the care of address after successful authentication and authorization the mobile station ms sends a so called dhcp discovery message a dialog is now undertaken with an ip address allocation between mobile terminal me dhcp proxy and dhcp server after the ip address allocation there is an mip registration with the home agent being informed about the current location of the mobile station for its registration the pmip client sends representing the mobile station sends a registration request to the home agent ha containing the current care of address the home agent accepts the care of address and replies with a registration reply since in principle each computer can send a registration request to a home agent it would be a simple matter to fool a home agent into believing a computer or a mobile terminal had moved to another network to prevent this both the mobile terminal and also the home agent have a common secret key pmip key the pmip key or mobility key which differs from the authentication key aaa key the registration request is transmitted by a pmip client within the access network via a foreign agent fa to the home agent ha the home agent ha can be allocated by the associated authentication server aaa server the key for.