In this master thesis some new helpful features will be added to the Spanning Tree Simulator. This simulator was created by Andreas Sebastian Janke in his bachelor thesis [Jan10b] in 2010. It is possible to visualize networks which are defined in a configuration file. Each of them is a XML representation of a network consisting of switches and hosts. After loading such a file into the program it is possible to run the Spanning Tree Algorithm IEEE 802.1D. In contrast to the previous version only the switches are implemented as threads. When the algorithm is finished a spanning tree is built. This means, that messages cannot run into loops anymore. This is important because loops can cause a total breakdown of the communication in a network, if the running routing protocols cannot handle loops.