HTTP/1.1 200 OK Date: Tue, 09 Apr 2002 06:38:52 GMT Server: Apache/1.3.20 (Unix) Last-Modified: Tue, 25 Mar 1997 09:07:00 GMT ETag: "304d70-8023-333795b4" Accept-Ranges: bytes Content-Length: 32803 Connection: close Content-Type: text/plain PPP Extensions Working Group J. Solomon, Motorola Internet Draft S. Glass, FTP Software expires September 24, 1997 March 24, 1997 Mobile IPv4 Configuration Option for PPP IPCP Status of this Memo This document is a submission to the PPPEXT working group of the IETF, having already reached consensus within the MOBILEIP working group. Questions can be directed to the respective mailing lists: ietf-ppp@merit.edu and mobile-ip@smallworks.com. This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as ``work in progress.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Distribution of this memo is unlimited. Abstract 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 point- to-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. Solomon & Glass expires September 24, 1997 [Page 1] Internet Draft Mobile IP Option for PPP March 24, 1997 Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . 2 1.2. Problem Statement . . . . . . . . . . . . . . . . . . . 3 1.3. Requirements . . . . . . . . . . . . . . . . . . . . . . 5 2. Mobile IPv4 Configuration Option . . . . . . . . . . . . . . . 6 3. Additional Requirements . . . . . . . . . . . . . . . . . . . 9 3.1. Other IPCP Options . . . . . . . . . . . . . . . . . . . 9 3.2. Move Detection . . . . . . . . . . . . . . . . . . . . . 9 4. Supported Scenarios . . . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 13 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 8. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 15 1. Introduction Mobile IP [RFC 2002] defines protocols and procedures by which packets can be routed to a mobile node, regardless of its current point-of-attachment to the Internet, and without changing its IP address. Mobile IP is designed to run over any type of media and any type of data link-layer. However, the interaction between Mobile IP and PPP is currently underspecified and generally results in an inappropriate application of Mobile IP when mobile nodes connect to the Internet via PPP. This document defines proper interaction between a mobile node [RFC 2002] and a dialup server through which the mobile node connects to the Internet using PPP. This requires the definition of a new option for IPCP [RFC 1332], named the "Mobile IPv4 Configuration Option", which is defined in this document. The mobile node and the dialup server use this option to negotiate the appropriate use of Mobile IP over the PPP link. 1.1. Terminology This document uses the following terms as defined in [RFC 2002]: Mobile Node A host or router that changes its point of attachment from one network or subnetwork to another. A mobile node may change its location without changing its IP address; it may continue to communicate with other Internet nodes at any location using its (constant) IP address, assuming link-layer connectivity to a point of attachment is available. Solomon & Glass expires September 24, 1997 [Page 2] Internet Draft Mobile IP Option for PPP March 24, 1997 Home Agent A router on a mobile node's home network which tunnels datagrams for delivery to the mobile node when it is away from home, and maintains current location information for the mobile node. Foreign Agent A router on a mobile node's visited network which provides routing services to the mobile node while registered. The foreign agent detunnels and delivers datagrams to the mobile node that were tunneled by the mobile node's home agent. For datagrams sent by a mobile node, the foreign agent may serve as a default router for registered mobile nodes. Dialup Server The PPP peer of a mobile node. A dialup server might support home agent functionality, foreign agent functionality, both, or neither. 1.2. Problem Statement In Mobile IP, packets sent to a mobile node's home address are routed first to the mobile node's home agent, a router on the mobile node's home link which intercepts packets sent to the home address. The home agent then tunnels such packets to the mobile node's care-of address, where the packets are extracted from the tunnel and delivered to the mobile node. There are two types of care-of addresses: Co-located Care-of Address An address temporarily assigned to a mobile node itself. In this case, the mobile node is the exit-point of the tunnel and decapsulates packets encapsulated for delivery by its home agent. Foreign Agent Care-of Address An address of a foreign agent that has at least one interface on a mobile node's visited link. In this case, the foreign agent decapsulates packets that have been tunneled by the home agent and delivers them to the mobile node over the visited link. Solomon & Glass expires September 24, 1997 [Page 3] Internet Draft Mobile IP Option for PPP March 24, 1997 In Appendix B, Mobile IP [RFC 2002] currently specifies only the following with respect to PPP: "The Point-to-Point-Protocol (PPP) [RFC 1661] and its Internet Protocol Control Protocol (IPCP) [RFC 1332], negotiates the use of IP addresses. "The mobile node SHOULD first attempt to specify its home address, so that if the mobile node is attaching to its home network, the unrouted link will function correctly. When the home address is not accepted by the peer, but a transient IP address is dynamically assigned to the mobile node, and the mobile node is capable of supporting a co-located care-of address, the mobile node MAY register that address as a co-located care-of address. When the peer specifies its own IP address, that address MUST NOT be assumed to be a foreign agent care-of address or the IP address of a home agent." Inspection of this text reveals that there is currently no way for the mobile node to use a foreign agent care-of address, without first being assigned a unique IP address, even if the dialup server also supports foreign agent functionality. The reason for this can be seen by walking through the IPCP negotiation: 1. A mobile node calls a dialup server and proposes its home address in IPCP's "IP Address" option. 2. The dialup server has no way of knowing whether this is: (a) a mobile node proposing its home address; or (b) a conventional node proposing a non-routable address. In this case, the dialup server must (conservatively) Nak the IP address option. 3. The mobile node, in turn, has no way of knowing whether its home address was Nak'ed because the peer is a foreign agent being conservative, or because the peer does not implement Mobile IP at all. Therefore, the mobile node must (conservatively) assume that the peer does not implement Mobile IP and continue the negotiation of an IP address in IPCP, after which point the mobile node can use the assigned address as a co-located care-of address. Here we observe that, even if the dialup server is a foreign agent and sends an Agent Advertisement to the mobile node after IPCP completes, the mobile node will still have negotiated a routable address in step 3 which it is likely already using as a co-located care-of address. This defeats the purpose of foreign agent care-of addresses, which are designed to be shared by multiple mobile nodes and to eliminate the need to assign a unique address to each mobile node. Solomon & Glass expires September 24, 1997 [Page 4] Internet Draft Mobile IP Option for PPP March 24, 1997 1.3. Requirements The purpose of this document is to specify the behavior of both ends of the PPP link when one or more of the PPP peers supports Mobile IP. Specifically, the design of the option and protocol defined in this document is based upon the following requirements: 1. The option and protocol described in this document must be backwards compatible with conventional nodes and dialup servers which do not implement this option nor any Mobile IP functionality. 2. The option and protocol described in this document must accommodate a variety of scenarios, minimally those identified in Section 4. 3. A unique address must not be assigned to a mobile node unless absolutely necessary. Specifically, no such address is assigned to a mobile node that connects via PPP to its home link or a mobile node that connects via PPP to a foreign agent (and uses that foreign agent's care-of address). Solomon & Glass expires September 24, 1997 [Page 5] Internet Draft Mobile IP Option for PPP March 24, 1997 2. Mobile IPv4 Configuration Option The Mobile IPv4 Configuration Option for IPCP is defined as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length |D| reserved1 |C|H| reserved2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Mobile Node's Home Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Assigned Co-Located Care-Of Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 137 (Mobile IPv4 Configuration Option) Length 12 (The length of this entire extension in bytes) D 1, if the Mobile Node wants a Dynamically assigned, co-located care-of address, 0 otherwise. reserved1 sent as 0, ignored on reception C 1, if the dialup server Cannot fulfill the mobile node's request to be dynamically assigned a co-located care-of address, 0 otherwise. H 1, if the PPP interface of the dialup server is a neighbor of the mobile node's home address on the home link, 0 otherwise. reserved2 sent as 0, ignored on reception Mobile Node's Home Address The IP home address of the mobile node sending the Mobile IPv4 Configuration Option. Assigned Co-Located Care-of Address A place-holder for the dynamically assigned co-located care-of address. Ignored if the 'D' bit is 0. The option works as follows. A mobile node includes the Mobile IPv4 Configuration Option in a Configure-Request of IPCP. A mobile node MUST NOT include an IP Address Option (nor the deprecated IP- Addresses Option) along with the Mobile IPv4 Configuration Option but MAY include other options that do not involve negotiation of an IP address (see section 3.1). Solomon & Glass expires September 24, 1997 [Page 6] Internet Draft Mobile IP Option for PPP March 24, 1997 The mobile node MUST set the 'D' bit to 1 if it wants to be assigned a co-located care-of address, otherwise it MUST set the 'D' bit to 0. The mobile node SHOULD set all other fields and bits to 0, except for the "Mobile Node's Home Address" field in which it MUST place its IP home address. The response generated at the other end of the PPP link depends upon the identity and the capabilities of the PPP peer (for simplicity, we call this peer a "dialup server"). Several cases are described as follows, which assume that the dialup server has received a Configure-Request from the mobile node containing a Mobile IPv4 Configuration Option: 1. If the Mobile IPv4 Configuration Option is not recognizable or is not acceptable for negotiation (as configured by a network administrator), then the dialup server MUST respond by sending a Configure-Reject, as described in [RFC 1661]. A mobile node that receives such a Configure-Reject MAY proceed with IPCP negotiation using the IP Address Option [RFC 1332] instead of the Mobile IPv4 Configuration Option. The address so negotiated MAY be used by the mobile node as a co-located care-of address. If, instead, the Mobile IPv4 Configuration Option is recognizable and is acceptable for negotiation, then the dialup server MUST respond with either a Configure-Ack or a Configure-Nak, depending upon the acceptability of the specific values contained within the Mobile IPv4 Configuration Option. Each such case is described below where, due to the recognizability of the Mobile IPv4 Configuration Option, we assume that the dialup server is either a home agent, a foreign agent, or both. 2. If the dialup server is a bridge with one interface on the mobile node's home network or if the dialup server is a router whose address on its PPP interface is a neighbor to the mobile node's home address (i.e., the mobile node is connecting to its home link), then the dialup server sends a Configure-Nak in which it sets the 'H' bit to 1 and leaves all other fields unmodified. A mobile node receiving this Configure-Nak MUST respond by sending a new Configure-Request (containing the Mobile IPv4 Configuration Option) with D=0, C=0, H=1, Mobile Node's Home Address field set to the mobile node's IP home address, and the Assigned Co-Located Care-of Address field set to 0. The dialup server will subsequently send a Configure-Ack in response to this new Configure-Request and IPCP will complete. The mobile node is not required to wait for an Agent Advertisement before de-registering with its home agent. Solomon & Glass expires September 24, 1997 [Page 7] Internet Draft Mobile IP Option for PPP March 24, 1997 All the remaining cases assume that the dialup server is a foreign agent to the mobile node and specifically not connected to the mobile node's home link (as determined by the Mobile Node's Home Address field). 3. If the mobile node set the 'D' bit to 1, if the Assigned Co- Located Care-of Address is set to a value never previously assigned to this mobile node (e.g., 0.0.0.0), and if the foreign agent is capable of assigning an address, then the foreign agent MUST respond with a Configure-Nak in which a newly assigned co- located care-of address is placed in the Assigned Co-Located Care-of Address field and all other fields are left unmodified. A mobile node receiving such a Configure-Nak MUST respond by sending a new Configure-Request containing a Mobile IPv4 Configuration Option copied without modification from this received Configure- Nak. The foreign agent MUST respond to this new Configure-Request with a Configure-Ack. As specified in [RFC 1661] and [RFC 1332], a mobile node MUST receive such a Configure-Ack before it can consider IPCP to be completed and therefore that it may use the assigned address as a co-located care-of address. In addition, the mobile node MUST (!) wait for an Agent Advertisement before registering this co-located care-of address. This is because the foreign agent might set the 'R' Bit in its Agent Advertisements (see [RFC 2002]) which forces the mobile node to register via the foreign agent, even when using a co-located care-of address. Accordingly, the foreign agent MUST send an Agent Advertisement over a PPP link immediately after IPCP for that link enters the Opened state. 4. If the mobile node set the 'D' bit to 1, and if the Assigned Co- Located Care-of Address is set to a value previously assigned to this mobile node by this foreign agent (i.e., as assigned in case #3 above), then the foreign agent MUST respond with a Configure- Ack and IPCP completes. The mobile node MUST (!) wait for an Agent Advertisement from the foreign agent before registering. This is because the foreign agent might set the 'R' Bit in its Agent Advertisements (see RFC 2002) which forces the mobile node to register via the foreign agent, even when using a co-located care-of address. Accordingly, the foreign agent MUST send an Agent Advertisement over a PPP link immediately after IPCP for that link enters the Opened state. Solomon & Glass expires September 24, 1997 [Page 8] Internet Draft Mobile IP Option for PPP March 24, 1997 5. If the mobile node set the 'D' bit to 1, and if the foreign agent is *not* capable of assigning an address, then the foreign agent MUST respond with a Configure-Nak in which the 'C' bit is set to 1 and all other fields are left unmodified. The mobile node must now either give up and try to find a dialup server that can assign an address, or proceed to use a foreign agent care-of address. In the latter case, the mobile node sends a new Configure-Request containing the Mobile IPv4 Configuration Option with the 'D' bit set to 0, as described in item #6 below. 6. If the mobile node set the 'D' bit to 0, then the foreign agent MUST return the option unmodified in a Configure-Ack and IPCP completes. The mobile node MUST wait for an Agent Advertisement from the foreign agent before registering. Accordingly, the foreign agent MUST send an Agent Advertisement over a PPP link immediately after IPCP for that link enters the Opened state. The design and semantics of the Mobile IPv4 Configuration Option are therefore optimized for the case of a mobile node making use of a foreign agent's care-of address. The negotiation takes only one round-trip in this case. 3. Additional Requirements 3.1. Other IPCP Options Although a mobile node MUST NOT include an IP Address Option (nor the deprecated IP-Addresses Option) in any Configure-Request that contains a Mobile IPv4 Configuration Option, the mobile node MAY include an IP-Compression-Protocol Option or any other option that does not involve the negotiation of an IP address. If a mobile node and a foreign agent or home agent agree in IPCP to use Van Jacobson Header Compression [RFC 1144], then the mobile node MUST NOT set the 'V' bit in its ensuing, Mobile IP Registration Request [RFC 2002]. 3.2. Move Detection Mobile nodes that connect via PPP MUST correctly implement PPP's IPCP, since movement by the mobile node will likely change its PPP peer. Specifically, mobile nodes MUST be prepared to re-negotiate IPCP at any time, including, the re-negotiation of the Mobile IPv4 Configuration Option described in this document. Also note that certain wireless links can employ handoff and proxying mechanisms that would not necessarily require bringing down a PPP link but would indeed require a mobile node to register with a new foreign agent. Therefore, mobile nodes which connect to an agent via PPP MUST employ their move detection algorithms (see section 2.4.2 in Solomon & Glass expires September 24, 1997 [Page 9] Internet Draft Mobile IP Option for PPP March 24, 1997 [RFC 2002]) and register whenever they detect a change in connectivity. Specifically, a mobile node that fails to receive an Agent Advertisement within the Lifetime advertised by its current foreign agent, MUST assume that it has lost contact with that foreign agent (see Section 2.4.2.1, [RFC 2002]). If, in the mean time, the mobile node has received Agent Advertisements from another foreign agent, the mobile node SHOULD immediately register with that foreign agent upon timing out with its current foreign agent. Likewise, a mobile node that implements move detection based upon the Prefix-Length Extension MUST compare the prefix of any advertising agents with that of its current foreign agent (see Section 2.4.2.2, [RFC 2002]). If such a mobile node receives an Agent Advertisement from a foreign agent specifying a different prefix than that of its current foreign agent, then the mobile node that employs this method of move detection MUST register with that new foreign agent. A mobile node MAY treat PPP link-establishment as a sufficient reason to proceed with a new Mobile IP registration. Section 2 defines the circumstances under which mobile nodes MUST wait for an Agent Advertisement before registering. Accordingly, foreign agents and home agents MUST send an Agent Advertisement over a PPP link immediately after IPCP for that link enters the Opened state. 4. Supported Scenarios The Mobile IPv4 Configuration Option is designed to accommodate the following scenarios. This section also helps to illustrate the use of the option and the protocol specified above. In the scenarios which follow, the direction of message flow is indicated along with the type of IPCP message and the contents of the appropriate option. "MN" refers to the mobile node and "dialup" refers to the PPP peer to which the mobile node connects. For sake of brevity, the Type, Length, Reserved, and Mobile Node's Home Address fields have been omitted from the Mobile IPv4 Configuration Option below because these fields are always set to their obvious values. Finally, the Assigned Co-Located Care-Of Address field is designated by "IPcol-coa". Solomon & Glass expires September 24, 1997 [Page 10] Internet Draft Mobile IP Option for PPP March 24, 1997 A. A mobile node wants to use a co-located care-of address and the dialup server is a foreign agent that is capable of assigning such an address: [ From -> To ] PPP Message Type Mobile IPv4 Configuration Option ============== ================= ================================ [MN -> dialup] Configure-Request {D=1,C=0,H=0,IPcol-coa=0.0.0.0} [dialup -> MN] Configure-Nak {D=1,C=0,H=0,IPcol-coa=new-coa} [MN -> dialup] Configure-Request {D=1,C=0,H=0,IPcol-coa=new-coa} [dialup -> MN] Configure-Ack {D=1,C=0,H=0,IPcol-coa=new-coa} - Mobile node waits to receive an Agent Advertisement. - If (Advertisement has R-bit set) then Mobile node registers with co-located care-of address via the foreign agent; else Mobile node registers with co-located care-of address directly with its home agent. B. A mobile node wants to use a co-located care-of address and the dialup server is a foreign agent. The foreign agent cannot assign a co-located care-of address (e.g., it has no pool of addresses from which to allocate for the purposes of assignment): [ From -> To ] PPP Message Type Mobile IPv4 Configuration Option ============== ================= ================================ [MN -> dialup] Configure-Request {D=1,C=0,H=0,IPcol-coa=0.0.0.0} [dialup -> MN] Configure-Nak {D=1,C=1,H=0,IPcol-coa=0.0.0.0} The mobile node has two options: either proceed to use this foreign agent's care-of address or disconnect and try to find a different dialup server which can fulfill the request for a co- located care-of address. In the former case, IPCP continues as follows: [ From -> To ] PPP Message Type Mobile IPv4 Configuration Option ============== ================= ================================ [MN -> dialup] Configure-Request {D=0,C=0,H=0,IPcol-coa=0.0.0.0} [dialup -> MN] Configure-Ack {D=0,C=0,H=0,IPcol-coa=0.0.0.0} - IPCP completes. - Mobile node waits to receive an Agent Advertisement. - Mobile node registers with its home agent via the foreign agent. Solomon & Glass expires September 24, 1997 [Page 11] Internet Draft Mobile IP Option for PPP March 24, 1997 C. A mobile node wants to use a foreign agent care-of address and the dialup server is a foreign agent which finds this state of affairs satisfactory: [ From -> To ] PPP Message Type Mobile IPv4 Configuration Option ============== ================= ================================ [MN -> dialup] Configure-Request {D=0,C=0,H=0,IPcol-coa=0.0.0.0} [dialup -> MN] Configure-Ack {D=0,C=0,H=0,IPcol-coa=0.0.0.0} - IPCP completes. - Mobile node waits to receive an Agent Advertisement. - Mobile node registers with its home agent via the foreign agent. D. A mobile node connects to a dialup server which is connected to the mobile node's home link (for this scenario, it does not matter whether the mobile node wishes to use a co-located care-of address or a foreign agent care-of address). The dialup server informs the mobile node that it is connected to its home link as follows (the notation "D=x" implies a "don't care" condition): [ From -> To ] PPP Message Type Mobile IPv4 Configuration Option ============== ================= ================================ [MN -> dialup] Configure-Request {D=x,C=0,H=0,IPcol-coa=0.0.0.0} [dialup -> MN] Configure-Nak {D=x,C=0,H=1,IPcol-coa=0.0.0.0} [MN -> dialup] Configure-Request {D=0,C=0,H=1,IPcol-coa=0.0.0.0} [dialup -> MN] Configure-Ack {D=0,C=0,H=1,IPcol-coa=0.0.0.0} - IPCP completes. - Mobile node de-registers with its home agent. Solomon & Glass expires September 24, 1997 [Page 12] Internet Draft Mobile IP Option for PPP March 24, 1997 E. A mobile node wants to use either type of care-of address and the dialup server does not implement the Mobile IPv4 Configuration Option. The server rejects the option as follows (the notation "D=x" implies a "don't care" condition): [ From -> To ] PPP Message Type Mobile IPv4 Configuration Option ============== ================= ================================ [MN -> dialup] Configure-Request {D=x,C=0,H=0,IPcol-coa=0.0.0.0} [dialup -> MN] Configure-Reject {D=x,C=0,H=0,IPcol-coa=0.0.0.0} At this point, the mobile node can use the IP Address Option [RFC 1332] to negotiate an address which it can subsequently use as a co-located care-of address: [ From -> To ] PPP Message Type ***IP Address Option*** ============== ================= =============================== [MN -> dialup] Configure-Request {IPaddress = 0.0.0.0} [dialup -> MN] Configure-Nak {IPaddress = assigned-address} [MN -> dialup] Configure-Request {IPaddress = assigned-address} [dialup -> MN] Configure-Ack {IPaddress = assigned-address} - IPCP completes. - Mobile node registers "IPaddress" as a co-located care-of address with its home agent. 5. Security Considerations This document introduces no known security threats over and above those facing any node on the Internet that either connects via PPP or implements Mobile IP or both. Specifically, service providers should use cryptographically strong authentication (e.g., CHAP [RFC 1994]) to prevent theft-of-service. Additionally, users requiring confidentiality should use PPP link encryption [RFC 1968], IP-layer encryption [RFC 1827], or application-layer encryption, depending upon their individual requirements. Finally, Mobile IP authentication [RFC 2002] protects against trivial denial-of-service attacks that could otherwise be waged against a mobile node and its home agent. Solomon & Glass expires September 24, 1997 [Page 13] Internet Draft Mobile IP Option for PPP March 24, 1997 6. References [RFC 1144] Jacobson, V., "Compressing TCP/IP Headers for Low-Speed Serial Links", RFC 1144, January 1990. [RFC 1332] McGregor, G., "The PPP Internet Protocol Control Protocol (IPCP)," RFC 1332, May 1992. [RFC 1661] Simpson, W., Editor, "The Point-to-Point Protocol (PPP) for the Transmission of Multi-protocol Datagrams over Point-to- Point Links," RFC 1661, July 1994. [RFC 1827] Atkinson, R., "IP Encapsulating Security Payload (ESP)", RFC 1827, August 1995. [RFC 1994] Simpson, W., "PPP Challenge Handshake Authentication Protocol (CHAP)", RFC 1994, August 1996. [RFC 1968] Meyer, G., "The PPP Encryption Control Protocol (ECP)", RFC 1968, June 1996. [RFC 2002] Perkins, C., Editor, "IP Mobility Support", RFC 2002, October 1996. 7. Acknowledgments The design of this protocol and option were inspired by an earlier submission by B. Patel and C. Perkins, then of IBM, in draft-patel- mobileip-pppext-00.txt, which has since expired. Tim Wilson and Chris Stanaway of Motorola contributed significantly to the design of this configuration option and protocol specification. Also, some of William Simpson's text was copied verbatim from [RFC 1661] in order to ensure consistency of terminology and specification. The same goes for Charlie Perkins' text, including definitions, from [RFC 2002]. Solomon & Glass expires September 24, 1997 [Page 14] Internet Draft Mobile IP Option for PPP March 24, 1997 8. Authors' Addresses Questions about this memo can be directed to: Jim Solomon Motorola, Inc. 1301 E. Algonquin Rd. - Rm 2240 Schaumburg, IL 60196 Voice: +1-847-576-2753 Fax: +1-847-576-3240 E-Mail: solomon@comm.mot.com Steven Glass FTP Software, Inc. 2 High Street North Andover, MA 01845 Voice: +1-508-685-4000 Fax: +1-508-684-6105 E-mail: glass@ftp.com Solomon & Glass expires September 24, 1997 [Page 15]