A technique for hiding topological information in a message that leaves a trusted network-domain is presented. The message pertains to a subscriber session and comprises a Fully Qualified Domain Name (FQDN) of a message originator. The originator is located in a first network domain, and the message is directed towards a destination in a second network domain. A method aspect comprises the steps of receiving the message, determining the FQDN comprised in the message and determining an identifier associated with the message. The identifier comprises at least one of a subscriber identifier, a session identifier and a destination identifier. Further, the method comprises applying a cryptographic operation on the FQDN and the identifier, or on information derived therefrom, to generate a cryptographic value. The message is then processed by substituting at least a portion of the FQDN with the cryptographic value prior to forwarding the message towards the second network domain.