• IGRP
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IGRP
'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.
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IGRP
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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.
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IGRP
IGRP is considered a
Classful network|classful
routing protocol
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IGRP - Advancement
In the new Cisco CCNA curriculum
(version 4), IGRP is mentioned only briefly,
as an obsolete protocol.
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Enhanced Interior Gateway Routing Protocol - EIGRP composite and vector
metrics
EIGRP associates six different vector
metrics with each route and considers only
four of the vector metrics in computing the
Composite metric:
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Enhanced Interior Gateway Routing Protocol - EIGRP composite and vector
metrics
;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.
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EIGRP
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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/i
osswrel/ps6537/ps6554/ps6599/ps6630/qa_
C67-726299.html Enhanced Interior Gateway
Routing Protocol (EIGRP) Informational RFC
Frequently Asked Questions], retrieved 14
September 2013
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EIGRP
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.
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EIGRP - Overview
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The Enhanced Interior Gateway Routing Protocol
replaced the Interior Gateway Routing Protocol
(IGRP) in
1993.[http://www.differencebetween.net/technolog
y/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.
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EIGRP - Overview
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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.
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EIGRP - Overview
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In addition to the routing table, EIGRP uses the
following tables to store information:
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EIGRP - Overview
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Active indicates that EIGRP is still trying to calculate
the best path for the specific route
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EIGRP - Overview
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This behavior is more inline with link-state
routing protocols, thus EIGRP is mostly
considered a hybrid protocol.
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EIGRP - Overview
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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.
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EIGRP - Features
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EIGRP supports the
following features:
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EIGRP - Features
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* Backwards compatibility with the IGRP
routing
protocols.[http://www.cisco.com/en/US/tec
h/tk365/technologies_tech_note09186a00
80093f07.shtml Introduction to EIGRP].
Cisco. Retrieved on 2014-05-30.
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EIGRP - Cisco IOS example
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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.
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EIGRP - Technical details
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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/col
lateral/ios-nx-os-software/enhancedinterior-gateway-routing-protocoleigrp/whitepaper_C11-720525.html
Enhanced Interior Gateway Routing
Protocol (EIGRP) Wide Metrics], retrieved
14 March 2014
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EIGRP - Technical details
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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 EIGRPenabled router outside the autonomous
system has a default administrative distance
of 170.Cisco Systems (2013),
[http://www.cisco.com/en/US/tech/tk365/tech
nologies_tech_note09186a0080094195.shtml
What is Administrative Distance?], retrieved
14 September 2013
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EIGRP - Technical details
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EIGRP uses List of IP
protocol
numbers|protocol
number 88.
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EIGRP - Distance vector routing protocol
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EIGRP a fast routing protocol
based on distance vectors
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EIGRP - Routing metric
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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.
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EIGRP - Routing metric
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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.
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EIGRP - Routing metric
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EIGRP scales the interface Bandwidth and Delay
configuration values with following calculations:
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EIGRP - Routing metric
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EIGRP takes this value directly
without scaling into the weighted
formula
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EIGRP - Routing metric
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.
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EIGRP - Feasible successor
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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.
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EIGRP - Feasibility condition
The feasibility condition is a sufficient
condition for loop freedom in EIGRProuted 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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