Interior Gateway Routing Protocol (IGRP)

Interior Gateway Routing Protocol is a distance vector routing protocol developed by Cisco systems for routing multiple protocols across small and medium sized Cisco networks. It is proprietary which requires that you use Cisco routers. This contrasts with IP RIP and IPX RIP, which are designed for multi-vendor networks. IGRP will route IP, IPX, Decnet and AppleTalk which makes it very versatile for clients running many different protocols. It is somewhat more scalable than RIP since it supports a hop count of 100, only advertises every 90 seconds and uses a composite of five different metrics to select a best path destination. Note that since IGRP advertises less frequently, it uses less bandwidth than RIP but converges much slower since it is 90 seconds before IGRP routers are aware of network topology changes. IGRP does recognize assignment of different autonomous systems and automatically summarizes at network class boundaries. As well there is the option to load balance traffic across equal or unequal metric cost paths.

Characteristics

Distance Vector
Routes IP, IPX, Decnet, Appletalk
Routing Table Advertisements Every 90 Seconds
Metric: Bandwidth, Delay, Reliability, Load, MTU Size
Hop Count: 100
Fixed Length Subnet Masks
Summarization on Network Class Address
Load Balancing Across 6 Equal or Unequal Cost Paths ( IOS 11.0 )
Update Timer: 90 seconds
Invalid Timer: 270 seconds
Holddown Timer: 280 seconds
Metric Calculation = destination path minimum BW * delay (usec)
Split Horizon