A method for setting up expected communication behavior information in a communication system, the system comprising an external entity and a 5G system, 5GS, wherein the 5GS comprises a 5G core, 5GC, wherein the 5GC comprises a functional entity, a Unified Data Management, UDM, a Session Management Function, SMF, and a User Plane Function, UPF, wherein the expected communication behavior information comprises: addresses or User Equipments, UEs, that a UE is allowed to communicate to and an action that the 5GS has to take when a UE sends packets to an address or UE it is not allowed to communicate to, the method comprising the steps: performing, by the external entity, an Application Programming Interface, API, call via an API of the functional entity and setting up an expected communication behavior for a subscriber or set of subscribers, a Data Network Name, DNN, a 5G Virtual Network, VN, a slice or any combination thereof that the functional entity is allowed to manage; if the subscriber or set of subscribers is referred to via an IP address, IP address range, MAC address or MAC address range, mapping, at the functional entity, the address or address range to a subscriber or set of subscribers, and if the subscriber or set of subscribers is not indicated, this step is skipped; updating, at the UDM, by adding and storing, expected communication behavior information into one or more subscriber's information, wherein the subscriber information indicates none, one or a combination of: DNN, 5G VN Group, and/or Slice; sending a confirmation, from the functional entity to the external entity, that the setting up of an expected communication behavior for a subscriber or set of subscribers, a DNN, a 5G VN, a slice or any combination thereof, has been performed successfully; if the subscriber or set of subscribers have an active Protocol Data Unit, PDU, session or PDU sessions, wherein the SMF is subscribed in the UDM to changes of subscriber information of the subscriber or set of subscribers of the PDU session or PDU sessions, notifying (S5A), from the UDM to the subscribed SMF, of a change in the subscriber information, if the subscriber or set of subscribers have no active PDU sessions, whenever a SMF performs a PDU establishment procedure, the SMF retrieving (S5B) the subscriber information from the UDM, wherein the retrieved subscriber information contains the updated expected communication behavior information; for active PDU sessions, performing, from the SMF to the UPF, a N4 session modification procedure and updating the expected communication behavior in the UPF via N4 interface; for new PDU session establishments, signaling, via N4 interface, from the SMF to the UPF, the expected communication behavior information. performing, by the external entity, an Application Programming Interface, API, call via an API of the functional entity and setting up an expected communication behavior for a subscriber or set of subscribers, a Data Network Name, DNN, a 5G Virtual Network, VN, a slice or any combination thereof that the functional entity is allowed to manage; if the subscriber or set of subscribers is referred to via an IP address, IP address range, MAC address or MAC address range, mapping, at the functional entity, the address or address range to a subscriber or set of subscribers, and if the subscriber or set of subscribers is not indicated, this step is skipped; updating, at the UDM, by adding and storing, expected communication behavior information into one or more subscriber's information, wherein the subscriber information indicates none, one or a combination of: DNN, 5G VN Group, and/or Slice; sending a confirmation, from the functional entity to the external entity, that the setting up of an expected communication behavior for a subscriber or set of subscribers, a DNN, a 5G VN, a slice or any combination thereof, has been performed successfully; if the subscriber or set of subscribers have an active Protocol Data Unit, PDU, session or PDU sessions, wherein the SMF is subscribed in the UDM to changes of subscriber information of the subscriber or set of subscribers of the PDU session or PDU sessions, notifying (S5A), from the UDM to the subscribed SMF, of a change in the subscriber information, if the subscriber or set of subscribers have no active PDU sessions, whenever a SMF performs a PDU establishment procedure, the SMF retrieving (S5B) the subscriber information from the UDM, wherein the retrieved subscriber information contains the updated expected communication behavior information; for active PDU sessions, performing, from the SMF to the UPF, a N4 session modification procedure and updating the expected communication behavior in the UPF via N4 interface; for new PDU session establishments, signaling, via N4 interface, from the SMF to the UPF, the expected communication behavior information.