Ch. 7 – Distance Vector Routing Protocols
Part 2 of 2: Distance Vector Routing and
IGRP
CCNA version 1.0
Rick Graziani
Cabrillo College
Note to instructors
• If you have downloaded this presentation from the Cisco Networking
Academy Community FTP Center, this may not be my latest version of
this PowerPoint.
• For the latest PowerPoints for all my CCNA, CCNP, and Wireless
classes, 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 graziani@cabrillo.edu (I really don’t
mind helping.) Also, if you run across any typos or errors in my
presentations, please let me know.
• I will add “(Updated – date)” next to each presentation on my web site
that has been updated since these have been uploaded to the FTP
center.
Thanks! Rick
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2
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
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IGRP Features
• By default, the IGRP routing protocol uses bandwidth and delay as
•
•
metrics.
Additionally, IGRP can be configured to use a combination of variables
to determine a composite metric.
Those variables include:
– Bandwidth
– Delay
– Load
– Reliability
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IGRP Metrics
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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 routing
metric.
IGRP has an administrative distance of 100, more “trustworthy” than
RIP at 120.
• This means a Cisco router will prefer an IGRP learned route over a RIP
learned route to the same network.
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6
Administrative Distances
Cisco Default Administrative Distances
Route Source
Connected interface
Administrative Distance
0
Static Route
1
EIGRP summary route
5
External BGP
20
EIGRP
90
IGRP
100
OSPF
110
IS-IS
115
RIP
120
EGP
140
External EIGRP
170
Internal BGP
200
Unknown
255
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IGRP Metrics
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8
IGRP Routes
• Interior
•
•
•
•
“Interior routes are routes between subnets of a network attached to a
router 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.
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IGRP Routes
• System
“System routes are routes to networks within an autonomous system.
The Cisco IOS software derives system routes from directly connected
network interfaces and system route information provided by other
IGRP-speaking routers or access servers. System routes do not include
subnet information.”
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10
IGRP Routes
• Exterior
“Exterior routes are routes to networks outside the autonomous system
that are considered when identifying a gateway of last resort. The Cisco
IOS 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 a
connected network. If the autonomous system has more than one
connection to an external network, different routers can choose different
exterior routers as the gateway of last resort.”
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11
IGRP Timers
• IGRP has a number of features that are designed to enhance its
stability, such as:
– Holddowns
– Split horizons
– Poison reverse updates
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IGRP
Timers
Update timer
• The update timer specifies how frequently routing update messages
•
•
•
should 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.
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IGRP
Timers
Invalid timer
• The invalid timer specifies 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 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 the
Rick
Graziani graziani@cabrillo.edu
routing
table until the flush timer expires.”
14
IGRP
Timers
Holddown
timer
• The holddown timer specifies the amount of time for which
•
•
•
information about poorer routes are ignored.
Zinin: “Holddown specifies the number of seconds that a route must
spend 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 as
unreachable, until the flush timer expires.
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IGRP
Timers
Flush timer
•
•
•
•
•
•
Finally, the flush timer indicates how much time should pass before a route is
flushed 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.
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IGRP Timers
Update
90 secs – Update and Invalid timers are then reset.
Invalid
270 secs - Invalid timer expires, route now
“unreachable” but still in routing table until flush timer
expires. Holddown timer of 280 sec begins.
280 secs – Holddown timer
Holddown
expires, will now accept a poorer route to
same network. Still in routing table
630 secs –
Flush
My testing shows that the flush timer starts
after the first 90 second update is missed.
•
•
•
•
Route will now be
removed from the
routing table.
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 the
routing table
Holddown timer: specifies the amount of time for which information about poorer routes
are ignored.
Flush timer: how much time should pass before a route is flushed from the routing table
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IGRP
Timers
• 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 length
subnet masks (VLSM).
Enhanced IGRP (EIGRP) supports VLSM.
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Configuring IGRP
•
•
Same network commands as RIP.
IGRP “AS” number must be the same on all routers.
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Configuring IGRP
Router(config-router)#router igrp 100
Router(config-router)#timers basic update invalid holddown
flush [sleeptime]
Router(config-router)# no timers basic
timers basic (IGRP)
• To adjust Interior Gateway Routing Protocol (IGRP)
network timers, use the timers basic router configuration
command. To restore the default timers, use the no form of
this command.
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Migrating from RIP to IGRP
Router(config)#router rip
Router(config-router)#network
Router(config-router)#network
Router(config-router)#exit
Router(config)#router igrp 10
Router(config-router)#network
Router(config-router)#network
Router(config-router)#exit
Router(config)#no router rip
•
•
172.16.0.0
192.168.1.0
172.16.0.0
192.168.1.0
Enable IGRP
Suggestion: Remove RIP configuration from routers even
though the administrative distance will prefer RIP
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Verifying IGRP
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Verifying IGRP
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Verifying IGRP
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Verifying IGRP
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Verifying IGRP
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Troubleshooting IGRP
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Troubleshooting IGRP
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Troubleshooting IGRP
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Domains…
Rick’s extra information on autonomous systems…(FYI
only!)
Two types of autonomous systems:
1. Process domain
2. Routing domain
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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 process
domains.
Redistribution is used to route between these types of
autonomous systems.
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31
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 used
to route between these types of autonomous systems.
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Two Types of Autonomous Systems:
Process Domains and Routing Domains
Process Domain
Process Domain
Router
Router
Router
BGP
Router
Router
Router
Router
Router
Router
Router
IGRP 30
Router
IGRP 40
AS 90
Routing Domain
AS 10
Routing Domain
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Summary
But there is still more!
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IGRP Metric Information (and for
EIGRP as well!)
Metric Calculation
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 pipe
and
delay as the length of the pipe.
•
•
Bandwidth is a the carrying capacity
Delay is the end-to-end travel time.
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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 interface
that is routing EIGRP.
• These are the raw values.
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Metric Calculation
Router> show interfaces s1/0
Serial1/0 is up, line protocol is up
delay
bandwidth
Hardware is QUICC Serial
Description: Out to VERIO
Internet 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 set
Keepalive set (10 sec)
<output omitted>
reliability
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load
38
Metric Calculation (Review)
–
–
–
–
EIGRP
bandwidth is in kbps
Rick Graziani graziani@cabrillo.edu
k1 for bandwidth
k2 for load
k3 for delay
k4 and k5 for Reliability
Router(config-router)# metric
weights tos k1 k2 k3 k4 k5
IGRP
Viva la
difference!
Media
100M ATM
Fast Ethernet
FDDI
HSSI
16M Token Ring
Ethernet
T1 (Serial Default)
512K
DS0
56K
Bandwidth
K= kilobits
100,000K
100,000K
100,000
45,045K
16,000K
10,000K
1,544K
512K
64K
56K
BWIGRP
10,000,000/Bandwidth
100
100
100
222
625
1,000
6,476
19,531
156,250
178,571
DLYIGRP
Delay
Delay/10
100 S
100 S
100 S
20,000 S
630 S
1,000 S
20,000 S
20,000 S
20,000 S
20,000 S
10
10
10
2,000
63
100
2,000
2,000
2,000
2,000
BWIGRP and DLYIGRP display values as sent in IGRP updates and used in calculating
the IGRP metric.
EIGRP
Media
Bandwidth
K= kilobits
BWEIGRP
10,000,000/Bandwidth
*256
Calculated values
(cumulative) displayed
in routing table (show
ip route).
EIGRP values are 256
times greater.
100M ATM
Fast Ethernet
FDDI
HSSI
16M Token Ring
Ethernet
T1 (Serial
Default)
512K
DS0
56K
DLYEIGRP
Delay
Delay/10
*256
100,000K
100,000K
100,000K
45,045K
16,000K
10,000K
1,544K
25,600
25,600
25,600
56,832
160,000
256,000
1,657,856
100 S
100 S
100 S
20,000 S
630 S
1,000 S
20,000 S
2,560
2,560
2,560
512,000
16,128
25,600
512,000
512K
64K
56K
4,999,936
40,000,000
45,714,176
20,000 S
20,000 S
20,000 S
512,000
512,000
512,000
BWEIGRP and DLYEIGRP display values as sent in EIGRP updates and used in
calculating the EIGRP metric.
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Displaying Interface Values
Router> show interface s0/0
Serial0/0 is up, line protocol is up
Hardware is QUICC Serial
Bandwidth
Delay
Description: Out to VERIO
Internet 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 set
Keepalive set (10 sec)
<output omitted>
Reliability
Load
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)
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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 s0/0
Serial0/0 is up, line protocol is up
Hardware is QUICC Serial
Bandwidth
Delay
Description: Out to VERIO
Internet 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 set
Keepalive set (10 sec)
<output omitted>
Reliability
Load
Routing Table Metric
• Default: Slowest of bandwidth plus the sum of the delays of
all outgoing interfaces from “this router” to the destination
network.
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Metric Calculation
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 1,544,000
bps (T1), whether that interface is attached to a T1 line (1.544 Mbps) or a 56K
line.
•
IGRP metric uses the slowest bandwidth of all of the outbound interfaces to
the destination network.
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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
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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, 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 T1
line.
•
IGRP metric uses the sum of all of the delays of all of the outbound interfaces
to the destination network.
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Metric Calculation
Changing the delay informational parameter:
The delay can be changed using:
Router(config-if)# delay tens-of- S
(microseconds)
Example of changing the delay on a serial interface to 30,000
microseconds:
Router(config-if)# delay 3000
To restore the 20,000 microsecond default value:
Router(config-if)# no delay
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Metric Calculation
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: 107, (10,000,000/bandwidth kbps), whereas
with OSPF it was 108 (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
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IGRP Metrics
Values displayed in show interface
commands and sent in routing updates.
Media
Bandwidth
K= kilobits
100M ATM
Fast Ethernet
FDDI
HSSI
16M Token Ring
Ethernet
T1 (Serial Default)
512K
DS0
56K
100,000K
100,000K
100,000
45,045K
16,000K
10,000K
1,544K
512K
64K
56K
BWIGRP
10,000,000/Bandwidth
100
100
100
222
625
1,000
6,476
19,531
156,250
178,571
DLYIGRP
Delay
100 S
100 S
100 S
20,000 S
630 S
1,000 S
20,000 S
20,000 S
20,000 S
20,000 S
Delay/10
10
10
10
2,000
63
100
2,000
2,000
2,000
2,000
BWIGRP and DLYIGRP display values as sent in IGRP updates and used in calculating
the IGRP metric. Calculated values (cumulative) displayed in routing table
(show ip route). EIGRP values are 256 times greater.
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Metric Calculation
Router> show interfaces s1/0
Serial1/0 is up, line protocol is up
delay
bandwidth
Hardware is QUICC Serial
Description: Out to VERIO
Internet 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 set
Keepalive set (10 sec)
<output omitted>
reliability
Rick Graziani graziani@cabrillo.edu
load
49
From Casablanca to 172.20.40.0/24
Using the Calculated Values
1,000
100
1,000
100
172.20.4.0/24
1,000
100
6,476
2,000
6,476
2,000
172.25.1.0/24
Casablanca
Bandwidth (lowest or minimum)
slowest bandwidth: Quebec
= 19,531
Delay (sum of outgoing interfaces)
= 100+2,000+2,000+100
= 4,200
Teheran
Legend:
Bandwidth
Delay
172.20.2.0/24
Quebec
19,531
2,000
172.20.20.0/24
19,531
2,000
172.20.40.0/24
Yalta
Metric = 19,531 + 4,200
= 23,731
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1,000
100
50
From Casablanca to 172.20.40.0/24
Using BWIGRP and DLYIGRP to calculate the IGRP metric:
The slowest bandwidth has the highest BWIGRP value.
IGRP metric
= highest BWIGRP + total of the DLYIGRP
= 19,531 + (100 + 2,000 + 2,000 + 100)
= 19,531 + 4,200
= 23,731
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Calculating the IGRP Metric
Using the
Raw Values:
Bandwidth and Delay
From Casablanca to 172.20.40.0/24
Using the Raw Values
10,000K
1,000uS
10,000K
1,000uS
172.20.4.0/24
10,000K
1,000uS
1,544K
20,000uS
1,544K
20,000uS
172.25.1.0/24
Casablanca
Bandwidth (lowest or minimum)
lowest bandwidth = 512
= 10,000,000/512
= 19,531
Delay (sum of outgoing interfaces)
= (1,000/10) + (20,000/10) +
(20,000/10) + (1,000/10)
= 42,000/10
= 4,200
Metric = 19,531 + 4,200
23,731
Rick Graziani=graziani@cabrillo.edu
Teheran
Legend:
Bandwidth
Delay
172.20.2.0/24
Quebec
512K
20,000uS
172.20.20.0/24
512K
20,000uS
172.20.40.0/24
Yalta
10,000K
1,000uS
53
Calculating Bandwidth
So how is Bandwidth, BWIGRP, calculated?
• The bandwidth metric is calculated by taking 107 (10,000,000)
and dividing it by the slowest bandwidth metric along the route to
the destination.
• This is known as taking the inverse of the bandwidth scaled by a
factor of 107 (10,000,000)
The lowest bandwidth on the route is 512K or 512 (measured in
kilobits), 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 BWIGRP along the route
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Calculating Delay
So how is Delay, DLYIGRP, calculated?
• Delay is the total sum of delays on the outgoing interfaces, in 10microsecond units
• The sum of the delays on each of the outgoing interfaces between
Casablanca 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 DLYIGRP, the total Delays along the route!
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Slowest Bandwidth + Sum of Delays
IGRP metric = Bandwidth + Delay
IGRP metric = 19,531 + 4,200
= 23,731
IF we were using RIP, the RIP metric would be 3 hops.
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show ip route 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 0
Route metric is 23,731
Total delay is 42,000 microseconds,
minimum bandwidth is 512 Kbit
...
•
Not to be redundant, but if we were using RIP, the
RIP metric would be 3 hops.
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57
So, what about Reliability and
Load?
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
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Reliability and Load
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 allow
sudden 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!
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Reliability and Load
Router> show interfaces s1/0
Serial1/0 is up, line protocol is up
delay
bandwidth
Hardware is QUICC Serial
Description: Out to VERIO
Internet 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 set
Keepalive set (10 sec)
<output omitted>
reliability
load
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)
Rick Graziani graziani@cabrillo.edu
61
Reliability and 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 parameters
change.
Rick Graziani graziani@cabrillo.edu
62
Reliability and Load
Router> show interfaces s1/0
Serial1/0 is up, line protocol is up
delay
bandwidth
Hardware is QUICC Serial
Description: Out to VERIO
Internet 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 set
Keepalive set (10 sec)
<output omitted>
reliability
load
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)
Rick Graziani graziani@cabrillo.edu
63
Reliability and Load
IGRP metric =
[k1* BWIGRP(minimum) +
(k2* BWIGRP(minimum))/(256-LOAD) +
k3* DLYIGRP(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
Rick Graziani graziani@cabrillo.edu
64
Reliability and Load
Turning the knobs:
We can use the other metrics of Reliability and Load by adjusting their k values
to 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.
Rick Graziani graziani@cabrillo.edu
65
IGRP and EIGRP: A migration path
IGRP
EIGRP
Classful Routing Protocol
Classless Routing Protocol
• VLSM, CIDR
bandwidth = (10,000,000/bandwidth kbps)
delay
= delay/10
24 bit metric for bandwidth and delay
bandwidth = (10,000,000/bandwidth kbps) * 256
delay
= (delay/10) * 256
32 bit metric for bandwidth and delay
Maximum Hop Count = 255
Maximum Hop Count = 224
No differentiation between internal and
external routes.
Outside routes (redistributed) are tagged as
external routes.
Automatic redistribution between IGRP and EIGRP as long as “AS” numbers are the same.
Rick Graziani graziani@cabrillo.edu
Ch. 7 – Distance Vector Routing Protocols
Part 2 of 2: Distance Vector Routing and
IGRP
CCNA version 1.0
Rick Graziani
Cabrillo College