The Interior GatewayRouting Protocol (IGRP) is a modified distance vector protocol, the Interior Gateway Protocol (IGP). The IGRP protocol works with Distance Vector algorithm, it was developed by Cisco and is distinguished from the Routing Information Protocol (RIP) by a metric with which the optimal route is calculated.
This metric takes into account the transmission time with the delay times in the routers and on the link, the bandwidth of the transmission route considering the lowest bandwidth of sub-routes, the line utilization and the reliability which is determined by the error rate of a link.
The IGRP protocol uses these parameters to calculate the optimal route, which also takes into account the quality of the path. IGRP regularly sends routing tables and their updates to all neighboring routers at short intervals. These then update their own routing tables.
The IGRP protocol is characterized by a high stability, it has a low overhead, considers load distributions as well as the quality and the line utilization of the paths. Thereby, IGRP can include the different services and their service characteristics with its own parameters in the routing tables. To ensure the stability of the path, IGRP has some functions to avoid wrong routes and block deleted routes for a certain time. In addition, in case of error or route change, the routing table updates can be sent immediately.