IGRP

IGRP (Interior Gateway Routing Protocol)

The Interior Gateway Routing Protocol (IGRP) is a Cisco proprietary protocol. So to use IGRP protocol we must have only Cisco routers. Cisco created this routing protocol to overcome some inabilities’ in RIP.

Features of IGRP:

• IGRP is a Cisco proprietary protocol.
• IGRP is a distance-vector interior routing protocol.
• AD no# is 100.
• IGRP has a maximum default hop count of 100# routers. And hop count can be extended to 255 routers.(whereas RIP has hop count of only15 routers.)
• IGRP supports 4 equal paths and 2 unequal paths for Load Balancing.
• IGRP supports Autonomous System (AS) number.
• Metric is Bandwidth and delay of line which is also called composite metric.reliabilty, load and MTU is also used occasionally but not as default.

· MTUàMaximumTransferUnit is used to define data size of an IGRP frame.

Difference between RIP & IGRP

RIP	IGRP
RIP does not use autonomous system number.	IGRP uses an autonomous system number.
RIP can be used only in smaller networks.	IGRP can be completely utilised in larger networks.
Full route table updates is issued for every 30 seconds.	Full route table updates is issued for every 90 seconds.
RIP uses hop count as metric with maximum count of only 15 routers.	IGRP uses bandwidth and delay of line as metric.
Administrative distance is 120#.	Administrative distance is 100#.

To optimise the performance of network, IGRP uses different kind of timers as mentioned in the table below,

Router Timer	Description	Time in Seconds
Hello timer (or) Update Timers	It specifies how frequently routing messages will be sent	90 seconds
Invalid Timer	It specifies how long a router should wait in the absence of a routing-update message of a specific route before declaring it invalid	Three times the Update timer, 270 seconds
Hold-down Timer	It specifies the hold-down period	three times the update timer + 10 seconds=280 seconds
Flush Timer	It indicates how much time should pass before an IGRP route is flushed from the routing table.	Seven times the routing update period, 630 seconds.

IGRP Configurations

Syntax

Router # config t

Router (config) #router igrp (autonomous number)

Router (config) #network (directly connected network)

The AS number parameter specifies the autonomous system number that is supported by this IGRP process and allows multiple IGRP processes to run on a single router. The AS number range varies between 1 and 65,655.Like RIP in IGRP also we have to configure only the directly connected network.

Other commands for Configuring, Monitoring and Verifying IGRP are as follows:

Command	Description
Show ip protocols	Shows routing protocol parameters and current timer values
Debug ip igrp transactions	Issues log messages with details of the IGRP updates.
Debug ip igrp events	Issues log messages for each igrp updates
Ping	Sends and receive ICMP echo messages to verify connectivity
trace	Sends a series of ICMP echoes with increasing TTL value
Show ip route	Shows routing protocol parameters and current timer values

Example

Configure IGRP between two routers shown in the picture below who’s IP address are as follows

LONDON: 192.168.1.10

PARIS: 192.168.1.50

Configurations:

London # config t

London (config) #router igrp 10

London (config) #network 192.168.1.0

Paris # config t

Paris (config) #router igrp 10

Paris (config) #network 192.168.1.0