addresses of the outermost ip header are covered by ah authentication is used between the mobile terminal and the home server when the mobile terminal moves to a new network it sends a data packet which may be an empty data packet if there is no data to send that is processed using the ipsec sa bundle and sent to the home server once the home server properly authenticates the message including the outermost ip header and determines that it is coming from an address that differs from the current mobility binding it may update the mobility binding automatically updating the binding results in that all subsequent packets being destinated to the mobile terminal will be sent using the updated mobility binding i e the new address that the client is using thus no explicit mobility binding update signalling is required in this case the description of the invention above has been simplified for clarity of description the invention can be extended in several ways without changing the underlying idea some extensions are described in what follows the mobile ip concept of simultaneous bindings and associated traffic n casting from the home server to the mobile terminal can be used in this case packets sent towards the mobile terminal would be processed using several ipsec sas one for each.