ccnp route guide

8/20/2019 CCNP Route Guide

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Welcome to your Bulldog Study

Guide for the CCNP ROUTE exam!

I know you’re anxious to ge

started, so I’ll keep this short…

Your CCNP ROUTE exam preprequires you to tackle some

complex subjects, with BGP,

multiarea OSPF, and routeredistribution among them. In this

guide, you’ll find clear and

comprehensive explanations for each and every one of these topics,

along with hundreds of illustrations

and configs from live Cisco routers.


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(I do not use simulators in my books

or videos.)

Speaking of videos, I’ve added a

special feature to this ebook that’s

guaranteed to help you master these

complex concepts.

And just as exciting, these features

don’t cost anything!

At the end of each section, you’ll

find links to videos on my YouTubecomputer certification video

training channel that are related to

the topic you just studied.


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You’ll find Video Practice Exams,

5-minute Video Boot Camps, and

other video types - all of whicwill help you nail this difficul

exam.

You’ll also find links to my free

CCNP ROUTE Video Boot Camp

on route redistribution and OSPF

stub areas, and my full 22-hour CCNP ROUTE Video Boot Camp,

available on both DVD and i

downloadable format.

That last one’s not quite free, but i

a world of $500 video courses,you’ll find the price to be quite


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refreshing.

I also invite you to join me o

Twitter, Facebook, LinkedIn, and

other social media sites. I’m there

live every day and happy to cha

with you there!

‘Nuff said! Let’s get started …

… and as always, thanks for makin

TBA part of your CCNP success

story!

Chris Bryant

CCIE #12933

“The Computer Certification


6/1409

Bulldog”

Chris Bryant

CCIE #12933

“The Computer Certification

Bulldog”

[email protected]

Website:

http://www.thebryantadvantage.co

Twitter:

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Facebook: http://on.fb.me/gPq52d

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YouTube:

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Free Resources To Help You

Pass The CCNP ROUTE

Exam!

In addition to this information-

packed CCNP ROUTE Study

Guide, TBA has literally dozens o

additional practice exams, VideoBoot Camps, and illustrated

tutorials to help you destroy this

exam!

First, for some videos!

My YouTube Computer


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Certification Channel has quite a

few videos on the CCNP ROUTE

exam:


I hope you’ll click “subscribe”while you’re out there - I’m addin

new videos AND certifications on a

regular basis, including Security+,etwork+, and a new CCNA

Security course in 2012!

You’ll also find links to individual

videos on that channel at the end o

most chapters of this ebook.



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I have a separate Videos &

Tutorials page on my website for

each of the CCNP exams - here’sthe page dedicated to ROUTE:


Be sure to scroll ALL the way

down that page - there are links to

practice exams, tutorials, and VideoBoot Camps!

For future reference, or for review,here are my pages for the SWITCH

and TSHOOT exams:

SWITCH:

http://www.thebryantadvantage.com/CCNPCertificationROUTEExam642902Tutorials.htm


11/1409


TSHOOT:


I also have a Video Boot Camp

hosted on Udemy.com -- well,

actually, two of them!

The first is 100% free and is a

tremendous lab and lecture on route

redistribution and multiarea OSPF.

This is must-see material, my

friends… and you can watch i

online, or you can download it - or

both!

http://udemy.com/http://www.thebryantadvantage.com/CCNPCertificationTSHOOTExam642832Tutorials.htmhttp://www.thebryantadvantage.com/CCNPCertificationSWITCHExam642813Test.htm


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http://www.udemy.com/ccnp-route-

boot-camp-redistribution-and-ospf-

stub-areas/

There’s also a full hour-lon

preview from my CCNP ROUTEDVD on that site:

http://www.udemy.com/ccnp-route-on-demand-video-boot-camp/

And should you choose to enroll i

that course OR get the DVD, please

remember to use this link and save

yourself $10!

http://www.udemy.com/ccnp-route-on-demand-video-boot-camp/http://www.udemy.com/ccnp-route-boot-camp-redistribution-and-ospf-stub-areas/


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When I post new videos or tutorials, or whenever there’s

important news in the computer

certification world, I always post ion our Facebook and Twitter feeds

as well as the Bulldog Blog.

I urge you to click these links and

oin us!

We have some great conversations

and the occasional giveaway ou

there -- and if you have a questioor comment, just send it via Twitter

http://www.thebryantadvantage.com/CCNPROUTEStudyGuideUpgrade.htm


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or leave it on Facebook! I’

always happy to hear from you!

Twitter:

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Facebook: http://on.fb.me/gPq52d

Bulldog Blog:

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The CCNP ROUTE exam is a toug

one. Use all of these resources iaddition to this study guide - and

thanks for making TBA part of your

CCNP success story!

http://thebryantadvantage.blogspot.com/http://on.fb.me/gPq52dhttp://www.twitter.com/ccie12933


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Chris Bryant

CCIE #12933

“The Computer Certificatio

Bulldog”

Copyright © 2012 The Bryant Advantage.All Rights Reserved.


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Dedication

For Suzy and Squeaky

Always loved, never forgotten.


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Copyright © 2012 The Bryant Advantage.

All Rights Reserved.


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There’s only one way

to get my crystal-clear CCNP ROUTE Video

Boot Camp instruction

--

-- and that’s directlyfrom TBA.

All of my Video

Boot Camp DVDs give

you a full, free HOUR


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of training to let you

“Try Before You Buy”!

It’s this sweet and simple:

My CCNP Bulldog Boot Camps

DVDs have helped network admins

around the world - from the UK toAustralia, from Russia to the US -

become CCNPs.

o other DVD offers my crystal-

clear and concise instruction - and I

never use simulators in my labs.

And I don’t charge you an arm and a


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leg for a DVD.

Even better - you can save $10 o

any DVD or Bulldog DVD Bundle

by following this link:


I know you’ll be happy with any

and all of my Video Boot CampDVDs.

You have my word and my name oit.

Chris Bryant

CCIE #12933

“The Computer Certificatio

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Bulldog”


http://www.thebryantadvantage.com/


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Copyright Information:

Cisco®, Cisco® Systems, CCIE™,CCNP, CCNA, Cisco Certified

etwork Administrator, Cisco

Certified Network Professional,and Cisco Certified Internetwor

Expert are registered trademarks o

Cisco® Systems, Inc., and/or itsaffiliates in the U.S. and certai

countries.

All other products and company

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registered trademarks, and servicemarks of the respective owners.


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Throughout this Study Guide, The

Bryant Advantage has used its bes

efforts to distinguish proprietarytrademarks from descriptive names

by following the capitalizatio

styles used by the manufacturer.

Disclaimer:

This publication, The Bryant dvantage CCNP ROUTE Study

Guide, is designed and intended to

assist candidates in preparation for the CCNP ROUTE exam for the

Cisco Certified Networ

Professional ® certification.


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All efforts have been made by the

author to make this book as accurate

and complete as possible, but noguarantee, warranty, or fitness are

implied, expressly or implicitly.

The enclosed material is presented

on an “as is” basis.

either the author, The Bryan

Advantage, Incorporated, or theparent company assume any

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information contained in this

workbook.


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This Course Guide is an original

work by the Author. Any

similarities between materialspresented in this Study Guide and

actual CCNP® exam questions are

completely coincidental.

Copyright 2012 © The Bryan

Advantage




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Table Of Contents

Introduction:

Free Resources For TheCCNP ROUTE Exam:

Dedication:

DVD Discount Offer:

Legal Notices:

IP Routing Fundamentals:


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EIGRP Fundamentals:

EIGRP Intermediate and

Advanced Skills:

Link State Protocols And

Single-Area OSPF:

Multi-Area OSPF And

OSPF Route Redistribution:

BGP:

Remote Workplace: VPNs

and IPSec:

Remote Workplace, Part II:


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IP Version 6:

Route Redistribution:

Bonus Section: Creating A

VLSM Scheme:

More VLSM!:


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IP Routing Fundamentals

Okay, I know what you’re thinking!

“I’m a CCNA already, I already

studied RIP, I know all the DistanceVector stuff, I know my admi

distances. Let’s get to the new

stuff!”

Before we do that, we’re going to

take some time to review andmaster some fundamental routin

skills …

… because without that mastery, we


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can’t become truly great.

And while I know you’re familiar

with these protocols, this chapter is

going to be more than a review for

you - it’s going to sharpen your

skills with these critical protocols

to the point where the CCNP

ROUTE questions will be child’s

play for you.

There’s also more than a little

material in this section that willhelp you big time on your CCNP

TSHOOT exam as well.

Sooooo…..


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Let’s get started!

ow and Where Distance Vector

rotocols Operate

Typically, distance vector protocols

are used on Local Area Networks(LANs). While DV protocols wor

well in smaller and more stable

environments, they have severaldrawbacks that prevent them fro

being used as Wide Area Networ

(WAN) protocols.

One drawback is that RIP

broadcasts routing updates every 30seconds, as illustrated by show ip


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rotocols:

R5#show ip protocols

Routing Protocol is “rip”

Sending updates every 30 seconds, next

due in 16 seconds Invalid after 180

seconds, hold down 180, flushed after 240

RIPv1 will broadcast full routin

tables as the update, regardless o

whether anything has actually

changed since the last update. This

is a waste of bandwidth and

resources, since your average

LAN’s subnets aren’t going to

change every minute. (We hope!)


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RIPv2 multicasts updates to

224.0.0.9 rather than broadcastin

them, but the updates are still senout every 30 seconds.

In a larger network, another

problem arises. RIP routing updates

can hold a maximum of 25 routes,

so if there are 105 routes in your

network, five separate updatepackets would be needed. Since

these updates would go out every

30 seconds, whether anything hadactually changed in the network,

RIP is generally a poor choice for a

WAN protocol.


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Remember, everything we do on a

router has a cost to that router and

others - a cost in CPU, bandwidth,and time. Those continual RIP

updates have a high cost and very

little value.

Drawback 2: RIPv1 is a classful

routing protocol, and therefore does

not support VLSM. The only masksRIPv1 understands are the classful

masks for Class A (255.0.0.0),

Class B (255.255.0.0), and Class C(255.255.255.0).

Drawback 3: Both versions of RIPonly understand hop count -


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literally, how many “hops” there

are from Point A to Point B. On a

LAN, this really isn’t a problem,but RIP’s limitations quickly

become a problem on a WAN.

There are two paths between A and

B. The path using the two T1 linesis much faster than the 56 kbps path,


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but RIP will see these paths as

equals. RIP’s routing algorithm, the

ellman-Ford algorithm, considersonly hop count in computing its

metric.

In this example, RIP will the

perform equal-cost load balancin

over the two links. (DV protocols

perform equal-cost load balancinover four paths by default.)

efault DV Protocol Behaviors

DV protocols do have some

drawbacks, but they also have somedefault behaviors that help preven


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routing loops. You saw all of these

in your CCNA studies, but let’s do a

quick review.

Split Horizon simply means that a

routing protocol cannot advertise a

route via the same interface upo

which it was learned. Here, Router

3 cannot advertise the loopbac

network 2.0.0.0 via its etherneinterface, because that is the

interface upon which the router firs

learned about the network.


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oison Reverse allows a router to

advertise a network with an metric

of “unreachable” when that networ

becomes unavailable. This allows

the other routers to learn that the

network is unreachable much faster

than if it were left up to the normal

DV protocol behaviors -- and i

turn, that results in fewer misrouted

/ lost packets.


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It’s obviously in our best interest to

have the quickest convergence time

possible. If some routers thin

“network A” is available and othersthink the network is unavailable,

routing for that network is going to

be substandard at best and routinloops can easily form.


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The Basics Of RIPv1, RIPv2, an

IGRP

RIPv1:

Broadcasts updates every 30

seconds

Classful, does not recognizeVLSM, update carries entire

routing table

Uses Bellman-Ford algorithm

Equal-cost load shares by


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default, max hop count is 15

No routing updateauthentication available

Updates carry 25 routes max

RIPv2:

Multicasts updates every 30

seconds to 224.0.0.9

Classless, supports VLSM,update carries entire routing


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table

Uses Bellman-Ford anddefault equal-cost load

sharing, max hop count is 15,

updates carry 25 routes max

Supports routing updateauthentication (clear-text and

MD5)

EIGRP:

Multicasts to 224.0.0.10


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Sends entire routing table only

when the adjacency is first

formed

Sends only routing update after

that when necessary, updatereflects only the changes

Uses DUAL routing algorithm

Equal-cost load sharing by

default, unequal-cost load

sharing configured with the

variance command


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EIGRP is not a pure distance-vector

protocol, but I’ve put it here for

easy comparison to RIP. I alsodidn’t go into a discussion o

EIGRP here, since we’ll be doin

lenty of that later in the course.

The Role Of Administrative

istance

When a route lookup is performed

in a routing table, there may bemore than one path that meets the

criteria for being selected.

Basically, there is a four-stepprocess a router goes through whe


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looking for the best route to use:

1. If there are multiple routes

to a destination, the route with

the longest prefix length is

used.


to a destination and they havethe same prefix length, the

route with the lowest

administrative distance isused.


with the same prefix length and


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AD, the route with the lowest

metric is used.


with the same prefix length,

AD, and metric, all of theseroutes will be used in load

balancing as allowed by the

protocol.

Consider a router that is lookinthrough its routing table to decide

the next-hop IP address to use to

reach the destination 222.1.3.1.

I’m going to use IGRP in this


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example, but please note that IGRP

is obsolete and is no longer tested

on Cisco certification exams.

In the unlikely but possible

circumstance that the router has one

path discovered by OSPF and

another by IGRP, the two paths

could look like this:

O: 222.1.3.0 /25 via 172.1.1.2, serial1

I: 222.1.3.0 /24 via 175.1.1.2, serial0

In this case, the OSPF route would

be chosen, because it is the longes

match; its mask is /25, a longer match than IGRP’s classful mask o


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/24. The administrative distance

(AD) does not come into use. Bu

what if the masks were the exacsame length?

O: 222.1.3.0 /24 via 172.1.1.2, serial1

I: 222.1.3.0 /24 via 175.1.1.2, serial0

A tiebreaker is needed, and that’s

where the AD comes in. The pat

discovered by the protocol with the

lowest AD will be used. Since

IGRP’s AD is 100 and OSPF’s is

110, the IGRP path will actually be

used over the OSPF path.


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AD values to know:

Directly connected route /

Static route using exit

interface: 0

Static route with next-hop IP

address: 1

EIGRP Summary: 5 (if you

know where to look -- more o

that later)

External BGP: 20


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Internal EIGRP: 90

OSPF: 110

RIP: 120

External EIGRP: 170

Internal BGP: 200

Unknown network: 255

You may notice some differences


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here from the ADs you learned i

earning your CCNA. There are now

two kinds of non-summary EIGRProutes listed, internal and external.

Much more about those route types

in the EIGRP sessions.

outing Table Operation

This entire operation is practicallytransparent to you and I as networ

admins, and that’s fine when things

go as we expect.

When things don’t go as we expect -

and when we’re studying for Ciscoexams! -- we better know the


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“hows” and “whys” of the routin

table.

We love it when the router has

multiple paths to a given network!

That way, if we lose one path, we

have another - and we’ll take all the

redundancy we can get in today’s

delay-sensitive networks.

ow that we know how a routin

table is built, let’s take a closer

look at a small table and identifythe different values.

R1#show ip route

Codes: C - connected, S - static, I - IGRP, R -

RIP, M - mobile, B - BGP


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D - EIGRP, EX - EIGRP external, O -

OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 -

OSPF NSSA external type 2E1 - OSPF external type 1, E2 - OSPF

external type 2, E - EGP

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS

level-2, ia - IS-IS inter area

* - candidate default, U - per-user static

route, o - ODR

P - periodic downloaded static route

Gateway of last resort is not set

172.12.0.0/16 is variably subnetted, 2

subnets, 2 masks

R 172.12.23.0/27 [120/1] via

172.12.123.2, 00:00:01, Serial0

[120/1] via

172.12.123.3, 00:00:04, Serial0

C 172.12.123.0/24 is directly

connected, Serial0


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10.0.0.0/24 is subnetted, 1 subnets

C 10.1.1.0 is directly connected,

Ethernet0

There is one RIP route and two

directly connected routes. Since

we’re primarily interested in the

RIP route for this discussion, we’ll

run show ip route rip to see only

the routes that RIP has discovered.

R1#show ip route rip


subnets, 2 masks

R R 172.12.23.0/27 [120/1] via

172.12.123.2, 00:00:04, Serial0

[120/1] via

172.12.123.3, 00:00:04, Serial0


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The network 172.12.23.0/27 is the

destination. The numbers contained

in the brackets are theadministrative distance of the

protocol that discovered the route,

followed by the metric for that path.

Since this is a RIP route, the metric

shown is the number of hops to tha

network.

The IP addresses following the

word “via” are the next-hop IP

addresses, followed by the time thisroute was last refreshed. Since RIP

sends full routing updates every 30

seconds regardless of version, thisvalue will not exceed 30 seconds


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for a valid RIP route unless the

holddown timers are in use.

Finally, each line ends by naming a

interface. This is the local interface

that data sent to this destination will

use to exit the router. It has nothin

to do with the downstream router.

In this example, we have twoseparate paths listed for a single

destination. Remember the process

a router uses to determine the bespath? It’s worth repeating….

The route with the longest prefix length will be selected.


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The term “longest prefix

match” refers to the length of

the subnet mask.

If there are multiple routes

with the same prefix length, theroute with the lowest

administrative distance will be

used. Generally referred to as“AD”, this is a measurement o

a protocol’s believability. The

lower the AD, the more believable the protocol.

If there are multiple routes


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with the same prefix length and

AD, the route with the lowest

metric will be preferred.

Finally, if the preceding three

values are all equal, equal-cost load sharing will be put

into action.

The prefix length, administrative

distance, and metrics are all thesame. Therefore, RIP will use bot

paths via equal-cost load sharing.

You can verify that load sharing isin operation (and a lot of other


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things!) by running show ip

rotocols.

In this example, we can also see

when the next routing update is

expected, what version of RIP

you’re running, whether routin

updates are being authenticated

(you would see a value under “Key-

chain” if authentication was in use),and whether autosummarization is

on or off.

R1#show ip protocols

Routing Protocol is “rip”

Sending updates every 30 seconds, next

due in 7 secondsInvalid after 180 seconds, hold down 180,

flushed after 240


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Outgoing update filter list for all interfaces is

not set

Incoming update filter list for all interfaces is

not setRedistributing: rip

Default version control: send version 2,

receive version 2

Interface Send

Serial0 2

Automatic network summarization is notin effect (autosummarization has been turned

off)

Maximum path: 4

Routing for Networks: 172.12.0.0

Routing Information Sources:

Gateway Distance172.12.123.3 120


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172.12.123.2 120Distance: (default is 120)

As great as dynamic routin

protocols are, I can guarantee yo

that the time will come when yoneed to use a routing method tha

has less overhead. Maybe you’re

working with a router with verylimited resources; maybe you wan

to have more personal control abou

routing operations. There areseveral methods you can use i

these scenarios, and the mos

common are static routes anddefault static routes.


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tatic Routing

Routing protocols are much more

effective in keeping an accurate

routing table, and adapt to networ

changes much more quickly tha

static routing - and it takes a lot less

of our time, too.

So why use static routing at all?

If a route has one IP address as the

next-hop address for every singleroute in its table, why keep a full

dynamic routing table when a single

static default route will do?


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As we’ll see in the Advanced

EIGRP and especially the multiarea

OSPF sections, this strategy isactually built in to these dynamic

routing protocols.

Static routes can also serve as a

tourniquet of sorts for your network.

If something goes wrong with your

dynamic protocol and you need togive your users a quick path to a

gateway that can get them where

they need to go, a quick static routecan give you (some) peace and

quiet while you fix the problem.

A static route can also serve as a


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backup to a dynamic routin

protocols - a floating static route,

that is.

A floating static route is assigned a

administrative distance higher tha

that of any dynamic protocol

running on the router, ensuring tha

the only way the static route can be

used is if all dynamic routes leavethe table.

A default static route serves as arouter’s gateway of last resort.

Remember that a default static route

isn’t the path packets will take first,it’s the path they’ll take if there is


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no other match in the routing table

at all.

You learned how to configure a

static route in your CCNA studies,

but let’s quickly review the syntax:

R1(config)#ip route 3.3.3.3 255.255.255.255

172.12.123.3

R1(config)#ip route 3.3.3.3 255.255.255.255

serial0

These two static routes are bot

host routes; that is, they are valid

for only one destination, in this case

3.3.3.3 /32. Note that the mask is a

subnet mask, not a wildcard mask.


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In the first example, the IP address

at the end of the static route is the

next-hop IP address for the route. Ithe second, the interface named a

the end of the static route is the

local exit interface.

You will never configure a static

route that uses a local IP address or

a remote interface name.

You’ll use the ip route command for

a default static route, but the IPaddress and mask look rather odd:

R1(config)#ip route 0.0.0.0 0.0.0.0 172.12.123.3

R1#show ip route


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< code table removed for clarity >

Gateway of last resort is 172.12.123.3 to

network 0.0.0.0


subnets, 2 masks

R 172.12.23.0/27 [120/1] via172.12.123.2, 00:00:14, Serial0

[120/1] via

172.12.123.3, 00:00:26, Serial0

C 172.12.123.0/24 is directlyconnected, Serial0


C 10.1.1.0 is directly connected, Ethernet0

S* 0.0.0.0/0 [1/0] via 172.12.123.3

The ip route statement contains all

zeroes for both the destination and

mask. The gateway of last resort isnow set, and any data that does no


68/1409

have a match in the routing table

will be sent to the next-hop address

172.12.123.3. The asterisk next tothe S indicates that this is a defaul

route.

The ip route statement for a defaul

route can also end with the local

exit interface:

R1(config)#ip route 0.0.0.0 0.0.0.0 serial0

R1#show ip route


Gateway of last resort is 0.0.0.0 to network

0.0.0.0



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subnets, 2 masks

R 172.12.23.0/27 [120/1] via

172.12.123.2, 00:00:26, Serial0

[120/1] via172.12.123.3, 00:00:08, Serial0

C 172.12.123.0/24 is directly

connected, Serial0


C 10.1.1.0 is directly connected, Ethernet0

S* 0.0.0.0/0 is directly connected, Serial0

R1#

While the gateway is now set to

0.0.0.0 rather than 172.12.123.3,

the net effect is the same. Ipersonally like to configure a

default static route with a specified

next-hop address, but it’s up to theindividual.


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Floating Static Routes In Action

In this lab and all others in the

course, all IP addresses end witthe router’s number. For example,

R1’s Serial0 interface on the

172.12.123.0 /24 network has an IPaddress of 172.12.123.1.

ote that RIP is not running over theentire network -- it’s not runnin

over the serial link connecting R1

and R3’s serial1 interfaces.

R1/R2/R3 Frame Network:


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172.12.123.0 /24

R1 / R3 Serial Connection:

210.1.1.0 /24

R2 / R3 Ethernet Network:

172.12.23.0 /27


72/1409

You might be wondering if there

will ever actually be a situatio

where you wouldn’t run a dynamicprotocol over that link. If you’re


73/1409

like me, you’re thinking “Why

wouldn’t I just run RIP over the lin

and let the protocol figure all of thisout?”

Ordinarily we’d be happy to do

that, but in this case we’re bein

asked not to use the S1 link unless

the S0 link goes down. Tha

happens more often than you mighthink, for these reasons…

Bandwidth availability througthe S0 link is much higher than

that of the S1 link, but RIP will

see them as equal


74/1409

Perhaps the S1 link flaps on

occasion and the S0 link is

considered to be much morestable

Perhaps the client just doesn’twant to listen to reason and

just doesn’t want to use that

link and just doesn’t want tohear anything about it (this

happens on occasion, too)

ow let’s hit this lab!

R1 has two next-hop addresses for

the 172.12.23.0 /27 network:


75/1409



subnets, 2 masks

R 172.12.23.0/27 [120/1] via172.12.123.2, 00:00:04, Serial0

[120/1] via

172.12.123.3, 00:00:04, Serial0

We need a static route that will

appear in the routing table only i

those RIP links are gone, but we

also know the AD of a static route

is much lower than that of a RIP-

discovered route.

Here’s how we fix that:

R1(config)#ip route 172.12.23.0

255.255.255.224 210.1.1.3 ?


76/1409

Distan

metric forroute

nameSpecif

name of thnext hop

permanent perma

route

tagSet tag

this route

R1(config)#ip route 172.12.23.0255.255.255.224 210.1.1.3 200

Using the option to change the static

route’s administrative distance

(that’s what “distance metric for


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this route” refers to) creates the

static route with an AD of 200. I

this case, anything higher than 120will do.

We hope. Let’s check it out….

R1#show ip route



subnets, 2 masks

C 172.12.13.0/24 is directly connected,

Serial1

R 172.12.23.0/27 [120/1] via172.12.123.2, 00:00:21, Serial0

[120/1] via

172.12.123.3, 00:00:05, Serial0




78/1409


Ethernet0

ow we need to test the config, andsince we’re in a lab environment,

we’ll close S0 and cut off the RIP

updates. The result:

R1#show ip route



S 172.12.23.0 [200/0] via 210.1.1.3


C 10.1.1.0 is directly connected,Ethernet0

C 210.1.1.0/24 is directly connected, Serial1

R1#ping 172.12.23.3

Type escape sequence to abort.


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Sending 5, 100-byte ICMP Echos to 172.12.23.3,

timeout is 2 seconds: !!!!!

Success rate is 100 percent (5/5), round-trip

min/avg/max = 36/36/36 ms

When we reopen R1’s S0 interface,

the RIP updates will again be

received by R1 and the floatin

static route will be removed fro

the table due to its higher AD.

R1(config)#int s0

R1(config-if)#no shutdown

R1#show ip route< code table removed for clarity >


subnets, 2 masks

R 172.12.23.0/27 [120/1] via


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172.12.123.2, 00:00:17, Serial0

[120/1] via

172.12.123.3, 00:00:00, Serial0




Ethernet0

C 210.1.1.0/24 is directly connected, Serial1

On-Demand Routing (ODR)

In today’s world, the phrase “On-

Demand” brings to mind the latesin technology, where you can watc

anything from my Cisco

certification video training to the

latest episode of Pawn Stars or

arking Wars anytime you like wit


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the push of a button or the click of a

mouse.

The latest and greatest i

technology, right?

Right! Except for “On-DemandRouting” (ODR). ODR can come i

handy for one major reason:

Everything we do on a Cisco

router or switch has a cost, in

the form of CPU, bandwidth,and / or time.

This is especially true of dynamic

routing protocols, so in small


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networks with routers that don’

have resources to spare, static

routing can be beneficial.

In a larger network, though, there is

the need for a middle ground

between static routing and running a

dynamic routing protocol. In Cisco,

this is ODR.

Why just Cisco? Because ODR uses

our old friend Cisco Discovery

Protocol (CDP). As you well know,CDP is Cisco-proprietary, so if we

have a multivendor environment,

ODR is not a viable solution.


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Make sure your ODR routers are

running CDP with show cdp.

On top of that, ODR is designed for

use only in a hub-and-spoke

network. If you have such a networ

and the bandwidth is limited, OD

may be an appropriate solution.

ODR also supports VLSM.

The spokes are going to use ODR to

send directly connected networ

prefixes to the hub. The spoke willuse the IP address of the hub on the

common link as its default gateway.

By using only a single default route,the spoke routers conserve their


84/1409

resources.

ropagating A Default Route

With RIP, IGRP, And No I

outing

When it comes to default routing,

you’ve got three choices:

Use the ip route command

with all zeroes for the

destination address and subne

mask

Use the ip default-networ

command

Use the ip default-gateway


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command

You’ve got the ip route command

down cold at this point, so let’s take

a closer look at ip default-network .

We’ll use the following network.The common subnet is 172.12.123.0

/24. We want R1 to advertise its

directly connected networ 100.1.1.0 /24 to R2 and R3 as a

default route.


86/1409

The ip default-network command is

used to flag a network as a

candidate default route. The routersare already running RIP over the


87/1409

common subnet. R1 will now

introduce 100.1.1.0 /24 as the

default network.R1(config)#ip default-network 100.1.1.0

R2 and R3 will see this route as adefault route discovered by RIP:

R2#show 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-ISlevel-2, ia - IS-IS inter area

* - candidate default, U - per-user


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static route, o - ODR

P - periodic downloaded static route

Gateway of last resort is 172.12.123.1 tonetwork 0.0.0.0



Loopback0


C 172.12.123.0 is directly connected,Serial0

R* 0.0.0.0/0 [120/1] via 172.12.123.1,

00:02:20, Serial0

The default route named by ip

default-network didn’t have to be

manually redistributed into RIP. It’s

placed there automatically by the


89/1409

router when this command is used.

Speaking of redistribution, we

could have created a default static

route on R1 and then redistributed i

into RIP. We’ll remove the ip

default-network command and do

ust that.

R1(config)#no ip default-network 100.0.0.0R1(config)#ip route 0.0.0.0 0.0.0.0 ethernet0

R1(config)#router rip

R1(config-router)#redistribute static metric 1

R2 and R3 will both see the defaul

route.


R* 0.0.0.0/0 [120/1] via 172.12.123.1,


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00:00:12, Serial0


R* 0.0.0.0/0 [120/1] via 172.12.123.1,00:00:02, Serial0

uch more redistribution to come!

IP Helper Addresses

While routers accept and generatebroadcasts, they do not forward

them. That can present quite a

problem with DHCP requests whea router is between the requestin

host and the DHCP server. The

initial step in the DHCP process hasthe host generating a


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HCPDiscover packet - and tha

packet is a broadcast.

If this PC attempts to locate a

DHCP server with a broadcast, the

broadcast will be stopped by the

router and will never get to theDHCP server. By configuring the ip


92/1409

helper-address command on the

router, UDP broadcasts such as this

will be translated into a unicast bythe router, making the

communication possible.

The command should be

configured on the interface that

will be receiving the broadcasts --

not the interface closest to thedestination device.

R1(config)#int e0R1(config-if)#ip helper-address ?

A.B.C.D IP destination address

R1(config-if)#ip helper-address 100.1.12


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DHCP messages are not the only

broadcasts being relayed to the

correct destination with thiscommand -- there are nine of them.

TIME, port 37

TACACS, port 49

DNS, port 53

BOOTP/DHCP Server, port 67

BOOTP/DHCP Client, port 68


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TFTP, port 69

NetBIOS name service, port

137

NetBIOS datagram service,

port 138

IEN-116 name service, port 42

That’s going to cover mosscenarios where the ip helper-


95/1409

address command will be useful,

but what about those situations

where the broadcast you needforwarded is not on this list? Yo

can use the ip forward-protocol

command to add any UDP por

number to the list.

To remove protocols from the list,

use the no ip forward-protocol command. In the followin

example, we’ll add the Networ

Time Protocol port to theforwarding list while removing the

etBIOS ports. Remember, you ca

use IOS Help to get a list ocommonly filtered ports!


96/1409

R1(config)#ipforward-protocol

udp ? Port number

biff

Biff (mail

notification, comsat,512)

bootpc

Bootstrap

Protocol (BOOTP)client (68)

bootps

Bootstrap

Protocol (BOOTP)server (67)

discard Discard (9)

DNSIX security


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dnsix protocol auditing(195)

domain Domain NameService (DNS, 53)

echo Echo (7)

isakmp(500)

Internet SecurityAssociation andKey ManagementProtocol

mobile-ipMobile IP

registration (434)

nameserver IEN116 name

service (obsolete,42)

netbios-dgm

NetBios datagramservice (138)


98/1409

netbios-ns NetBios name

service (137)

netbios-ss NetBios sessionservice (139)

ntpNetwork Time

Protocol (123) pim-auto-

rpPIM Auto-RP

(496)

rip

RoutingInformationProtocol (router,

in.routed, 520)

snmpSimple Network

ManagementProtocol (161)

SNMP Traps


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snmptrap (162)

sunrpc

Sun Remote

Procedure Call(111) syslog SystemLogger (514)

tacacs TAC AccessControl System (49)

talk Talk (517)

tftp

Trivial FileTransfer Protocol(69)

time Time (37)

whoWho service

(rwho, 513)X Display


100/1409

xdmcp Manager ControlProtocol (177)

R1(config)#ip forward-protocol udp 123

R1(config)#no ip forward-protocol udp 137

R1(config)#no ip forward-protocol udp 138

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101/1409

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Free CCNP ROUTE Video Boo

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103/1409

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104/1409

EIGRP Fundamentals

ntroduction To EIGRP

Link state protocols (OSPF) anddistance vector protocols (RIP)

have clear-cut differences in the

way the best routes are determinedand what is actually exchanged

between routers. Just as a hybrid

plant has characteristics of morethan one plant, a hybrid routin

protocol has characteristics of bot

link state and distance vector protocols. The hybrid protocol is


105/1409

nhanced Interior Gateway

outing Protocol – EIGRP.

EIGRP has a lot going for it:

Rapid convergence upon a

change in the network, because backup routes (“ Feasible

Successors”) are calculated

before they’re actually neededdue to the loss of a primary

route (“Successor ”)

Offers multiprotocol support

(supports IP, IPX, andAppleTalk)


106/1409

Supports Variable-Length

Subnet Masking (VLSM) andClassless Inter-Domain

Routing (CIDR)

The one little problem with EIGRP

is that it’s Cisco-proprietary,making it unsuitable for a

multivendor environment.

EIGRP is the enhanced version o

the original Interior Gateway

Routing Protocol (IGRP), which is

no longer supported by new Cisco

IOSes and is no longer a part o


107/1409

Cisco certification exams. I’ll

mention it occasionally in the

EIGRP sections for comparison’ssake.

EIGRP acts like a distance vector

protocol in that EIGRP neighbors

initially exchange full routin

tables. Just about every other

EIGRP behavior is more like a linstate protocol.

ello Packets and RTP: Theeartbeat Of EIGRP

EIGRP uses Hello packets(multicast to 224.0.0.10) to


108/1409

establish and maintain neighbor

relationships. The Reliable

Transport Protocol (RTP) is usedto handle the transport of messages

between EIGRP-enabled routers.

EIGRP also acts like a link state

protocol in that when networ

topology changes occur, updates

containing only the change are sent,

rather than another full routin

table.

EIGRP uses autonomous systems toidentify routers that will belong to

the same logical group. EIGRP

routers that exist in separateautonomous systems will no


109/1409

exchange routes. They won’t eve

become neighbors in the first place!

For an EIGRP neighbor relationship

to be established, the routers mus

receive Hello packets from the

neighbor, the Autonomous Syste

number must match, and the metric

weights must match.

The metric weights refer to the

level of importance EIGRP gives to

the bandwidth, delay, load , andreliability metrics. By default,

EIGRP considers bandwidth and

delay when calculating metrics, anddoes not consider the other metric


110/1409

weights.

Changing the metric weights is

covered in the Advanced EIGRP

section; for now, know that these

metric weights must be the same o

each router or the neighbor

relationship will not be established.

As with OSPF, once the neighbor relationship is present, it is the

Hello packets that keep it alive. I

the Hellos are no longer receivedby a router, the neighbor

relationship will eventually be

terminated.


111/1409

The Successor and Feasible

uccessor

EIGRP keeps three tables - the

route table, where the best route to

each destination is kept; the

topology table, where all feasible

routes are kept; and the neighbor

table, where the EIGRP neighbors

and information about them arekept.

As an EIGRP-enabled router learnsabout the network, the router will

put the best route to a give

destination in its routing table.EIGRP keeps the best routes alon


112/1409

with less-desirable but still valid

routes in the topology table. EIGRP

actually calculates these backuproutes before a failure occurs,

making convergence after a failure

much faster than RIP.

The EIGRP term for the best route

is Successor. Any valid alternate

route is referred to as the FeasibleSuccessor . The decision process

for whether a route can become a

Feasible Successor can be summedup in one question….

The EIGRP Feasible Successor Question:


113/1409

The router asks itself, “Is the

neighboring router’s metric for this

route lower than my metric?”

If so, no loop is present, and

that route is a FeasibleSuccessor.

If not, a loop may be present,

and that route cannot be aFeasible Successor.

That’s all well and good - but whaif there is no Feasible Successor?

EIGRP uses the Diffusing Updatelgorithm (DUAL) to issue queries


114/1409

to neighbors for a loop-free route to

the destination. If the routers

receiving the DUAL queries do nohave a route, those routers will also

send DUAL queries to their

neighbors. This process continues

until a route is found and the

original router is informed of the

route, or no valid route is found.

More about those queries later i

the two EIGRP sections.

IGRP’s Major Advantage Over

IP

EIGRP is Cisco-proprietary, and


115/1409

RIPv2 is not. Both support VLSM,

so why not use RIPv2 over EIGRP?

Consider the following:

If you or I were asked what theoptimal path(s) are between R1 and


116/1409

R2, we wouldn’t hesitate - T1 lines

run at 1544 kbps, almost thirty

times faster than a 56 kbps line, sothe extra “hop” over the R1 paths

will hardly matter.

EIGRP would agree with us, bu

RIPv2 would not. RIPv2 does have

its uses, but it only considers hop

count as a metric. Therefore, RIPv2would consider the path from R1-

R5-R2 the best path - and it’s

nowhere near the best path!

Since both EIGRP and OSPF

consider the speed of a link in itscalculations, we’re almost always


117/1409

better off to use those two protocols

for our WANs. OSPF is not Cisco-

proprietary, so if we do have somenon-Cisco routers (booooo!) in the

WAN, we could still use tha

instead of RIPv2.

Configuring EIGRP

EIGRP uses Autonomous Systemsto put EIGRP-enabled routers into

logical groups. For two routers to

become EIGRP neighbors, theymust agree on the AS number. To

enable EIGRP on a particular

interface, we’ll use the networ command. The use of wildcard


118/1409

masks is optional, but you’ll see

them in 99% of real-world EIGRP

deployments. Just watch that on theexam - EIGRP and OSPF both use

wildcard masks in their networ

statements, not subnet masks.


119/1409

R1#conf t

R1(config)#router eigrp 100

R1(config-router)#no auto-summary

R1(config-router)#network 172.12.123.0

0.0.0.255

R2#conf t

R2(config)#router eigrp 100 R2(config-

router)#no auto-summaryR2(config-router)#network 172.12.123.0

0.0.0.255

R3(config)#router eigrp 100R3(config-router)#network 172.12.0.0

0.0.255.255

R3(config-router)#no auto-summ


120/1409

ote that I disabled auto-

summarization on all three routers.

EIGRP has autosummarizatiorunning by default, and usually

you’re going to disable it eve

before you enter your networ

statements! You’ll see why - and

what can happen if you don’t

disable auto-summarization - later

in this chapter. You can also enter

the no auto-summary command

after your network statements, as

shown on R3.

Wildcard masks are used whe

configuring network numbers iEIGRP. This mask type allows the


121/1409

configuration to be more specific i

what interfaces will be runnin

EIGRP. With the above wildcardmasks, any interfaces in the networ

172.12.123.0 /24 will run EIGRP.

Wildcard Masks

Wildcard masks do look a little odd

at first, but since we use them iaccess lists, EIGRP, and OSPF, we

better know how to configure them!

They’re really just “reverse subne

masks”. For instance, the network

172.12.123.0 255.255.255.0 means


122/1409

that all hosts that begin with

172.12.123 are part of that network.

When you write out the networ

number and the mask in binary and

compare the two, the ones in the

subnet mask are “care” bits and the

zeroes are “don’t care” bits.

172.12.123.0 = 1010110000001100 01111011 00000000

255.255.255.0 = 1111111111111111 11111111 00000000

What do I mean by “care” and“don’t care”? For a host to be o


123/1409

the 172.12.123.0 /24 network, the

host’s address must match every bi

where there is a 1 in the networ mask. After that, I don’t care!

Wildcard masks take the opposite

approach. The zeroes are “I care”,

and the ones are “I don’t care”. I

this example, we want to enable

EIGRP on all interfaces whose firsthree octets are 172.12.123, and

after that, we don’t care!

10101100 00001100 01111011

00000000 = 172.12.123.0

00000000 00000000 00000000


124/1409

11111111 = 0.0.0.255

Using wildcard masks takes some

getting used to, and just make sure

to be careful on your exam:

Subnet masks begin wit

strings of consecutive 1s

Wildcard masks begin witstrings of consecutive 0s and

are required in OSPF networ

statements, but not EIGRPnetwork statements

ow let’s get back to our EIGRPdeployment!


125/1409

A few seconds after configuring the

three routers with EIGRP, this

console message appears on R1:

The Diffusing Update Algorith

(DUAL) has run and two new

neighbors, 172.12.123.2 and

172.12.123.3, have formed

adjacencies with R1. Show ip eigrp

neighbors gives the details:


126/1409

The key values are the IP addresses

of the EIGRP AS 100 neighbors, the

interface on which they werediscovered, and the Uptime,

indicating how long the neighbor

relationship has existed.

The loopbacks on each router will

now be added to EIGRP 100, as

well as the Ethernet segmenbetween R2 and R3. The etherne

segment’s network number is

172.23.23.0 /27, so we get a littlemore practice with our wildcard

masks! The loopbacks all have their

router number for each octet, andeach loopback has been configured


127/1409

with a host mask (255.255.255.255

or /32).

The additional configurations:


128/1409


R1(config-router)#network 1.1.1.1 0.0.0.0

R2(config)#router eigrp 100R2(config-router)#network 172.23.23.0 0.0.0.31


R3(config)#router eigrp 100R3(config-router)#network 172.23.23.0 0.0.0.31


show ip route eigrp 100 is then ru

at each router to ensure each router

is seeing the other routers’loopbacks, and that R1 is seeing the

Ethernet segment via EIGRP. R2

and R3 are both directly connectedto the 172.23.23.0 /27 network, so


129/1409

there will be no EIGRP route to tha

network in their EIGRP tables.

The Successor routes appear in two

of our three EIGRP tables. The

EIGRP Route table, seen with show

ip route eigrp, contains only the

Successor routes. R1 has two

Successor routes for 172.23.23.0

/27.

R1#show ip route eigrp


D 2.2.2.2 [90/2297856] via

172.12.123.2, 00:01:01, Serial0


D 3.3.3.3 [90/2297856] via

172.12.123.3, 00:00:58, Serial0



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D 172.23.23.0 [90/2195456] via

172.12.123.2, 00:01:01, Serial0

[90/2195456] via

172.12.123.3, 00:01:01, Serial0



D 1.1.1.1 [90/2297856] via172.12.123.1, 00:01:33, Serial0


D 3.3.3.3 [90/409600] via 172.23.23.3,

00:01:35, Ethernet0



D 1.1.1.1 [90/2297856] via

172.12.123.1, 00:01:46, Serial0


D 2.2.2.2 [90/409600] via 172.23.23.2,

00:01:49, Ethernet0


131/1409

As always, the first number in the

brackets is the protocol’s

Administrative Distance. Thesecond number is the EIGRP metric

for that route.

Each router sees the other routers’

loopbacks, and can ping them (pin

results not shown). R1 can not only

ping the Ethernet interfaces of R2and R3, but has two routes to tha

subnet in its routing table. EIGRP is

performing equal-cost loabalancing .

The metric for the route is 2195456for both routes, so data flows goin


132/1409

from R1 to the 172.23.23.0 /27

network will be balanced over the

two Frame Relay cloud links.

To see the Successor and Feasible

Successor routes in EIGRP, ru

show ip eigrp topology. On R1,

two successors for the route

172.23.23.0/27 exist, so both are

placed into the routing table as seepreviously. There are also two

routes for destinations 2.2.2.2/32

and 3.3.3.3/32, but those have nobeen placed into the EIGRP routin

table. Why?

R1#show ip eigrp topology

IP-EIGRP Topology Table for


133/1409

AS(100)/ID(1.1.1.1)

Codes: P - Passive, A - Active, U - Update, Q -

Query, R - Reply,

r - reply Status, s - sia StatusP 3.3.3.3/32, 1 successors, FD is 2297856

via 172.12.123.3 (2297856/128256),

Serial0

via 172.12.123.2 (2323456/409600),

Serial0

P 2.2.2.2/32, 1 successors, FD is 2297856

via 172.12.123.2 (2297856/128256),

Serial0

via 172.12.123.3 (2323456/409600),

Serial0


via Connected, Loopback0

P 172.23.23.0/27, 2 successors, FD is 2195456via 172.12.123.3 (2195456/281600),

Serial0

via 172.12.123.2 (2195456/281600),

Serial0P 172.12.123.0/24, 1 successors, FD is 2169856

via Connected, Serial0


134/1409

R1 has two valid, loop-free routes

to 2.2.2.2/32 and 3.3.3.3/32 in its

Topology table…


via 172.12.123.3 (2297856/128256),Serial0

via 172.12.123.2 (2323456/409600),

Serial0

P 2.2.2.2/32, 1 successors, FD is 2297856via 172.12.123.2 (2297856/128256),

Serial0

via 172.12.123.3 (2323456/409600),

Serial0

…. but the metrics are unequal, so

only the best path (the Successor) isplaced into the EIGRP Route table.


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D 2.2.2.2 [90/2297856] via

172.12.123.2, 00:12:54, Serial03.0.0.0/32 is subnetted, 1 subnets

D 3.3.3.3 [90/2297856] via

172.12.123.3, 00:12:51, Serial0

172.23.0.0/27 is subnetted, 1 subnetsD 172.23.23.0 [90/2195456] via

172.12.123.2, 00:12:54, Serial0

[90/2195456] via

172.12.123.3, 00:12:54, Serial0

The metrics for those routes are

very close, so close that it’s a good

idea for us to use both of them for load balancing. We can use the

variance command here to

configure unequal-cost loabalancing .


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The variance Command

The variance command is simply a

multiplier. The router will multiply

the Feasible Distance by this value.

Any feasible successor with a

metric less than that new value will

be entered into the routing table.

In print, that sounds a littleconfusing. In reality, it’s simple, as

you’re about to see!

Consider the path from R1 to R2’s

loopback in the previous tables.

The primary route has a metric o2297856; the other route has a


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metric of 2323456. By default, the

second route will serve only as a

backup and will not carry packetsunless the primary goes down.

By configuring variance 2 in R1’s

EIGRP process, the process

multiplies the metric of the bes

route (2297856) by the variance

value:

2297856 x 2 = 4595712

Any feasible successor with a

metric less than 4595712 will now

participate in unequal-cost loadsharing.


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R1’s feasible successor to 2.2.2.2

has a metric of 2323456, so i

qualifies! After changing thevariance value to 2 (by default, it’s

1) and clearing the routing table,

show ip route eigrp 100 verifies

that two valid routes to both R2’s

and R3’s loopbacks appear in the

EIGRP routing table.


R1(config-router)#variance ?

Metric variance multiplier

R1(config-router)#variance 2

R1#clear ip route * (clears the routing table o

all dynamically learned routes)


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D 2.2.2.2 [90/2297856] via

172.12.123.2, 00:00:26, Serial0[90/2323456] via

172.12.123.3, 00:00:26, Serial0 3.0.0.0/32 is

subnetted, 1 subnets

3.3.3.3 [90/2297856] via 172.12.123.3,00:00:26, Serial0

[90/2323456] via

172.12.123.2, 00:00:26, Serial0

172.23.0.0/27 is subnetted, 1 subnetsD 172.23.23.0 [90/2195456] via

172.12.123.2, 00:00:26, Serial0

[90/2195456] via

172.12.123.3, 00:00:26, Serial0

The variance command does no

actually change the metrics; imakes a higher metric acceptable


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for load sharing.

utosummarization - One Default

You’ll Want To Change

EIGRP and RIP version 2 perfor autosummarization by default,

which is the act of summarizin

network routes when those routesare sent across a network boundary;

that is, when they are advertised via

an interface that is not part of thenetwork being summarized.

In the earlier lab, I disabledautosummarization immediately, bu


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I will not do so here.

To illustrate, we’ll use a hub-and-

spoke network where both spokes

have subnets of 20.0.0.0/8. The

Serial interfaces are all on the

172.12.123.0 /24 network, with the

router number serving as the final

octet. All interfaces will be placed

into EIGRP AS 100.


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Here are the current configurations.I did not configure the auto-

summary command -- it’s on by

default and will appear in the router configuration.

R1:

router eigrp 100

network 172.12.123.0 0.0.0.255

auto-summary

R2:

router eigrp 100network 20.1.0.0 0.0.255.255


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network 20.2.0.0 0.0.255.255

network 172.12.0.0

auto-summary

R3:

router eigrp 100

network 20.3.0.0 0.0.255.255network 20.4.0.0 0.0.255.255

network 172.12.0.0

auto-summary

etwork 20.0.0.0 is discontiguous

there is no single path to allsubnets of the major networ

number. That’s a problem for

routing protocols such as RIPv1 thado not carry subnet mas


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information.

EIGRP and RIPv2 do carry subne

mask information, but the defaul

autosummarization causes trouble

with this network. R1 is now

receiving the exact same update

from both R2 and R3, and it’s for

the classful network 20.0.0.0 /8.


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Here’s R1’s EIGRP route table.

one of the subnets are present i

the routing table.

R1#show ip route eigrpD 20.0.0.0/8 [90/2297856] via

172.12.123.3, 00:11:19, Serial0[90/2297856] via

172.12.123.2, 00:11:19, Serial0

Since the metrics for both paths are

exactly the same, equal-cost loa

balancing for the classful networ 20.0.0.0 will be performed,

ensuring that at least half of the

packets destined for any particular subnet of 20.0.0.0 will be going to


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the wrong router.

If the metric were unequal, a single

route for the classful networ

20.0.0.0 would be placed into the

routing table. All packets for the

four subnets will go to the same

router, and two of the four subnets

will never receive any packets tha

were originally intended for them.

I’ll ping each loopback IP address

from R1 - as you’d guess from tharouting table, we’re going to ge

some really interesting results.

R1#ping 20.1.1.1


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timeout is 2 seconds:!U!.!



R1#ping 20.2.2.2



timeout is 2 seconds:U!.!U



R1#ping 20.3.3.3



timeout is 2 seconds:

U!.!U



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R1#ping 20.4.4.4

Type escape sequence to abort.Sending 5, 100-byte ICMP Echos to 20.4.4.4,

timeout is 2 seconds:

!U!.!

Success rate is 60 percent (3/5), round-tripmin/avg/max = 68/68/68 ms

That is one ugly combination o

successful pings, timeouts, andUnreachables - and an ugly success

rate as well.

This default behavior is easily

removed with the no auto-summary

command. When both of the routerssending updates add this command


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to their EIGRP configuration, the

routes will no longer be

summarized at the networ boundary.

One often-ignored side effect o

adding no auto-summary to a

existing EIGRP configuration - the

adjacencies will drop.


R3(config-router)#no auto-summary

R3(config-router)#^Z

R3#wr 00:26:09: %DUAL-5-NBRCHANGE: IP-

EIGRP 100: Neighbor 172.12.123.1 (Serial0) is

down: summary configured


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After configuring no auto-summary

on both R2 and R3 and waiting for

the adjacencies to reform, R1 nowhas a much more accurate routin

table.

R1#show ip route eigrp20.0.0.0/16 is subnetted, 4 subnets

D 20.4.0.0 [90/2297856] via

172.12.123.3, 00:00:11, Serial0

D 20.1.0.0 [90/2297856] via172.12.123.2, 00:03:47, Serial0

D 20.2.0.0 [90/2297856] via

172.12.123.2, 00:03:47, Serial0

D 20.3.0.0 [90/2297856] via172.12.123.3, 00:00:20, Serial0


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Bottom line: If you’re runnin

EIGRP and you’re not seeing the

subnets or routes you expect, the

first thing I’d check is to see if theno auto-summary command is i

the configuration. If it’s not, I’d pu

it there.


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router eigrp 100

network 20.3.0.0 0.0.255.255

network 20.4.0.0 0.0.255.255

network 172.12.0.0auto-summary


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one and a maximum of 16.


R1(config-router)#maximum-paths ? Number of paths

Setting maximum-paths to 1

disables load balancing.

UAL Queries And Why“Passive” Is A Good Thing

EIGRP uses the Diffusing UpdateAlgorithm (DUAL) to calculate

routes, and there’s one other

important role DUAL plays in aEIGRP deployment.


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If a Successor route is lost and

there is no Feasible Successor,

we’ve got a problem! DUALdoesn’t give up easily, though.

DUAL will mark the route as

ctive, indicating that the route is

being calculated and cannot be used

to route data, and will send out a

Query message to all of tha

router’s EIGRP neighbors.

A DUAL Query is basically oneneighbor asking another, “Hey, do

you know how to get to this networ

I just lost my route to?” If thaneighbor has a route, the query will


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be answered with that route. If the

neighbor doesn’t have such a route,

that neighbor will ask its neighbors.The process continues until a

downstream router replies with the

desired route, or the EIGRP

downstream routers run out o

neighbors to ask.

Routes in the EIGRP Topology table

marked as Active are considered

unusable, since Active indicatesthat the route is currently bein

calculated by DUAL. Hopefully the

route comes out of Active veryquickly and becomes Passive, as


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indicated by the “P” in the

following Topology table. When i

comes to EIGRP routes, Passive isgood and Active is bad!

R1#show ip eigrp topology

IP-EIGRP Topology Table for AS(100)/ID(1.1.1.1)

Codes: P - Passive, A - Active, U - Update,

Q - Query, R - Reply,

r - reply Status, s - sia StatusP 3.3.3.3/32, 1 successors, FD is 2297856

via 172.12.123.3 (2297856/128256),

Serial0

via 172.12.123.2 (2323456/409600),Serial0


via 172.12.123.2 (2297856/128256),

Serial0 via 172.12.123.3 (2323456/409600),

Serial0


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Back To Index

Recommended Video Viewing:

EIGRP Tables and Commands:

http://www.youtube.com/watch?v=ZndBgShoxl4

Advanced EIGRP Concepts:

http://www.youtube.com/watch?

v=LPuXmiKznEI

Video Practice Exam on RouteRedistribution:

http://www.youtube.com/watch?v=LPuXmiKznEIhttp://www.youtube.com/watch?v=ZndBgShoxl4


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http://www.youtube.com/watch?

v=eY2yyRd0lvM

The Mystery Of The AD 5:

http://www.youtube.com/watch?v=X9AzQCt7rCM

Free CCNP ROUTE Video Boo

Camp on route redistribution:

http://bit.ly/Arnhjq

Enjoy! -- Chris B.

http://bit.ly/Arnhjqhttp://www.youtube.com/watch?v=X9AzQCt7rCMhttp://www.youtube.com/watch?v=eY2yyRd0lvM


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Intermediate And Advanced

EIGRP Concepts And

Configuration

IGRP Fundamentals

Let’s take a few minutes to reviewEIGRP fundamentals and add to

those mentioned in the Basic EIGRP

section.

EIGRP is a Cisco-proprietary

protocol that improves greatly othe original version of this protocol,


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the Interior Gateway Routing

rotocol (IGRP). (The “E” i

EIGRP stands for enhanced .)

The benefits of using EIGRP

include:

Support for Appletalk, IP, and

IPX (Novell Netware) via

protocol-dependent modules(PDMs)

Support for variable-length

subnet masking (VLSM)

Dynamic neighbor discovery


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via packets multicast to

224.0.0.10

Fast convergence after

network topology changes -

backup routes are actuallycalculated and placed into a

table in advance of their

actually being needed. (Note:This table is NOT the IP

routing table.)

Where RIP sends routing

updates every 30 seconds,even if nothing has changed,


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EIGRP will send routing

updates only when a network

topology change actuallyoccurs.

EIGRP updates do not containthe entire routing table, but

reflect only the routes that

have been changed.

The scope of these updates islimited to the routers that

actually need them - they’re

not flooded.


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Those last two points might no

sound like much, but everything we

do on a Cisco router has a cost iCPU and time. If your routing table

has 105 routes and only 1 has

changed, why take the time to create

an update for every single route

when an update reflecting only the

change will serve our purpose?

EIGRP’s routing algorithm is the

Diffusing Update Algorith

(DUAL). DUAL not only calculatesroutes that ensure a loop-free

network, but also calculates backup

routes before they’re needed.


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These backup routes, the feasible

successors, are kept in the EIGRP

topology table. The primary routes,the successors, are kept in both the

EIGRP topology and route tables.

EIGRP’s third table is the neighbor

table, which contains just what yo

would think it does - informatio

about EIGRP neighbors.

EIGRP is a classless routin

protocol, which means it supports

Variable Length Subnet Maskin(VLSM). EIGRP routing update

packets contain a prefix length for

each individual network, makinVLSM support possible.


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EIGRP uses metric weights to

determine how important certai

values are in route calculation. Bydefault, bandwidth and delay are

the only metric values used in route

calculation. The other metric

weights, or “k-weights”, are load,

reliability, and MTU .

You can change the bandwidth anddelay values to alter EIGRP pat

selection. If you’re changing any

EIGRP values to fine-tune your routing table, I’d go with bandwidt

as it’s simply easier to get the

desired results.


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The bandwidth command is entered

in kbps and should be set to the

minimum bandwidth of the path.The delay command is configured

in tens of microseconds. As you’d

guess, the bandwidth command is

easier to use for fine-tuning routes.

R1(config)#int s0

R1(config-if)#bandwidth ? Bandwidth in kilobits

R1(config-if)#bandwidth 64

R1(config-if)#delay ? Throughput delay (tens of

microseconds)

Since DUAL actually calculates


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backup routes before they’re eve

needed, EIGRP responds to

topology changes faster than RIP(which isn’t saying much) and

OSPF (which is saying a lot). Wit

EIGRP, routing loops have literally

no time to form.

EIGRP will perform equal-cos

load-sharing over four paths bydefault, with a maximum of 16

paths. That value is configurable

with the maximum-paths command.


R1(config-router)#maximum-paths ?

Number of paths


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We can also perform unequal-cos

load balancing with EIGRP, and

we’ll practice that skill later in thissection.

Almost all EIGRP packets are

multicast to 224.0.0.10, and use IP

protocol number 88. Let’s take a

look at the different EIGRP packe

types… and see if we can spot thaexception to the multicast rule.

IGRP Packet Types And RTP

EIGRP uses the Reliable Transport

rotocol (RTP) to handle theguaranteed and reliable delivery o


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EIGRP packets to neighbors.

“Guaranteed and reliable” sounds a

lot like TCP, but the two are quitedifferent in how they operate. No

all EIGRP packets are going to be

sent reliably.

Hello packets are used for

neighbor discovery and to

keep existing neighbor relationships alive; these are

multicast to 224.0.0.10.

Acknowledgement packets

themselves are simply hello packets that contain no data.


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Neither Acks nor Hellos use

RTP, and are therefore

considered unreliable.

Update packets are sent to

new neighbors to allow theneighbor to build an accurate

routing and topology table, and

are also sent when a change inthe network occurs. Update

packets are generally multicast

packets, but there’s oneimportant exception that you’ll

read about later in this section.


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Query packets are sent when a

router loses a successor route

and has no feasible successor.

Reply packets are sent in

response to query packets, anda reply packet indicates that a

new route to the destination

has been found. Update, query,and reply packets all use RTP

and are considered reliable.

To see how many of these packets

have passed through a router, ru

show ip eigrp traffic.


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R1#show ip eigrp traffic

IP-EIGRP Traffic Statistics for process 100

Hellos sent/received: 2/2

Updates sent/received: 13/4Queries sent/received: 0/0

Replies sent/received: 0/0

Acks sent/received: 0/2

Input queue high water mark 1, 0 drops

SIA-Queries sent/received: 0/0

SIA-Replies sent/received: 0/0

To review: Hello and ACK packetsare unreliable. Reply, Query, and

Update packets are reliable.

That’s a handy troubleshootin

command, too. If the Query, Reply,

and Update values remain the same

over a period of time, your networ

is stable.


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If they’re constantly incrementing,

there’s a problem. The Query and

Reply values will increment only ia successor route is lost. If you see

those incrementing regularly, yo

have yourself a flapping lin

(believe me, I’ve been there). If the

SIA values are incrementing alon

with them, that’s not good - more o

that later in this part of the course.

ow EIGRP Routers Become

eighbors

EIGRP routers form neighbor


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relationships, and after the initial

exchange of routing updates

between neighbors, EIGRP routerswill then only send routing updates

when there is a change in the

network topology. These neighbor

relationships, or adjacencies, begi

when a router first has EIGRP

enabled on some or all of its

interfaces with the router eigrp

command.

In the following example, R1 isrunning EIGRP on a Serial

interface. R1 will multicast a

EIGRP Hello packet to 224.0.0.10out that interface in an attempt to


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find potential neighbors.

A downstream router, R2, receives

this Hello. If certain values areagreed upon between the two, R2

will respond with an EIGRP Update

packet, which contains all theEIGRP-derived routes that R2

knows.


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Did you notice that the EIGRP

Update packet going back to R1

was a unicast? Generally, EIGRP

Update packets are multicast to

224.0.0.10, just as EIGRP Hello

packets are.

There’s almost always an exceptio

in networking, and that’s true here

as well. Update packets are unicasin this particular situation, bu


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otherwise they’re multicast.

R1 will send an EIGRP

Acknowledgement packet, or ack ,

to let R2 know the routes in the

Update packet were received. R1

will also send an Update packet o

its own, unicast to R2, containin

all EIGRP routes R1 has. R2 will

respond with an ack of its own.


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Other EIGRP Adjacency Issues

(And Non-Issues)

Unlike OSPF, EIGRP does not

require neighbors to agree on hello

and dead times. The EIGRP hold

time has the same function as OSPF

dead time - they’re both the

duration of time in which a hello

must be received in order to retaithe neighbor relationship. The

default EIGRP hold time is three

times the hello time.

In the following example, a

adjacency has been formed betweeR2 and R3 using the default values

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