The reliability of extra-stage interconnection networks is discussed. Three types of reliability are analyzed: terminal reliability, which is the probability that at least one fault-free path exists between a given input-output pair: network reliability, which is the probability that at least one fault-free path exists between every input-output pair; and broadcast reliability, which is the probability that at least one fault-free path exists between a given input and all outputs. A recursive expression for the broadcast reliability is obtained. Tight bounds are derived for the network reliability. The numerical results indicate that for practical networks (i.e. when network reliability is at least 0.5) the difference between the upper bound and the lower bound is no more than 2% of the lower bound. >