igrp

• IGRP

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IGRP

1 'Interior Gateway Routing Protocol' ('IGRP') is a distance-vector

routing protocol|distance vector Interior Gateway Protocol|interior

routing protocol (IGP) developed by Cisco Systems, Inc.|Cisco. It is used

by Router (computing)|routers to exchange routing data within an autonomous system (Internet)|

autonomous system.https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

IGRP

1 The maximum hop count of IGRP-routed packets is 255 (default 100),

and routing updates are Broadcasting (computing)|broadcast

every 90 seconds (by default).[

http://www.cisco.com/en/US/docs/ios/12_2/ip/configuration/guide/1cfigrp.html Cisco Systems] Configuring IGRP

IGRP uses port number 9 for communication.


IGRP

1 IGRP is considered a Classful network|classful

routing protocol


IGRP - Advancement

1 In the new Cisco CCNA curriculum (version 4), IGRP is mentioned only

briefly, as an obsolete protocol.


Enhanced Interior Gateway Routing Protocol - EIGRP composite and vector metrics

1 EIGRP associates six different vector metrics with each route and

considers only four of the vector metrics in computing the Composite

metric:


Enhanced Interior Gateway Routing Protocol - EIGRP composite and vector metrics

1 ;Hop Count: Number of routers a packet passes through when routing to a remote

network, used to limit the EIGRP AS. EIGRP maintains a hop count for every route,

however, the hop count is not used in metric calculation. It is only verified against a

predefined maximum on an EIGRP router (by default it is set to 100 and can be changed to any value between 1 and 255). Routes having a hop count higher than the maximum will be advertised as unreachable by an EIGRP router.


EIGRP

1 The protocol was designed by Cisco Systems as a proprietary protocol, available only on Cisco routers, but Cisco converted it to an open standard in 2013.Cisco Systems

(2013), [http://www.cisco.com/en/US/prod/collateral/

iosswrel/ps6537/ps6554/ps6599/ps6630/qa_C67-726299.html Enhanced Interior

Gateway Routing Protocol (EIGRP) Informational RFC Frequently Asked

Questions], retrieved 14 September 2013https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

EIGRP

1 EIGRP is used on a router (computing)|router to share routes with other routers

within the same Autonomous System (Internet)|autonomous system. Unlike

other well known routing protocols, such as routing information protocol|RIP,

EIGRP only sends incremental updates, reducing the workload on the router and

the amount of data that needs to be transmitted.


EIGRP - Overview

1 The Enhanced Interior Gateway Routing Protocol replaced the Interior Gateway Routing Protocol

(IGRP) in 1993.[http://www.differencebetween.net/technology/internet/difference-between-igrp-and-eigrp IGRP and EIGRP | Difference Between | IGRP vs

EIGRP]. Difference Between (2011-05-19). Retrieved on 2014-05-30. One of the major

reasons for this was because the design of the Internet Protocol had been changed to support IPv4 address|classless IPv4 addresses, which

IGRP could not support.https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

EIGRP - Overview

1 Almost all router (computing)|routers contain a routing table that contains rules

by which traffic is forwarded in a network. If the router does not contain a valid path to

the destination, the traffic is discarded. EIGRP is a dynamic routing protocol by which routers automatically share route

information. This eases the workload on a network administrator who does not have to

configure changes to the routing table manually.


EIGRP - Overview

1 In addition to the routing table, EIGRP uses the following tables to store information:


EIGRP - Overview

1 Active indicates that EIGRP is still trying to calculate the best path for the specific route


EIGRP - Overview

1 This behavior is more inline with link-state routing protocols, thus

EIGRP is mostly considered a hybrid protocol.


EIGRP - Overview

1 When a router (computing)|router running EIGRP is connected to

another router also running EIGRP, information is exchanged between

the two routers and a relationship is formed known as an adjacency. The

entire routing table is exchanged between both routers at this time.

After this has occurred, only differential changes are sent.


EIGRP - Features

1 EIGRP supports the following features:


EIGRP - Features

1 * Backwards compatibility with the IGRP routing

protocols.[http://www.cisco.com/en/US/tech/tk365/technologies_tech_note

09186a0080093f07.shtml Introduction to EIGRP]. Cisco.

Retrieved on 2014-05-30.


EIGRP - Cisco IOS example

1 Example of setting up EIGRP on a Cisco IOS router for a private network. The

0.0.15.255 wildcard character|wildcard in this example indicates a subnetwork with a maximum of 4094 hosts—it is the bitwise

complement of the subnet mask 255.255.240.0. The 'no auto-summary'

command prevents automatic route summarization on classful boundaries, which would otherwise result in routing

loops in discontiguous networks.https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

EIGRP - Technical details

1 EIGRP determines the value of the path using four metrics: bandwidth,

load, delay, and reliability.Cisco Systems (2012),

[http://www.cisco.com/c/en/us/products/collateral/ios-nx-os-software/

enhanced-interior-gateway-routing-protocol-eigrp/whitepaper_C11-720525.html Enhanced Interior

Gateway Routing Protocol (EIGRP) Wide Metrics], retrieved 14 March

2014



1 EIGRP routing information exchanged to a router from another router within the same

autonomous system has a default administrative distance of 90. EIGRP routing information that has come from an EIGRP-

enabled router outside the autonomous system has a default administrative distance of

170.Cisco Systems (2013), [http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094195.shtml What

is Administrative Distance?], retrieved 14 September 2013



1 EIGRP uses List of IP protocol numbers|

protocol number 88.


EIGRP - Distance vector routing protocol

1 EIGRP a fast routing protocol based on distance vectors


EIGRP - Routing metric

1 By default, only total delay and minimum bandwidth are considered when EIGRP is started on a router, but an administrator can enable or

disable all the K values as needed to consider the other Vector metrics.



1 Obviously, these constants must be set to the same value on all routers in an EIGRP system, or permanent

routing loops may result. Cisco routers running EIGRP will not form

an EIGRP adjacency and will complain about K-values mismatch until these values are identical on

these routers.



1 EIGRP scales the interface Bandwidth and Delay configuration values with following

calculations:



1 EIGRP takes this value directly without scaling into the

weighted formula



1 This way, redistributing information between EIGRP and IGRP involves simply dividing or multiplying the metric value by a factor of 256,

which is done automatically.


EIGRP - Feasible successor

1 Thus, every successor is also a feasible successor. However, in most references

about EIGRP the term feasible successor is used to denote only those routes which

provide a loop-free path but which are not successors (i.e. they do not provide the

least distance). From this point of view, for a reachable destination there is always at least one successor, however, there might

not be any feasible successors.


EIGRP - Feasibility condition

1 The feasibility condition is a sufficient condition for loop freedom in EIGRP-routed network. It is used to select

the successors and feasible successors that are guaranteed to be on a loop-free route to a destination. Its simplified formulation is strikingly

simple:


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