Clos Rearrangeable Switching Networks (RSN\´s) are examined with regard to properties of imprimitivity. It is shown that a certain version of RSN\´s built by 2 × 2 matrices in all stages except in the center stage have properties that imply a routing procedure for base 2
tRSN\´s (

is any positive integer) based on the looping procedure. The routing procedure gives, in turn, control data applicable to base 2, base 4, ..., base 2
tRSN\´s. Necessary computing time increases only linearly with the number of inputs if the maximum degree of parallelism is utilized. The obtained results can be applied to networks with an arbitrary base

by omitting unnecessary parts of a suitable base 2
tnetwork.