There are provided measures for supporting an authentication to an external packet data network over an untrusted access network, said measures exemplarily comprising authenticating a user equipment to a communication network providing connectivity for the user equipment across an unsecured access network in response to a first authentication request, wherein the authentication request is an authentication request of a key information exchange mechanism and includes authentication data, receiving a second authentication request for authenticating the user equipment towards a packet data network external to the communications network. The measures may further comprise creating a binding update message including the authentication data and identity information of the user received from the user equipment.