in the information such as a predefined field of a header the customer part 5 further comprises the selector 53 coupled to the detector 52 via the processor system 51 for selecting the service identifier s vlan in response to a detection of the destination property destination mac address thereto a table can be used in case of the destination property destination mac address being used before the service identifier s vlan can be retrieved from this table in case of the destination property destination mac address being used for the first time a default service identifier s vlan is to be generated preferably a first service identifier is linked to a first customer interface port 11 coupled to a first service interface port 21 and a second service identifier is linked to a second customer interface port 12 coupled to a second service interface port 22 in this case a selection of a service identifier s vlan corresponds with a selection of an interface port 11 12 and vice versa the network unit 1 may further comprise the memory 54 for storing a relationship between a source property in the information and a port 10 13 of the customer part 5 by storing a relationship between a source property such as a source address source mac address as defined in the information and a port of the customer part 5 such as a customer access port 10 or a customer interface port 11 13 the network unit 1 has got learning capabilities and can respond efficiently in case the destination 9 sends back information to the source 7 the source property.