Mobile IP [RFC 2002] defines media-independent procedures by which a Mobile Node can maintain existing transport and application-layer connections despite changing its point-of-attachment to the Internet and without changing its IP address. PPP [RFC 1661] provides a standard method for transporting multi-protocol packets over pointto- point links. As currently specified@ Mobile IP Foreign Agents which support Mobile Node connections via PPP can do so only by first assigning unique addresses to those Mobile Nodes@ defeating one of the primary advantages of Foreign Agents. This documents corrects this problem by defining the Mobile-IPv4 Configuration Option to the Internet Protocol Control Protocol (IPCP) [RFC 1332]. Using this option@ two peers can communicate their support for Mobile IP during the IPCP phase of PPP. Familiarity with Mobile IP [RFC 2002]@ IPCP [RFC 1332]@ and PPP [RFC 1661] is assumed.