Method and arrangement for implementing ipsec policy management using filter code

A data processing system implements a security protocol based on processing data in packets. The data processing system comprises processing packets for storing filter code and processing data packets according to stored filter code, and a policy managing function for generating filter code and communicating generated filter code for packet processing. The packet processing function is arranged to examine, whether the stored filter code is applicable for processing a certain packet. If the stored filter code is not applicable for the processing of a packet, the packet is communicated to the policy managing function, which generates filter code applicable for the processing of the packet and communicates the generated filter code for packet processing.