The complexity (number of entities, interactions between entities, and resulting emergent dynamic behavior) of large communication environments which contain hundreds of nodes and links make simulation an important tool for the study of such systems. Given the difficulties associated with complete analytical treatment of complex dynamical systems, it is often the only practical tool that is available. This paper presents an example of a flexible, modular, object-oriented toolbox designed to support modeling and experimental analysis of a large family of heuristic knowledge representation and decision functions for adaptive self-managing communication networks with particular emphasis on routing strategies. It discusses in detail, the design, implementation, and validation of the toolbox using the discrete event simulation paradigm. It addresses several major practical design challenges presented by potentially large computational time and memory requirements of simulation of large communication networks and describes novel solutions adapted from the simulation and performance modeling and analysis literature to meet such challenges. It also examines some issues that arise in the validation of the resulting object-oriented simulation and modeling toolbox.