IGRP (Interior Gateway Routing Protocol) is a distance-vector routing protocol developed by Cisco to exchange routing data within an autonomous system. It's a proprietary protocol and considered obsolete, having been superseded by EIGRP (Enhanced Interior Gateway Routing Protocol).
Key Characteristics of IGRP:
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Distance Vector: IGRP is a distance-vector protocol, meaning that routers exchange their routing tables with their neighbors, advertising the distance (metric) to various networks.
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Cisco Proprietary: It's a Cisco-developed protocol and only works on Cisco routers.
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Metric: IGRP uses a composite metric based on bandwidth, delay, load, and reliability. However, by default, only bandwidth and delay are considered.
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Periodic Updates: IGRP sends routing updates every 90 seconds by default, which can consume bandwidth.
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Hop Count Limit: IGRP has a hop count limit of 255, limiting the size of the network it can support.
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Timers: IGRP utilizes various timers, including the update timer, invalid timer, and hold-down timer, to maintain routing information and prevent routing loops.
Why IGRP is Obsolete:
IGRP has been superseded by EIGRP (Enhanced Interior Gateway Routing Protocol), which offers several improvements, including:
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Faster Convergence: EIGRP converges faster than IGRP due to its use of Diffusing Update Algorithm (DUAL).
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Support for VLSM: EIGRP supports Variable Length Subnet Masks (VLSM), allowing for more efficient use of IP addresses.
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Bounded Updates: EIGRP sends only partial updates when a network change occurs, reducing bandwidth consumption.
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Support for Multiple Network Layer Protocols: EIGRP can support IP, IPX, and AppleTalk.
Example Scenario (Illustrative, but IGRP is rarely deployed now):
Imagine a small network with three Cisco routers (R1, R2, and R3). R1 is directly connected to a network A (192.168.1.0/24), R2 is directly connected to network B (192.168.2.0/24), and R3 is directly connected to network C (192.168.3.0/24). R1 is connected to R2, and R2 is connected to R3. If IGRP is configured, each router will exchange routing information. R1 will tell R2 about Network A. R2 will tell R1 about Network B and will tell R3 about networks A and B. R3 will tell R2 about Network C.
Summary:
IGRP is a Cisco proprietary distance-vector routing protocol that was used for routing within an autonomous system. While it served its purpose, its limitations led to the development of EIGRP, a more efficient and feature-rich routing protocol that has largely replaced it. IGRP is now considered obsolete.
