Methods for operating virtual networks, data network system, computer program and computer program product

The invention relates to a method for operating virtual networks. The method comprises providing a first virtual network comprising a first set of network ports assigned to a first virtualization tag (T) and a second virtual network comprising a second set of network ports assigned to a second virtualization tag (T), the first and the second virtual network having compatible address ranges and being adapted to only pass data packets within them, providing a first network node having a source address (SA) in the first virtual network and being operationally connected to a first port (P) assigned to the first virtual network by means of the first virtualization tag (T), monitoring the first network node in order to detect a predetermined condition, and, on detection of the predetermined condition, reassigning the first port (P) to the second virtual network by means of assigning the second virtualization tag (T) to the first port (P), such that no data packet can be passed from the first network node (N) to a second network node (N) connected to a second port (P) assigned to the first virtual network by means of the first virtualization tag (T) directly and keeping of the source address (SA) for the first network node (N) in the second virtual network. The invention further relates to a further method for operation virtual networks, a data network system and a computer program product adapted to perform the inventive methods.