The main goals in the development of IGRP were to improve scalability and to overcome the maximum number of 15 network nodes specified by RIP that a target network may be away from before the network is considered to be inaccessible. The maximum number of routers between the starting point and destination ("hops") with IGRP is 255.
IGRP can use the available bandwidth, the delay occurring on the path, the line reliability and the line utilization to generate cost metrics. At IGRP, the metric is calculated using the formula
, for example on a T1 line at 1544kbps
is the delay time in 10 microsecond units, for example 20000 microsecond delay
By default, the cost metric of a route is formed from the bandwidth and the line delay, i. H. and and .