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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
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Bulldog”
Chris Bryant
CCIE #12933
“The Computer Certification
Bulldog”
Website:
http://www.thebryantadvantage.co
Twitter:
http://www.twitter.com/ccie12933
Facebook: http://on.fb.me/gPq52d
Blog:
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YouTube:
http://www.youtube.com/user/ccie1
http://www.youtube.com/user/ccie12933
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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:
http://www.youtube.com/user/ccie1
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.
http://www.youtube.com/user/ccie12933
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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:
http://www.thebryantadvantage.co
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
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http://www.thebryantadvantage.co
TSHOOT:
http://www.thebryantadvantage.co
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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http://www.thebryantadvantage.co
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:
http://www.twitter.com/ccie12933
Facebook: http://on.fb.me/gPq52d
Bulldog Blog:
http://thebryantadvantage.blogspot.c
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:
http://www.thebryantadvantage.co
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
http://www.thebryantadvantage.com/CCNPROUTEStudyGuideUpgrade.htm
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Bulldog”
http://www.thebryantadvantage.co
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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
names are the trademarks,
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
liability or responsibility to any
person or entity with respect to lossor damages incurred from the
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
Copyright © 2012 The Bryant Advantage.
All Rights Reserved.
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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.
2. If there are multiple routes
to a destination and they havethe same prefix length, the
route with the lowest
administrative distance isused.
3. If there are multiple routes
with the same prefix length and
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AD, the route with the lowest
metric is used.
4. If there are multiple routes
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
172.12.0.0/16 is variably subnetted, 2
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
172.12.0.0/16 is variably subnetted, 2
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
10.0.0.0/24 is subnetted, 1 subnets
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
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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
< code table removed for clarity >
Gateway of last resort is 0.0.0.0 to network
0.0.0.0
172.12.0.0/16 is variably subnetted, 2
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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
10.0.0.0/24 is subnetted, 1 subnets
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
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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
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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
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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:
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R1#show ip route rip
172.12.0.0/16 is variably subnetted, 2
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 ?
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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
< code table removed for clarity >
172.12.0.0/16 is variably subnetted, 3
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
C 172.12.123.0/24 is directlyconnected, Serial0
10.0.0.0/24 is subnetted, 1 subnets
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C 10.1.1.0 is directly connected,
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
< code table removed for clarity >
172.12.0.0/27 is subnetted, 1 subnets
S 172.12.23.0 [200/0] via 210.1.1.3
10.0.0.0/24 is subnetted, 1 subnets
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 >
172.12.0.0/16 is variably subnetted, 2
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
C 172.12.123.0/24 is directlyconnected, Serial0
10.0.0.0/24 is subnetted, 1 subnets
C 10.1.1.0 is directly connected,
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
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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.
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The ip default-network command is
used to flag a network as a
candidate default route. The routersare already running RIP over the
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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
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected,
Loopback0
172.12.0.0/24 is subnetted, 1 subnets
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
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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.
R2#show ip route rip
R* 0.0.0.0/0 [120/1] via 172.12.123.1,
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00:00:12, Serial0
R3#show ip route rip
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
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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-
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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!
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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)
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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
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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
Recommended Video Viewing:
Three-part Video Boot Camp o
Floating Static Routes on TBA
website:
http://bit.ly/bxNIBh
Three-part Video Boot Camp series
http://bit.ly/bxNIBh
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on Static Routes on TBA Website:
http://bit.ly/dourQ2
Free CCNP ROUTE Video Boo
Camp on route redistribution:
http://bit.ly/Arnhjq
My CCNP ROUTE Video Boo
Camp - Exclusive Discount Lin
For My Ebook Readers Only!
http://bit.ly/Arnhjqhttp://bit.ly/dourQ2
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Just click this link for a free hour-
long preview AND $10 off the
already low price!
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Available for immediate download
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and on DVD!
Copyright © 2012 The Bryant Advantage.
All Rights Reserved.
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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
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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)
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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
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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
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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
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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
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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.
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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
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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:
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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
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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
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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
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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
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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
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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.
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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
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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
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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
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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
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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
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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!
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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:
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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
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with a host mask (255.255.255.255
or /32).
The additional configurations:
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R1(config)#router eigrp 100
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
R2(config-router)#network 2.2.2.2 0.0.0.0
R3(config)#router eigrp 100R3(config-router)#network 172.23.23.0 0.0.0.31
R3(config-router)#network 3.3.3.3 0.0.0.0
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
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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
2.0.0.0/32 is subnetted, 1 subnets
D 2.2.2.2 [90/2297856] via
172.12.123.2, 00:01:01, Serial0
3.0.0.0/32 is subnetted, 1 subnets
D 3.3.3.3 [90/2297856] via
172.12.123.3, 00:00:58, Serial0
172.23.0.0/27 is subnetted, 1 subnets
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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
R2#show ip route eigrp
1.0.0.0/32 is subnetted, 1 subnets
D 1.1.1.1 [90/2297856] via172.12.123.1, 00:01:33, Serial0
3.0.0.0/32 is subnetted, 1 subnets
D 3.3.3.3 [90/409600] via 172.23.23.3,
00:01:35, Ethernet0
R3#show ip route eigrp
1.0.0.0/32 is subnetted, 1 subnets
D 1.1.1.1 [90/2297856] via
172.12.123.1, 00:01:46, Serial0
2.0.0.0/32 is subnetted, 1 subnets
D 2.2.2.2 [90/409600] via 172.23.23.2,
00:01:49, Ethernet0
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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
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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
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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
P 1.1.1.1/32, 1 successors, FD is 128256
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
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R1 has two valid, loop-free routes
to 2.2.2.2/32 and 3.3.3.3/32 in its
Topology table…
P 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 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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R1#show ip route eigrp
2.0.0.0/32 is subnetted, 1 subnets
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 eigrp 100
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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R1#show ip route eigrp
2.0.0.0/32 is subnetted, 1 subnets
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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Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 20.1.1.1,
timeout is 2 seconds:!U!.!
Success rate is 60 percent (3/5), round-trip
min/avg/max = 68/68/68 ms
R1#ping 20.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 20.2.2.2,
timeout is 2 seconds:U!.!U
Success rate is 40 percent (2/5), round-trip
min/avg/max = 68/68/68 ms
R1#ping 20.3.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 20.3.3.3,
timeout is 2 seconds:
U!.!U
Success rate is 40 percent (2/5), round-trip
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min/avg/max = 68/68/68 ms
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 eigrp 100
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 eigrp 100
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
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
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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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Copyright © 2012 The Bryant Advantage.
All Rights Reserved.
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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 eigrp 100
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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