AAA servers, in use within the Internet, provide authentication and authorization services for dial-up computers. These services are likely to be equally valuable for mobile nodes that use Mobile IP when the nodes attempt to connect to foreign domains with AAA servers. AAA servers use Network Access Identifier (NAI) to identify clients. A mobile node can identify itself by including the NAI in the Mobile IP registration request.
Because the NAI is typically used to identify the mobile node uniquely, the home address of the mobile node is not always necessary to provide that function. Thus, a mobile node can authenticate itself. Consequently, a mobile node can be authorized for connection to the foreign domain without even having a home address. To request that a home address be assigned, a message that contains the mobile node NAI extension can set the home address field to zero in the registration request.