Investigating the Filter Capacity of Linecouplers in KNX regarding network security

Building Automation Systems are used to enhance the energy consumption and to increase the comfort as well as the flexibility of buildings. In fieldbus networks and especially in KNX networks so called coupler units play a central role. They are used to connect the different network segments. To keep the broadcast traffic local they offer filter settings. This paper examines the filter capacity of different linecouplers under security aspects. To perform this a set of different telegrams was designed to test the selectivity according to the different header fields of the telegrams. It was found, that couplers only filter telegrams by checking their destination address and none of the other possible features. This means that these filters cannot be used in a security concept. As these filters can also be deactivated by only sending one reconfiguration telegram to the filter they do not allow to block advanced attackers.