In this paper, we investigate the blocking performance of all-optical ring and mesh networks with Reconfigurable Optical Add-Drop Multiplexers (ROADMs) and tunable transponders. The ROADMs and transponders together determine the number and set of wavelengths that can be added/dropped leading to a wavelength termination constraint in addition to the well-known wavelength continuity constraint. We develop an analytical model for the blocking probability by accounting for both constraints and validate the model using simulation results. Specifically, a model for computing the blocking probability in a reconfigurable network of arbitrary topology wherein the number and tunability of the transponders are given parameters is presented. It is found that narrowly tunable transponders with a tuning range of about 4 in a 32-wavelength network provides nearly as good a performance as widely tunable transponders (tunable over the entire range of wavelengths), for a wide range of loads and number of transponders. Moreover, waveband assignment to narrowly tunable transponders is found to be a factor in some cases, and we present some results for two different assignment schemes.