distance vactor routing protocol igrp

8/14/2019 Distance Vactor Routing Protocol Igrp

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Ch. 7 – Distance Vector Routing ProtocolsPart 2 of 2: Distance Vector Routing and

IGRP

CCNA version 1.0Rick Graziani

Cabrillo College



Rick Graziani [email protected] 2

Note to instructors

• If you have downloaded this presentation from the Cisco NetworkingAcademy Community FTP Center, this may not be my latest version of this PowerPoint.

• For the latest PowerPoints for all my CCNA, CCNP, and Wirelessclasses, please go to my web site:

http://www.cabrillo.cc.ca.us/~rgraziani/• The username is cisco and the password is perlman for all of

my materials.• If you have any questions on any of my materials or the curriculum,

please feel free to email me at [email protected] (I really don’tmind helping.) Also, if you run across any typos or errors in mypresentations, please let me know.

• I will add “(Updated – date )” next to each presentation on my web sitethat has been updated since these have been uploaded to the FTPcenter.

Thanks! Rick




IGRP Features

• IGRP is a distance vector routing protocol developed by Cisco.• IGRP sends routing updates at 90 second intervals, advertising

networks for a particular autonomous system.

• Key design characteristics of IGRP are a follows: – The versatility to automatically handle indefinite, complex

topologies – The flexibility needed to segment with different bandwidth and

delay characteristics

– Scalability for functioning in very large networks




IGRP Features

• By default, the IGRP routing protocol uses bandwidth and delay asmetrics.

• Additionally, IGRP can be configured to use a combination of variables

to determine a composite metric.• Those variables include:

– Bandwidth – Delay – Load – Reliability




IGRP Metrics




IGRP Metrics

• The metrics that IGRP uses are: – Bandwidth – The lowest bandwidth value in the path – Delay – The cumulative interface delay along the path – Reliability – The reliability on the link towards the destination as

determined by the exchange of keepalives

– Load – The load on a link towards the destination based on bits per second – NO… MTU – The Maximum Transmission Unit value of the path.

MTU has never been used by IGRP or EIGRP as a routingmetric.

• IGRP has an administrative distance of 100 , more “trustworthy” thanRIP at 120.

• This means a Cisco router will prefer an IGRP learned route over aRIP learned route to the same network.


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Administrative Distances

Cisco Default Administrative Distances

Route Source Administrative DistanceConnected interface

Static Route

EIGRP summary route

External BGP

EIGRP

IGRP

OSPF

IS-IS

RIPEGP

External EIGRP

Internal BGP

Unknown

0

1

5

20

90

100

110

115

120140

170

200

255



IGRP Metrics



IGRP Routes

• Interior “Interior routes are routes between subnets of a network attached to arouter interface. If the network attached to a router is not subnetted,IGRP does not advertise interior routes.”

• Clarification• IGRP also advertises three types of routes:

– interior, system, and exterior.• Interior routes are routes between subnets in the network attached to a

router interface.• If the network attached to a router is not subnetted, IGRP does not

advertise interior routes.



IGRP Routes

• System“System routes are routes to networks within an autonomous system.The Cisco IOS software derives system routes from directly connectednetwork interfaces and system route information provided by other IGRP-speaking routers or access servers. System routes do not includesubnet information.”



IGRP Routes

• Exterior “Exterior routes are routes to networks outside the autonomous systemthat are considered when identifying a gateway of last resort. The CiscoIOS software chooses a gateway of last resort from the list of exterior routes that IGRP provides. The software uses the gateway (router) of last resort if a better route is not found and the destination is not aconnected network. If the autonomous system has more than oneconnection to an external network, different routers can choosedifferent exterior routers as the gateway of last resort.”



IGRP Timers

• IGRP has a number of features that are designed to enhance itsstability, such as: – Holddowns – Split horizons – Poison reverse updates



IGRPTimers

• The update timer specifies how frequently routing update messagesshould be sent.

• The IGRP default for this variable is 90 seconds .• A random jitter variable of 20% is subtracted from each update time to

prevent update timer synchronization.• IGRP updates will vary from 72 to 90 seconds.

Update timer



IGRPTimers

• The invalid timer specifies how long a router should wait in the absenceof routing-update messages about a specific route before declaring thatroute invalid (unreachable), but still in the routing table .

• The IGRP default for this variable is three times the update period or 270 seconds .

• Then placed in the holddown state.• “If I haven’t heard from you in 270 seconds, I am considering this route

as unreachable, I will start the holddown timer, but I will keep it in theroutin table until the flush timer ex ires.”

Invalid timer



IGRPTimers

• The holddown timer specifies the amount of time for whichinformation about poorer routes are ignored.

• Zinin: “Holddown specifies the number of seconds that a route mustspend in holddown state after expiration of the Invalid Timer.”

• The IGRP default for this variable is three times the update timer period plus 10 seconds = 280 seconds .

• The original route is still in the routing table but marked asunreachable, until the flush timer expires.

Holddowntimer



IGRPTimers

• Finally, the flush timer indicates how much time should pass before a route isflushed from the routing table.

• The IGRP default is seven times the routing update timer or 630 seconds .• Zinin: “Flush specifies the number of seconds that a route must remain in the

routing table in the garbage collection state after it exits the holddown state.”

• Each time an update is received the invalid and flush timers are reset .• If the invalid timer expires before another update is heard, the route is marked

as unreachable , but remains in the routing table.• If the flush timer then expires before another update is heard, the route will be

deleted from the routing table .

Flush timer



IGRP Timers

• Update timer : how frequently routing update messages should be sent• Invalid timer : how long a router should wait in the absence of routing-update messages

about a specific route before declaring that route invalid (unreachable), but still in therouting table

• Holddown timer : specifies the amount of time for which information about poorer routesare ignored.

• Flush timer : how much time should pass before a route is flushed from the routing table

90 secs – Update and Invalid timers are then reset.Update

270 secs - Invalid timer expires, route now“unreachable” but still in routing table until flush timer expires. Holddown timer of 280 sec begins.

Invalid

280 secs – Holddown timer

expires, will now accept a poorer route tosame network. Still in routing table

Holddown

630 secs –Route will now beremoved from therouting table.

FlushMy testing shows that the flush timer startsafter the first 90 second update is missed.



IGRPTimers

• All timers begin at the same time. – Update timer = 90 seconds – Invalid timer = 270 seconds – Holddown timer = 280 seconds – Flush timer = 630 seconds

• Today, IGRP is showing its age, it lacks support for variable lengthsubnet masks (VLSM).

• Enhanced IGRP (EIGRP) supports VLSM.



Configuring IGRP

• Same network commands as RIP.• IGRP “AS” number must be the same on all routers.



Configuring IGRP

timers basic (IGRP)• To adjust Interior Gateway Routing Protocol (IGRP)

network timers, use the timers basic router configurationcommand. To restore the default timers, use the no form of this command.

Router(config-router)# router igrp 100Router(config-router)# timers basic update invalid holddown

flush [ sleeptime ]Router(config-router)# no timers basic



Verifying IGRP




Troubleshooting IGRP




Rick’s extra information on autonomous systems …(FYIonly!)

Two types of autonomous systems:1. Process domain2. Routing domain

Domains…




Process domain• A single IGP (Interior Gateway Protocol) process that is

autonomous from other IGP processes.

IGRP autonomous systems are also known as a processdomains.

Redistribution is used to route between these types of

autonomous systems.

Domains…




Routing domain• A system of one or more IGPs (Interior Gateway

Protocols) that is autonomous from other IGP

systems.

• An EGP (Exterior Gateway Protocol) like BGP is usedto route between these types of autonomous systems.

Domains…




R o u t e r R o u t e r

R o u t e r

R o u t e r


R o u t e r


R o u t e r

R o u t e r

B G P

A S 9 0

A S 1 0

I G R P 4 0I G R P 3 0

P r o c e s s D o m a i n

P r o c e s s D o m a i n

R o u t i n g D o m a i n

R o u t i n g D o m a i n

T w o T y p e s o f A u t o n o m o u s S y s t e m s :P r o c e s s D o m a i n s a n d R o u t in g D o m a i n s




Summary

But there is still more!



IGRP Metric Information (and for EIGRP as well!)




The metrics used by IGRP in making routing decisions are (lower the metric the

better):• bandwidth• delay• load• reliability

By default, IGRP uses only:• Bandwidth• Delay

Analogies :

Think of bandwidth as the width of the pipeand

delay as the length of the pipe .

• Bandwidth is a the carrying capacity

• Delay is the end-to-end travel time .

Metric Calculation




If these are the default:

• bandwidth (default)• delay (default)

When are these used?• load• reliability

Only when configured by the network administrator to do so!IGRP also tracks (but does not use in its metric calculation):• MTU (Maximum Transmission Unit)• Hop Count

Use show interface command to view the metrics used on a specific interfacethat is routing EIGRP.

• These are the raw values .

Metric Calculation




Router> show interfaces s1/0Serial1/0 is up, line protocol is up

Hardware is QUICC SerialDescription: Out to VERIOInternet address is 207.21.113.186/30

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,rely 255/255, load 246/255

Encapsulation PPP, loopback not setKeepalive set (10 sec)

<output omitted>

bandwidth delay

reliability load

Metric Calculation



Rick Graziani [email protected]

Metric Calculation (Review)

EIGRP

– k1 for bandwidth – k2 for load – k3 for delay – k4 and k5 for Reliability

Router(config-router)# metricweights tos k1 k2 k3 k4 k5

bandwidth is in kbps

Bandwidth BW IGRP DLY IGRP




Media

BandwidthK= kilobits

BW IGRP

10,000,000/Bandwidth DelayDLY IGRP

Delay/10

100M ATM 100,000K 100 100 µ S 10Fast Ethernet 100,000K 100 100 µ S 10FDDI 100,000 100 100 µ S 10HSSI 45,045K 222 20,000 µ S 2,00016M Token Ring 16,000K 625 630 µ S 63

Ethernet 10,000K 1,000 1,000 µ S 100T1 (Serial Default) 1,544K 6,476 20,000 µ S 2,000512K 512K 19,531 20,000 µ S 2,000DS0 64K 156,250 20,000 µ S 2,00056K 56K 178,571 20,000 µ S 2,000

BW IGRP and DLY IGRP display values as sent in IGRP updates and used in calculatingthe IGRP metric.

MediaBandwidthK= kilobits

BW EIGRP

10,000,000/Bandwidth

*256 Delay

DLY EIGRPDelay/10

*256

100M ATM 100,000K 25,600 100 µ S 2,560Fast Ethernet 100,000K 25,600 100 µ S 2,560FDDI 100,000K 25,600 100 µ S 2,560HSSI 45,045K 56,832 20,000 µ S 512,00016M Token Ring 16,000K 160,000 630 µ S 16,128Ethernet 10,000K 256,000 1,000 µ S 25,600T1 (SerialDefault)

1,544K 1,657,856 20,000 µ S 512,000

512K 512K 4,999,936 20,000 µ S 512,000DS0 64K 40,000,000 20,000 µ S 512,00056K 56K 45,714,176 20,000 µ S 512,000

BW EIGRP and DLY EIGRP display values as sent in EIGRP updates and used incalculating the EIGRP metric.

Viva la

difference!

IGRP

EIGRP

Calculated values(cumulative) displayedin routing table (showip route).

EIGRP values are 256times greater.




Displaying Interface Values

shows reliability as a fraction of 255, for example (higher is better):

rely 190/255 (or 74% reliability)rely 234/255 (or 92% reliability)rely 255/255 (or 100% reliability)

Router> show interface s0/0Serial0/0 is up, line protocol is up

Hardware is QUICC SerialDescription: Out to VERIOInternet address is 207.21.113.186/30MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

rely 255/255, load 246/255Encapsulation PPP, loopback not setKeepalive set (10 sec)

<output omitted>

Bandwidth Delay

Reliability Load

shows load as a fraction of 255, for example (lower is better):

load 10/255 (or 3% loaded link)load 40/255 (or 16% loaded link)load 255/255 (or 100% loaded link)




Displaying Interface Values

Router> show interface s0/0Serial0/0 is up, line protocol is up

Hardware is QUICC SerialDescription: Out to VERIOInternet address is 207.21.113.186/30MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,


<output omitted>

Bandwidth Delay

Reliability Load

Routing Table Metric• Default: Slowest of bandwidth plus the sum of the delays of

all outgoing interfaces from “this router” to the destinationnetwork.




Bandwidth

• Expressed in kilobits (show interface )• This is a static number and used for metric calculations only.• Does not necessarily reflect the actual bandwidth of the link.• It is an information parameter only .• You cannot adjust the actual bandwidth on an interface with this command.

• Use the show interface command to display the raw value

The default values:• Default bandwidth of a Cisco interface depends on the type of interface.

• Default bandwidth of a Cisco serial interface is 1544 kilobits or 1,544,000bps (T1), whether that interface is attached to a T1 line (1.544 Mbps) or a 56Kline.

• IGRP metric uses the slowest bandwidth of all of the outbound interfaces to

the destination network.

Metric Calculation




Changing the bandwidth informational parameter:

The bandwidth can be changed using: Router(config-if)# bandwidth kilobits

To restore the default value:Router(config-if)# no bandwidth

Metric Calculation




Delay

• Like bandwidth, delay it is a static number .• Expressed in microseconds , millionths of a second • (Uses the Greek letter mu with an S, µ S, NOT “ms” which is millisecond or

thousandths of a second )• Use the show interface command to display the raw value

• It is an information parameter only .

The default values:• The default delay value of a Cisco interface depends upon the type of

interface .

• Default delay of a Cisco serial interface is 20,000 microseconds , that of a T1line.

• IGRP metric uses the sum of all of the delays of all of the outbound interfaces

to the destination network.

Metric Calculation




Changing the delay informational parameter:

The delay can be changed using: Router(config-if)# delay tens-of- µ S

(microseconds)

Example of changing the delay on a serial interface to 30,000microseconds :Router(config-if)# delay 3000

To restore the 20,000 microsecond default value:Router(config-if)# no delay

Metric Calculation

l l




IGRP

• bandwidth = (10,000,000/ bandwidth )• delay = delay /10

Note: EIGRP• bandwidth = (10,000,000/ bandwidth ) * 256• delay = ( delay /10) * 256

Note: The reference-bandwidth

For both IGRP and EIGRP: 10 7, (10,000,000/bandwidth kbps), whereas

with OSPF it was 10 8 (100,000,000/bandwidth)

The difference :• IGRP metric is 24 bits long• EIGRP metric is 32 bits long• EIGRP metric is 256 times greater for the same route• EIGRP allows for finer comparison of potential routes

Metric Calculation

IGRP M t i




Media

BandwidthK= kilobits

BW IGRP

10,000,000/Bandwidth DelayDLY IGRP

Delay/10

100M ATM 100,000K 100 100 µ S 10Fast Ethernet 100,000K 100 100 µ S 10FDDI 100,000 100 100 µ S 10

HSSI 45,045K 222 20,000 µ S 2,00016M Token Ring 16,000K 625 630 µ S 63Ethernet 10,000K 1,000 1,000 µ S 100T1 (Serial Default) 1,544K 6,476 20,000 µ S 2,000512K 512K 19,531 20,000 µ S 2,000DS0 64K 156,250 20,000 µ S 2,00056K 56K 178,571 20,000 µ S 2,000

BW IGRP and DLY IGRP display values as sent in IGRP updates and used in calculatingthe IGRP metric.

IGRP Metrics

Values displayed in show interfacecommands and sent in routing updates.

Calculated values (cumulative) displayed in routing table(show ip route). EIGRP values are 256 times greater.

M i C l l i




Router> show interfaces s1/0Serial1/0 is up, line protocol is up

Hardware is QUICC SerialDescription: Out to VERIOInternet address is 207.21.113.186/30

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,rely 255/255, load 246/255

Encapsulation PPP, loopback not setKeepalive set (10 sec)

<output omitted>

bandwidth delay

reliability load

Metric Calculation

F C bl 172 20 40 0/24




Casablanca Teheran Quebec

Yalta

172.25.1.0/24172.20.4.0/24172.20.2.0/24

172.20.40.0/24

Legend :BandwidthDelay

1,000100

1,000100

1,000100 6,4762,000

6,4762,000

19,531

2,000

19,531

2,000

1,000100

172.20.20.0/24Bandwidth (lowest or minimum)slowest bandwidth: Quebec= 19,531

Delay (sum of outgoing interfaces)= 100+2,000+2,000+100= 4,200

Metric = 19,531 + 4,200= 23,731

Using the Calculated Values

From Casablanca to 172.20.40.0/24

F C bl 172 20 40 0/24




Using BW IGRP and DLY IGRP to calculate the IGRP metric:

The slowest bandwidth has the highest BW IGRP value.

IGRP metric= highest BW IGRP + total of the DLY IGRP

= 19,531 + (100 + 2,000 + 2,000 + 100)= 19,531 + 4,200

= 23,731




Calculating the IGRP MetricUsing the

Raw Values:Bandwidth and Delay

F C bl t 172 20 40 0/24




C a s a b la n c a T e h e r a n Q u e b e c

Y a l ta

1 7 2 . 2 5 . 1 . 0 / 2 41 7 2 . 2 0 . 4 . 0 / 2 41 7 2 . 2 0 . 2 . 0 / 2 4

1 7 2 . 2 0 . 4 0 . 0 / 2 4

L e g e n d:B a n d w i d t hD e l a y

1 0 , 0 0 0 K1 , 0 0 0 u S

1 0 , 0 0 0 K1 , 0 0 0 u S

1 0 , 0 0 0 K1 , 0 0 0 u S

1 , 5 4 4 K2 0 , 0 0 0 u S

1 , 5 4 4 K2 0 , 0 0 0 u S

5 1 2 K

2 0 , 0 0 0 u S

5 1 2 K

2 0 , 0 0 0 u S

1 0 , 0 0 0 K1 , 0 0 0 u S

1 7 2 . 2 0 . 2 0 . 0 / 2 4B a n d w i d t h( l o w e s t o r m i n i m u m )l o w e s t b a n d w i d t h = 5 1 2= 1 0 , 0 0 0 , 0 0 0 / 5 1 2= 1 9 , 5 3 1

D e l a y( s u m o f o u t g o in g i n t e r f a c e s )= ( 1 , 0 0 0 / 1 0 ) + ( 2 0 , 0 0 0 / 1 0 ) +

( 2 0 , 0 0 0 / 1 0 ) + ( 1 , 0 0 0 / 1 0 )= 4 2 , 0 0 0 / 1 0= 4 , 2 0 0

M e t r i c= 1 9 , 5 3 1 + 4 , 2 0 0= 2 3 , 7 3 1

U s i n g t h e R a w V a l u e s


C l l ti B d idth




So how is Bandwidth, BW IGRP , calculated?

• The bandwidth metric is calculated by taking 10 7 (10,000,000)and dividing it by the slowest bandwidth metric along the route tothe destination.

• This is known as taking the inverse of the bandwidth scaled by afactor of 10 7 (10,000,000)

The lowest bandwidth on the route is 512K or 512 (measured inkilobits), the outgoing interface of the Quebec router.

Divide 10,000,000 by 512 and you get the bandwidth!

Bandwidth = 10,000,000/512= 19,531

Which is the lowest BW IGRP along the route

Calculating Bandwidth

C l l ti g D l




So how is Delay, DLY IGRP , calculated?

• Delay is the total sum of delays on the outgoing interfaces, in 10-microsecond units

• The sum of the delays on each of the outgoing interfaces betweenCasablanca and Yalta, from 172.20.1.0/24 through 172.20.40.0/24 is:

• 1,000 (Casablanca) + 20,000 (Teheran) + 20,000 (Quebec) + 1,000

(Yalta) = 42,000

We need this in 10-microsecond units:= (1,000/10)+(20,000/10) + (20,000/10) + (1,000/10)= 100 + 2,000 + 2,000 + 100

or = (1,000 + 20,000 + 20,000 +1,000) / 10

In either case the total sum is: Delay = 4,200

Which is the total of the DLY IGRP , the total Delays along the route!

Calculating Delay

Sl t B d idth + S f D l




IGRP metric = Bandwidth + Delay

IGRP metric = 19,531 + 4,200= 23,731

IF we were using RIP, the RIP metric would be 3 hops .

Slowest Bandwidth + Sum of Delays

sho ip ro te 172 20 40 0




Casablanca# show ip route 172.20.40.0

Known via igrp 1, distance 100, metric 23,731…172.20.1.2, from 172.20.1.2 on Ethernet 0Route metric is 23,731Total delay is 42,000 microseconds,

minimum bandwidth is 512 Kbit...

• Not to be redundant, but if we were using RIP, theRIP metric would be 3 hops.

show ip route 172.20.40.0



So, what about Reliability andLoad?

Reliability and Load




The metrics used by EIGRP in making routing decisions are (lower the

metric the better):• bandwidth• delay• load

• reliability

By default, EIGRP uses only:• Bandwidth• Delay






Reliability

• Reliability is measure dynamically• Uses error rate for measurement• Reflects the total outgoing error rates of the interfaces along the

route

• Calculated on a five minute weighted average, so not to allowsudden peaks and valleys to make a significant impact

Expressed as an 8 bit number • 255 is a 100% reliable link

• 1 is a minimally reliable link

Higher the better!






shows reliability as a fraction of 255, for example:rely 190/255 (or 74% reliability)rely 234/255 (or 92% reliability)rely 255/255 (or 100% reliability)

Router> show interfaces s1/0

Serial1/0 is up, line protocol is upHardware is QUICC SerialDescription: Out to VERIOInternet address is 207.21.113.186/30MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,


<output omitted>

bandwidth delay

reliability load






Load

• Load is measure dynamically• Uses channel occupancy for measurement• Reflects the total outgoing load of the interfaces along the route• Calculated on a five minute weighted average, so not to allow sudden

peaks and valleys to make a significant impact

Expressed as an 8 bit number • 255 is a 100% loaded link• 1 is a minimally loaded link Lower the better!

Note: Even though load and reliability are dynamically changing values,EIGRP will not recalculate the route metric when these parameterschange.






shows load as a fraction of 255, for example:load 10/255 (or 3% loaded link)load 40/255 (or 16% loaded link)load 255/255 (or 100% loaded link)

Router> show interfaces s1/0

Serial1/0 is up, line protocol is upHardware is QUICC SerialDescription: Out to VERIOInternet address is 207.21.113.186/30MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,


<output omitted>

bandwidth delay

reliability load






IGRP metric =

[k1* BW IGRP(minimum) +(k2* BW IGRP(minimum) )/(256- LOAD ) +

k3* DLY IGRP(sum) ] *

[k5/RELIABILITY + k4)]• k2 metric effects LOAD• k4 and k5 effects RELIABILITY• Multiply Reliability only if > 0

Default :k1=k3=1 and k2=k4=k5=0

• You may change the k values to change what you want to give more or less weight to.

– k1 for bandwidth – k2 for load – k3 for delay – k4 and k5 for Reliability

• Higher the k value, the more that part of the metric is used to calculate the overall IGRP

metric






Turning the knobs:

We can use the other metrics of Reliability and Load by adjusting their k valuesto something greater than “0”

The command to adjust the k values is:Router(config-router)# metric weights tos k1 k2 k3 k4 k5

Notes :• tos is always set to 0; at one time it was Cisco’s intent to use it, but it was

never implemented• EIGRP neighbors must agree on K values to establish an adjacency and to

avoid routing loops.

Caution!• Know what the impact will be before changing the defaults.• It can give you unexpected results if you do not know what you are doing!• If you modify the weights, you should configure all routers so they are all using

the same weight values.


IGRP and EIGRP: A migration path




IGRP and EIGRP: A migration path

Automatic redistribution between IGRP and EIGRP as long as “AS” numbers are the same.

Outside routes (redistributed) are tagged asexternal routes.

No differentiation between internal andexternal routes.

Maximum Hop Count = 224Maximum Hop Count = 255

bandwidth = (10,000,000/ bandwidth kbps ) * 256delay = ( delay /10) * 256

32 bit metric for bandwidth and delay

bandwidth = (10,000,000/ bandwidth kbps )delay = delay /10

24 bit metric for bandwidth and delay

Classless Routing Protocol• VLSM, CIDR

Classful Routing Protocol

EIGRPIGRP



Ch. 7 – Distance Vector Routing ProtocolsPart 2 of 2: Distance Vector Routing and

IGRP

CCNA version 1.0Rick Graziani

Cabrillo College

distance vactor routing protocol igrp

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