What is Interior Gateway Routing Protocol IGRP? – Interior Gateway Routing Protocol IGRP is a Dynamic Routing protocol developed by Cisco mid-1980s. IGRP is a routing protocol specific to Cisco devices only.
What is Interior Gateway Routing Protocol IGRP?

What is Interior Gateway Routing Protocol IGRP?

What is Interior Gateway Routing Protocol IGRP?

Although the IGRP and RIP routing protocols are very similar, they have different configurations. The RIP has a Maximum 16 Hop Count value, while the Maximum Hop Count value of the IGRP protocol is 255.

IGRP is a Distance Vector protocol and uses Bandwidth, Delay, Reliability, Load, and MTU (Maximum Transmission Unit) values when selecting the best route.

IGRP Administrative Distance (AD) value is 100. The RIP routing protocol is the AD value 120. IGRP gives priority over RIP. For example, if both routing protocols enable in a network environment, IGRP will have priority.

If Bandwidth is not set while configures IGRP, the default value of 1.5 Mbit Bandwith evaluates. The biggest difference between the IGRP and RIP Distance Vector protocols is the use of the Autonomous Number (AS) Number of the IGRP protocol.

The rationale for using IGRP Bandwith is to communicate over the fastest connection. In short, on two different connections with 64 Kbit and 1.5 Mbit, the router chooses the fastest connection (1.5 Mbit) and sends the packet.

In an IGRP-configured network, only Routers with the same AS number can communicate. The AS number value is determined by the user according to the network design and layout, and there is no obligation.

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IGRP Protocol Features

Let’s explain IGRP properties in order.

1. A Distance Vector protocol.
2. IGRP is a Classful protocol.
3. There is no CIDR support.
4. VLSM has no support.
5. Uses Bandwidth and Delay by default.
6. Uses Reliability and Load.
7. Send a routing table every 90 seconds.
8. The Hop Count value is 100. But it can be set up to 255.
9. Authentication There is no support.
10. Use Triggered Updates.
11. Uses Poison Reverse and Split Horizon techniques.
12. The Administrative Distance value is 100.
13. Used in large networks.

What is the Use of IGRP?

The following example of the use of IGRP Bandwidth refers to the transmission of packets over the fastest link.

What is Interior Gateway Routing Protocol IGRP?

IGRP Timers

1. Update Timer – 90 Seconds.

Sends routing updates every 90 seconds.

2. Invalid Timer – 270 Seconds.

Update Timer x 3 = Invalid Timer

If a network is not reachable, this network is the duration of being invalided from the Router’s routing table.

In short, if the router has not received an update for a route, it will wait before declaring this route invalid.

3. Hold Down Timer – 280 Seconds.

Update Timer x 3 + 10 Seconds= Hold Down Timer

If a network cannot reach or the route metric is increased, it takes to wait before adding the new route. The router does not accept a change to the route until the waiting period expires. Hold Down Timer prevents routing looping (Loop) on the network.

The Hold Down Timer is 280 seconds.

4. Flush Timer – 630 Seconds.

Update Timer x 7 = Flush Timer

The Router uses the Flush Timer to remove the invalid route from the routing table. Flush Timer is 630 seconds by default.

Difference Between IGRP and RIP

By comparing IGRP and RIP, we can better understand these routing protocols.

FeatureRIP Version 1RIP Version 2IGRP
Update Timer30 Seconds30 Seconds90 Seconds
MetricHop CountHop CountDefault: Bandwidth, Delay, Reliability, Load, MTU
VLSM SupportNoYesNo
Metric Value16164, 294, 967, 295

IGRP Configuration Commands

To enable the IGRP routing protocol on the Cisco Router, apply the following commands in router configuration mode.

R1# conf t
R1(config)# router igrp 1
R1(config-if)# network
R1(config-if)# network
R1(config-if)# end

  Final Word

What is Interior Gateway Routing Protocol IGRP? – In this article, we have briefly explained the Dynamic routing protocol, the Distance Vector IGRP protocol. It is important to note that Cisco no longer supports the IGRP protocol. Cisco recommends using the more advanced DV protocol EIGRP.

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