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 |
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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
