AbstractWe envision a large‐scale multiclass optical network in which lightpaths are dynamically set up and terminated between source and destination nodes and these lightpaths traverse through a number of interconnected WDM networks in different administrative domains. In this envisioned multiclass network, calls are classified by the number of wavelengths demanded per call and the statistics of call holding times (or service subscription periods). We present an approximation method for the performance analysis of such a large‐scale multiclass optical WDM network. We model the large‐scale optical network as a two‐level hierarchical multiclass loss network; the lower level of hierarchy consists of individual optical WDM networks (network segments). Each of these network segments is abstracted to a logical node at the higher level of hierarchy, and these logical nodes are connected to each other through logical links. We also assume that the call processing mechanism in this large‐scale optical network resorts to hierarchical routing. The algorithms presented in this paper computeper‐class end‐to‐end approximate blocking probabilities. Our experiments show that the simulation results match closely with the results of the proposed analytical approximation methods, thus validating the proposed methodology. Copyright © 2010 John Wiley & Sons, Ltd.