Authentication@ Authorization@ and Accounting (AAA) servers@ such as RADIUS and DIAMETER@ are in use within the Internet today to provide authentication and authorization services for dial-up computers. Mobile IP for IPv4 requires strong authentication between the mobile node and its home agent. When the mobile node shares an AAA Security Association with its home AAA server@ however@ it is possible to use that AAA Security Association to create derived Mobility Security Associations between the mobile node and its home agent@ and again between the mobile node and the foreign agent currently offering connectivity to the mobile node. This document specifies extensions to Mobile IP registration messages that can be used to create Mobility Security Associations between the mobile node and its home agent@ and/or between the mobile node and a foreign agent.