Interior Gateway Routing Protocol (IGRP) is a
distance vector
A distance-vector routing protocol in data networks determines the best route for data packets based on distance. Distance-vector routing protocols measure the distance by the number of routers a packet has to pass; one router counts as one hop. ...
interior gateway protocol (IGP) developed by
Cisco. It is used by
routers to exchange
routing
Routing is the process of selecting a path for traffic in a network or between or across multiple networks. Broadly, routing is performed in many types of networks, including circuit-switched networks, such as the public switched telephone netw ...
data within an
autonomous system Autonomous system may refer to:
* Autonomous system (Internet), a collection of IP networks and routers under the control of one entity
* Autonomous system (mathematics), a system of ordinary differential equations which does not depend on the inde ...
.
IGRP is a
proprietary protocol. IGRP was created in part to overcome the limitations of
RIP (maximum hop count of only 15, and a single routing metric) when used within large networks. IGRP supports multiple metrics for each route, including
bandwidth,
delay,
load, and
reliability
Reliability, reliable, or unreliable may refer to:
Science, technology, and mathematics Computing
* Data reliability (disambiguation), a property of some disk arrays in computer storage
* High availability
* Reliability (computer networking), ...
; to compare two routes these metrics are combined into a single metric, using a formula which can be adjusted through the use of pre-set constants. By default, the IGRP composite metric is a sum of the segment delays and the lowest segment bandwidth. The maximum configurable hop count of IGRP-routed packets is 255 (default 100), and routing updates are
broadcast
Broadcasting is the distribution (business), distribution of sound, audio or video content to a dispersed audience via any electronic medium (communication), mass communications medium, but typically one using the electromagnetic spectrum (radio ...
every 90 seconds (by default). IGRP uses
protocol number 9 for communication.
[{{cite web
, url=https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xml
, title=Assigned Internet Protocol Numbers
, publisher= Internet Assigned Numbers Authority (IANA)
, access-date=18 June 2013]
IGRP is considered a
classful routing protocol. Because the protocol has no field for a
subnet mask, the router assumes that all subnetwork addresses within the same Class A, Class B, or Class C network have the same subnet mask as the subnet mask configured for the interfaces in question. This contrasts with classless routing protocols that can use
variable length subnet masks. Classful protocols have become less popular as they are wasteful of
IP address space.
Advancement
In order to address the issues of address space and other factors, Cisco created
EIGRP (Enhanced Interior Gateway Routing Protocol). EIGRP adds support for
VLSM (variable length subnet mask) and adds the
Diffusing Update Algorithm (DUAL) in order to improve routing and provide a loopless environment. EIGRP has completely replaced IGRP, making IGRP an obsolete routing protocol. In Cisco IOS versions 12.3 and greater, IGRP is completely unsupported. In the new Cisco
CCNA curriculum (version 4), IGRP is mentioned only briefly, as an "obsolete protocol".
References
External links
Cisco - An Introduction to IGRP
US Patent 5,088,032 "Method and apparatus for routing communications among computer networks"
Cisco protocols
Routing protocols