The present disclosure envisages a computer implemented method, a corresponding computer implemented system and a computer program product that envisage inserting the mapping information—including source IP address and source port number—that maps the IP datagram back to its origin endpoint (i.e. the source computing node at which the IP datagram was originally created), into an IP-options field of the corresponding IP datagram. Additionally, the present disclosure envisages anticipating the default behaviour of the Network Address Translation (NAT) device (for instance, a gateway) characterized by replacement of the source IP address and the source port number (mapping information) stored in the IP header of the IP datagram with a translated IP address and translated port number, and facilitating trustful and non-repudiable verification of the source computing node as the creator of the IP datagram, on the destination computer network.