Outgoing update filter list for all interfaces is

Incoming update filter list for all interfaces is

Redistributing: rip

Default version control: send version 1, receive any version

Interface Send Recv Key-chain

Ethernet0 1 1 2Serial2 1 1 2

Routing for Networks:

10.0.0.0

172.16.0.0

Routing Information Sources:

Gateway Distance Last Update

10.1.1.2 120 00:00:10

Distance: (default is 120)

172.16.1.1

S2E0 S3

192.168.1.110.1.1.1 10.2.2.210.1.1.2

S2 S3

10.2.2.3

172.16.1.0 A B C 192.168.1.0

E0

Di l i th


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Displaying theIP Routing Table

RouterA#sh ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B -BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate

default

U - per-user static route, o - ODR

T - traffic engineered route

Gateway of last resort is not set

172.16.0.0/24 is subnetted, 1 subnets

C 172.16.1.0 is directly connected, Ethernet0

10.0.0.0/24 is subnetted, 2 subnets

R 10.2.2.0 [120/1] via 10.1.1.2, 00:00:07, Serial2

C 10.1.1.0 is directly connected, Serial2

R 192.168.1.0/24 [120/2] via 10.1.1.2, 00:00:07, Serial2

172.16.1.1

S2E0 S3

192.168.1.110.1.1.1 10.2.2.210.1.1.2

S2 S3

10.2.2.3

172.16.1.0 A B C 192.168.1.0

E0


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debug ip r ipCommand

RouterA#debug ip ripRIP protocol debugging is on

RouterA#

00:06:24: RIP: received v1 update from 10.1.1.2 on Serial2

00:06:24: 10.2.2.0 in 1 hops

00:06:24: 192.168.1.0 in 2 hops

00:06:33: RIP: sending v1 update to 255.255.255.255 via

Ethernet0 (172.16.1.1)

00:06:34: network 10.0.0.0, metric 1

00:06:34: network 192.168.1.0, metric 3

00:06:34: RIP: sending v1 update to 255.255.255.255 via

Serial2 (10.1.1.1)

00:06:34: network 172.16.0.0, metric 1

172.16.1.1

S2E0 S3

192.168.1.110.1.1.1 10.2.2.210.1.1.2

S2 S3

10.2.2.3

172.16.1.0 A B C 192.168.1.0

E0


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Introduction to OSPF

Open Standard

Link State Protocol, Uses SPF algorithm

Fast Convergence with triggered updates

Classless protocol, supports VLSM and summarization

Uses Cost as metric (Inverse Bandwidth)

Area 1

Area 0

Area 2


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Link-State Routing Protocols

After initial flood, pass small event-triggered link-stateupdates to all other routers

Link-State Packets

SPFAlgorithm

TopologicalDatabase

Shortest Path First Tree

RoutingTable

C A

D

B


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Shortest Path Algorithm

The best path is the lowest-cost path.


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g

OSPF Terminology


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Steps in the Operation of OSPF


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Hello Protocol

It is the means by which neighbors are discovered. It advertises several parameters on which two routers must agree before they can become

neighbors.

Hello packets act as keepalives between neighbors.

It ensures bi-directional communication between neighbors.

It elects Designated Routers (DRs) and Backup Designated Routers (BDRs) on Broadcastand Nonbroadcast Multiaccess (NBMA) networks.


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Establishing Adjacency


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OSPF Network Types


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DR and BDR Election Process

Router with highest

priority

In case of tie, router

with highest router ID


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Hierarchical Design (Areas)

OSPF supports two important concepts: autonomous systems and areas.

Within an AS, areas are used to provide hierarchical routing.

An areais a logical grouping of OSPF routers and links that effectively divide an OSPF

domain into sub-domains

Areas are used to control when and how much routing information is shared across yournetwork.

OSPF implements a two-layer hierarchy: the backbone (area 0) and areas off of

the backbone (areas 165,535)

Every area off the backbone must be connected to the backbone area.


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OSPF CONFIGURATION

Configuring the OSPF


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Configuring the OSPFRouting Process

Configuring OSPF Loopback Address


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Configuring OSPF Loopback Addressand Router Priority

M dif i OSPF C t M t i


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Modifying OSPF Cost Metric


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Configuring OSPF Timers

Common OSPF


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Common OSPFConfiguration Issues

V if i OSPF C fi ti


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Verifying OSPF Configuration

show ip protocol

show ip route

show ip ospf interface

shop ip ospf

show ip ospf neighbor detail

show ip ospf database


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EIGRP

Characterstic of EIGRP

1. Cisco properitary.

2. Advanced Distance vector protocol.

3. Claless routing protocol.

4. Multiple network layer protocol support using PDM.

5. Faster convergence.

6. Equal and Unequal cost path load balancing.

7. Manual summarization at Interface level.

8. Bandwidth usage control for routing updates.


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Share attributes of both distance-vector

and link-state routing

Hybrid Routing

Choose arouting path basedon distance vectors

Converge rapidly usingchange-based

updates

Balanced Hybrid Routing


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Process and Techniques

1. Efficient Neighbour Discovery.

2. It uses RTP for its updates.

3. DUAL Finite state Machine.

4. Protocol Dependent Module


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Three Tables Maintained by EIGRP

1. Neighbour table.

2. Topology table.

3. Routing table.


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Terms Used by Eigrp

1. Successor route

The Efficient and Loop free path with thelowest FD.

2. Feasible Distance The Distance between the local router andthe Destination Network.

3. Advertise Distance The Distance between the Next hop router

and the destination.4. Successor Next Hop Router of the Best path.

5. Feasible Successor Next Hop router fo the backup path forthe Best route.


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Condition for Feasible successor

AD of the considered backup route < FD of thesucessor route.


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More Info

Topology table will have a maximum of six backuppath for a successor route. It is for faster convergence.

Active State - Recomputation

Passive state No Re-computation


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EIGRP packet types

1. Hello2. Update

3. Query

4. Reply5. Ack

6. Note: 224.0.0.10 is the multicast address used byEIGRP packet types (Hello, Update and Query

Packet)


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Conditions to Establish Neighbour Adjacency

1. Identical K Metrics

2. Same AS.


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EIGRP Metric parameters

1. Bandwidth

2. Load

3. Delay

4. Reliability

5. MTU

6. Note: Eigrp Metric = IGRP Metric * 256.

7. Eigrp Metric 32 bit

8. Igrp Metric 24 bit


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Basic configuration

Conf t)#router eigrp

-rtr)#network


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Load Balancing

Eigrp supports Equal cost path load balancing. Defaultis 4 and Maximum is 6.

It also supports Unequal cost path load balancing usingVariance command.


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Useful show commands for EIGRP

Sh ip eigrp neighbour

Sh ip eigrp topology

Sh ip route eigrp

Sh ip protocols.


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Summary

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

Determine when to use a static or dynamic route.

Configure a static route on a Cisco Router.

Describe how distance vector routing protocols operate.

Configure the RIP and OSPF routing protocols on a Cisco router.

Use show ip route, show ip protocols, and other show and debugcommands to verify proper routing operation.


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Documents

15 Routing Protocols