1. A network node for a communication network having a first subnetwork using a spanning tree protocol and a second subnetwork connected to the first subnetwork, the second subnetwork using a second protocol differing from the spanning tree protocol of the first subnetwork: the network node being configured as an element of the second subnetwork and configured for communication within the second subnetwork; and wherein the network node is configured by a spanning tree functionality as a spanning tree master node to check and control the second subnetwork such that the second subnetwork is handled or is able to be handled by the spanning tree protocol of the first subnetwork as a virtual network node such that the second subnetwork is identifiable as a single node by the first subnetwork.