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Network Working Group                                         J. SolomonRequest for Comments: 2290                                      MotorolaUpdates:2002                                                   S. GlassCategory: Standards Track                                   FTP Software                                                           February 1998Mobile-IPv4 Configuration Option for PPP IPCPStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (1998).  All Rights Reserved.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.Table of Contents1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . .21.1. Specification Language . . . . . . . . . . . . . . . . .21.2. Terminology  . . . . . . . . . . . . . . . . . . . . . .21.3. Problem Statement  . . . . . . . . . . . . . . . . . . .31.4. Requirements . . . . . . . . . . . . . . . . . . . . . .52. Mobile-IPv4 Configuration Option . . . . . . . . . . . . . . .62.1. Option Format  . . . . . . . . . . . . . . . . . . . . .62.2. Overview . . . . . . . . . . . . . . . . . . . . . . . .7Solomon & Glass             Standards Track                     [Page 1]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 19982.3. High-Level Requirements for Non-Mobile-Nodes . . . . . .72.4. High-Level Requirements for Mobile Nodes . . . . . . . .82.5. Detailed Description . . . . . . . . . . . . . . . . . .82.6. Example Scenarios  . . . . . . . . . . . . . . . . . . .123. Additional Requirements  . . . . . . . . . . . . . . . . . . .143.1. Other IPCP Options . . . . . . . . . . . . . . . . . . .143.2. Move Detection . . . . . . . . . . . . . . . . . . . . .144. Security Considerations  . . . . . . . . . . . . . . . . . . .155. References . . . . . . . . . . . . . . . . . . . . . . . . . .156. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .167. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .168. Full Copyright Statement . . . . . . . . . . . . . . . . . . .171. 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 peer 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 peer use this   option to negotiate the appropriate use of Mobile IP over the PPP   link.   The Mobile-IPv4 option defined in this document is intended to work   in conjunction with the existing IP-Address option [RFC 1332].1.1. Specification Language   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described inRFC 2119.1.2. Terminology   This document uses the following terms as defined in [RFC 2002]:Solomon & Glass             Standards Track                     [Page 2]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 1998      Mobile Node         A host or router that changes its point-of-attachment from one         link 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 (permanent)         home, IP address, assuming link-layer connectivity is available         at its current location.      Home Agent         A router with at least one interface on a mobile node's home         link.  A home agent intercepts packets destined to a mobile         node's home address and tunnels them to the mobile node's         care-of address when the mobile node is connected to a foreign         link.  A mobile node informs its home agent of its current         care-of address through an authenticated registration protocol         defined by Mobile IP.      Foreign Agent         A router with at least one interface on a mobile node's         (current) foreign link.  When a mobile node uses a foreign         agent's care-of address, the foreign agent detunnels and         delivers packets to the mobile node that were tunneled by the         mobile node's home agent.  A foreign agent might also serve as         a default router for packets sent by a registered mobile node.      Peer         The PPP peer of a mobile node.  The mobile node's peer might         support home agent functionality, foreign agent functionality,         both, or neither.1.3. 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:Solomon & Glass             Standards Track                     [Page 3]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 1998   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.      A Co-located Care-of Address may be used by exactly one mobile      node at any point in time.   Foreign Agent Care-of Address      An address of a foreign agent that has at least one interface on a      mobile node's visited, foreign 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.      A Foreign Agent Care-of Address may be used simultaneously by many      mobile nodes at any point in time.   InAppendix 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 [sic] 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 [link], 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 peer also supports   foreign agent functionality.  The reason for this can be seen by   walking through the IPCP negotiation:    1. A mobile node connects to a peer via PPP and proposes its home       address in an IPCP Configure-Request containing the IP-Address       option.  In this scenario, we assume that the mobile node is       connecting to some foreign link.Solomon & Glass             Standards Track                     [Page 4]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 1998    2. The peer has no way of knowing whether this Configure-Request was       received from: (a) a mobile node proposing its home address; or       (b) a conventional node proposing some topologically non-routable       address.  In this case, the peer must (conservatively) send a       Configure-Nak of the IP-Address option supplying a topologically       appropriate address for use by the node at the other end of the       PPP link.    3. The mobile node, in turn, has no way of knowing whether this       Configure-Nak was received 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 mobile node's peer is a foreign   agent and sends an Agent Advertisement to the mobile node after IPCP   reaches the Opened state, 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.1.4. 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 their potential       peers 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 provided in       the examples ofSection 2.6.    3. The option and protocol described in this document must not       duplicate any functionality already defined in other IPCP       options; specifically, the IP-Address option.Solomon & Glass             Standards Track                     [Page 5]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 1998    4. 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).2. Mobile-IPv4 Configuration Option   This section defines the Mobile-IPv4 Configuration Option and   provides several examples of its use.2.1. Option Format   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     |         Mobile Node's ...   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+         ...  Home Address         |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+       Type      4 (Mobile-IPv4)   Length      6 (The length of this entire extension in bytes)   Mobile Node's Home Address      In a Configure-Request, the IP home address of the mobile node      sending this Configuration Option, otherwise the (unmodified) IP      home address of the mobile node when sent in a Configure-Ack or      Configure-Reject. Configure-Nak'ing this option is undefined and      MUST NOT be sent by implementations complying with this version of      the specification.  This field MUST NOT be zero.   Default Value      The Mobile-IPv4 Configuration Option defaults to the sending      mobile node's home address.   In describing the operation of the Mobile-IPv4 Configuration Option   (in conjunction with the IP-Address Configuration Option), we use the   following abbreviations:Solomon & Glass             Standards Track                     [Page 6]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 1998      PPP Message Types:          Request = Configure-Request           Reject = Configure-Reject              Ack = Configure-Ack              Nak = Configure-Nak      IPCP Configuration Options:            MIPv4 = Mobile-IPv4               IP = IP-Address      IP addresses:          a.b.c.d = some non-zero IP address          w.x.y.z = some non-zero IP address other than a.b.c.d             home = a mobile node's IP Home address              coa = an IP Care-Of Address                0 = the all-zeroes IP address (0.0.0.0)2.2. Overview   The Mobile-IPv4 Configuration Option is designed to be used in   conjunction with the IP-Address Configuration Option.  For the   convenience of implementors, the detailed description insection 2.5   includes all possible combinations of these two options that might be   sent by a PPP peer during IPCP.  Along with each possibility is a   description of how the receiver should interpret the contents as well   as a suggested course of action.2.3. High-Level Requirements for Non-Mobile-Nodes   A node that is not performing mobile node functionality (such as   non-Mobile-IP-aware nodes as well as nodes performing only home agent   functionality, foreign agent functionality, or both) MUST NOT include   a Mobile-IPv4 Configuration Option within any Configure-Request   message.  As per [RFC 1332], such a node SHOULD send a Configure-   Request containing an IP-Address Configuration Option in which the   IP-Address field is set to a non-zero IP address that the node has   assigned to one of its interfaces.  If an explicit IP address has   been assigned to the node's PPP interface then this address SHOULD be   sent in preference to any of the node's other addresses.   A node MUST NOT send a Configure-Nak containing a Mobile-IPv4   Configuration Option.  Doing so is currently "undefined" and might   cause interoperability problems when a useful meaning for Configure-   Nak is ultimately defined for the Mobile-IPv4 Configuration Option.   A node that sends a Configure-Ack containing a Mobile-IPv4   Configuration Option SHOULD send an Agent Advertisement [RFC 2002]   immediately upon IPCP for that link entering the Opened state.Solomon & Glass             Standards Track                     [Page 7]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 19982.4. High-Level Requirements for Mobile Nodes   A mobile node SHOULD begin its IPCP negotiation by sending the   Configure-Request described in either item #1 or item #4 inSection2.5.  The mobile node MAY begin its negotiation with one of the other   numbered items inSection 2.5 under extenuating circumstances.   A mobile node that receives a Configure-Ack containing a Mobile-IPv4   Configuration Option MUST receive an Agent Advertisement, possibly in   response to an Agent Solicitation, before sending a Registration   Request [RFC 2002] if that mobile node is connecting to a foreign   link.  This is because the peer might be a foreign agent that   enforces a policy which requires a mobile node to register with that   foreign agent even if the mobile node is using a co-located care-of   address.  A mobile node need not wait for such an advertisement if it   connects to its home link.  See item 7a insection 2.5 for one way in   which a mobile node can determine if it has connected to its home   link.  Another way is by receiving an explicit notification of this   fact from its peer, such as receipt of the messages in items 1b, 2c,   and 3a insection 2.5.   A mobile node that receives a Configure-Reject containing a Mobile-   IPv4 Configuration Option SHOULD fall back to IPCP negotiation using   the IP-Address option [RFC 1332].  A mobile node SHOULD begin this   negotiation with Request(IP=home) or Request(IP=0), depending on   whether or not the mobile node is connecting to its home link,   respectively.  A mobile node MAY make this determination by   inspection of an IP-Address option contained within a Configure-   Request sent by its peer.  If the prefix of the peer's stated IP-   address is equal to the prefix of the mobile node's home address,   then the mobile node MAY conclude that it is connecting to its home   link.  Otherwise, if the mobile node is connecting to a foreign link,   then the mobile node SHOULD send Request(IP=0) since its peer might   have no means for assigning addresses other than IPCP.  This   specification therefore updates this behavior as described in [RFC   2002], the latter of which recommends that a mobile node begin IP-   Address negotiation with Request(IP=Home) under all circumstances.   A peer that is performing neither home agent nor foreign agent   functionality SHOULD send a Reject in response to any Request   received from its peer that contains a Mobile-IPv4 Configuration   Option.2.5. Detailed Description   The numbered items below show all possible combinations of Mobile-   IPv4 and IP-Address Configuration Options that a mobile node (or a   conventional node) might send to its peer.  Mobile nodes SHOULD beginSolomon & Glass             Standards Track                     [Page 8]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 1998   their IPCP negotiation with item #1 or item #4 depending on whether   they prefer a co-located or a foreign agent care-of address   respectively.  The lettered items list the possible legal responses   that a peer might send to the mobile node (or conventional node) in   response to the numbered Request.   In each case, an interpretation is defined and a suggested course of   action is provided.  Finally, it is believed that the presentation   below has the advantages of conciseness and precision in comparison   to an equivalent presentation in "prose form."    1. Request(IP=0,MIPv4=home) means "I prefer a co-located care-of       address to a foreign agent care-of address."  Peer MUST respond       with one of the following:        a. Nak(IP=coa) means "use coa as your co-located care-of           address".  Goto 2.        b. Nak(IP=home) means "you're at home and don't need a care-of           address".  Goto 3.        c. Reject(IP=0) means "I cannot assign a co-located care-of           address but you're welcome to use me as a foreign agent".           Goto 4.        d. Reject(MIPv4=home) means "I do not implement the Mobile-IPv4           option".  If the peer also sent Request(IP=address) and the           prefix of the peer's assigned address is equal to that of the           mobile node's home address, then goto 6 with a.b.c.d=home;           otherwise, goto 5.        e. Reject(IP=0,MIPv4=home) means "use the default".  Goto 7.        => Ack(IP=0, ...), Nak(MIPv4=any, ...) MUST NOT be sent.    2. Request(IP=coa,MIPv4=home) means "I want to use coa as my co-       located care-of address."  Peer MUST respond with one of the       following:        a. Ack(IP=coa,MIPv4=home) means "ok, use coa as your co-located           care-of address; be sure to wait for an advertisement."           Opened.        b. Nak(IP=alternate-coa) means "no, use alternate-coa as your           co-located care-of address".  Goto 2.        c. Nak(IP=home) means "you're at home and don't need a co-           located care-of address".  Goto 3.        d. Reject(IP=coa) means "coa is not a useful value for a co-           located care-of address on this link and I cannot assign a           useful one (or I will not negotiate the IP-Address option) --           you may use me as a foreign agent".  Goto 4.Solomon & Glass             Standards Track                     [Page 9]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 1998        e. Reject(MIPv4=home) means "I do not implement the Mobile-IPv4           option".  If the peer also sent Request(IP=address) and the           prefix of the peer's address is equal to that of the mobile           node's home address, then goto 6 with a.b.c.d=home;           otherwise, goto 5.        f. Reject(IP=coa,MIPv4=home) means "use the default".  Goto 7.        => Nak(MIPv4=any, ...) MUST NOT be sent.    3. Request(IP=home,MIPv4=home) means "I think I'm at home but if I'm       wrong then I prefer a co-located care-of address to a foreign       agent care-of address."  Peer MUST respond with one of the       following:        a. Ack(IP=home,MIPv4=home) means "yes, you're at home".  Opened.        b. Nak(IP=coa) means "you're not at home, use coa as your co-           located care-of address".  Goto 2.        c. Reject(IP=home) means "you're not at home and I cannot assign           a co-located care-of address (or I will not negotiate the           IP-Address option) -- you may use me as a foreign agent".           Goto 4.        d. Reject(MIPv4=home) means "I do not implement the Mobile-IPv4           option".  If the peer also sent Request(IP=address) and the           prefix of the peer's address is equal to that of the mobile           node's home address, then goto 6 with a.b.c.d=home;           otherwise, goto 5.        e. Reject(IP=home,MIPv4=home) means "use the default".  Goto 7.        => Nak(MIPv4=any, ...) MUST NOT be sent.    4. Request(MIPv4=home) means "I want to run Mobile IP over this link       and I don't want a co-located care-of address." Peer MUST respond       with one of the following:        a. Ack(MIPv4=home) means "ok, wait for an advertisement to           figure out where you are."  Opened.        b. Reject(MIPv4=home) means "I do not implement the Mobile-IPv4           option".  If the peer also sent Request(IP=address) and the           prefix of the peer's address is equal to that of the mobile           node's home address, then goto 6 with a.b.c.d=home;           otherwise, goto 5.        => Nak(MIPv4=any, ...) MUST NOT be sent.    5. Request(IP=0) means "Please assign an address/co-located-care-       of-address".  Peer MUST respond with one of the following:Solomon & Glass             Standards Track                    [Page 10]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 1998        a. Nak(IP=a.b.c.d) means "use a.b.c.d as your address/co-           located-care-of-address".  Goto 6.        b. Reject(IP=0) means "I cannot assign an address (for the           Mobile Node to use as a co-located-care-of-address), or I do           not implement the IP-Address option".  Goto 7.        => Ack(IP=0) MUST NOT be sent and historically means "I don't           know your address either".  Opened.  An implementation MUST           NOT use 0 as its IP address upon receiving Ack(IP=0) but MAY           use some other, non-zero, interface address for packets sent           on its PPP interface.    6. Request(IP=a.b.c.d) means "I want to use a.b.c.d as my       address/home-address/co-located-care-of-address".  Peer MUST       respond with one of the following:        a. Ack(IP=a.b.c.d) means "ok, a.b.c.d is your address/home-           address/co-located-care-of-address".  Opened.        b. Nak(IP=w.x.y.z) means "no, use w.x.y.z as your address/home-           address/co-located-care-of-address".  Goto 6.        c. Reject(IP=a.b.c.d) means "a.b.c.d is a bad address to use,           but I cannot give you a good one" or "I do not implement the           IP-Address option".  Goto 7.    7. Request() means "I want to use the default".  Peer MUST respond       with one of the following:        a. Ack() means "ok, use the default".  Opened.           In this case the mobile node will use the "default" values of           the IP-Address option (no address configured by IPCP) and the           Mobile-IPv4 option (the mobile node's IP home address).  The           mobile node SHOULD send Agent Solicitations to see if there           are any agents present on the current link. (Note that the           current "link" might also include a shared medium if the           mobile node's PPP peer is a bridge.)  If an agent is present           and the mobile node receives an Agent Advertisement, then the           mobile node employs its move-detection algorithm(s) and           registers accordingly.           In any case, if the mobile node's peer supplied an IP-Address           option containing a non-zero value within an IPCP Configure-           Request, the mobile node MAY use this address to determine           whether or not it is connected to its home link.  This can be           accomplished by comparing the stated IP address with the           mobile node's home address under the prefix-length associated           with the home link.  If the mobile node is connected to its           home link then it SHOULD de-register with its home agent.Solomon & Glass             Standards Track                    [Page 11]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 1998           Otherwise, the mobile node MAY attempt to obtain a           topologically routable address through any of its supported           means (e.g., DHCP, manual configuration, etc.)  for use as a           co-located care-of address.  If the mobile node is successful           in obtaining such an address then it SHOULD register this           address with its home agent.        => Nak(IP=0) MUST NOT be sent.  Goto 6.        => Nak() MUST NOT be sent.        => Reject() MUST NOT be sent.2.6. Example Scenarios   This section illustrates the use of the option and protocol as   defined in the previous sections.  In the examples which follow, a   Configure-Request sent by a mobile node and the response generated by   the peer are shown on the same line.  The number and letter to the   left of each request/response refer to the numbered and lettered   items inSection 2.5.    A. A mobile node prefers a co-located care-of address and the peer       is a foreign agent that is capable of assigning such an address:       (1)(a) Request(IP=0,MIPv4=Home) / Nak(IP=coa)       (2)(a) Request(IP=coa,MIPv4=Home) / Ack(IP=coa,MIPv4=Home)         - Mobile node waits to receive an Agent Advertisement.         - If (Advertisement has R-bit set) then             Mobile node registers using co-located care-of address via             the foreign agent;           else             Mobile node registers using co-located care-of address             directly with its home agent.    B. A mobile node prefers a co-located care-of address and the peer       is a foreign agent that cannot assign a co-located care-of       address (e.g., it has no pool of addresses from which to allocate       for the purpose of assignment):       (1)(c) Request(IP=0,MIPv4=Home) / Reject(IP=0)       (4)(a) Request(MIPv4=Home) / Ack(MIPv4=Home)         - IPCP completes.         - Mobile node waits to receive an Agent Advertisement.         - Mobile node registers using the peer's foreign agent care-of           address with its home agent.Solomon & Glass             Standards Track                    [Page 12]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 1998    C. A mobile node prefers a co-located care-of address and the peer       determines that the mobile node's home address is such that the       mobile node is connecting to its home link:       (1)(b) Request(IP=0,MIPv4=Home) / Nak(IP=Home)       (3)(a) Request(IP=Home,MIPv4=Home) / Ack(IP=Home,MIPv4=Home)         - IPCP completes.         - Mobile node de-registers with its home agent.    D. A mobile node prefers a foreign agent care-of address and the       peer is a foreign agent which finds this state of affairs       satisfactory:       (4)(a) Request(MIPv4=Home) / Ack(MIPv4=Home)         - IPCP completes.         - Mobile node waits to receive an Agent Advertisement.         - Mobile node registers using the peer's foreign agent care-of           or de-registers at home, depending on the values in the Agent           Advertisement.    E. A mobile node prefers a co-located care-of address and the peer       does not implement the Mobile-IPv4 Configuration Option.  The       peer is, however, capable of assigning dynamic addresses:       (1)(d) Request(IP=0,MIPv4=Home) / Reject(MIPv4=Home)       (5)(a) Request(IP=0) / Nak(IP=a.b.c.d)       (6)(a) Request(IP=a.b.c.d) / Ack(IP=a.b.c.d)         - IPCP completes.         - Mobile node registers using a.b.c.d as a co-located care-of           address with its home agent.    F. A mobile node prefers a co-located care-of address and the peer       does not implement the Mobile-IPv4 Configuration Option. The peer       is not capable of assigning dynamic addresses:       (1)(e) Request(IP=0,MIPv4=Home) / Reject(IP=0,MIPv4=Home)       (7)(a) Request() / Ack()         - IPCP completes.         - Mobile node sends an Agent Solicitation and/or attempts to           obtain a co-located care-of address via means outside IPCP           (e.g., DHCP or manual configuration), or it gives up.Solomon & Glass             Standards Track                    [Page 13]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 19983. Additional Requirements3.1. Other IPCP Options   A mobile node MUST NOT include the deprecated IP-Addresses option in   any Configure-Request that contains a Mobile-IPv4 option, an IP-   Address option, or both.   Conversely, the mobile node MAY include an IP-Compression-Protocol   option and any other options that do not involve the negotiation of   IP addresses.   If a mobile node and a foreign agent or a 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].  If the PPP peer entities are utilizing VJ header   compression there is no gain for the mobile ip entities to do so, and   requesting this option is likely to cause confusion.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 renegotiate   IPCP at any time, including, the renegotiation of the IP-Address   Configuration Option and the Mobile-IPv4 Configuration Option   described in this document.  As per [RFC 1661], a mobile node in the   Opened state MUST renegotiate IPCP upon receiving an IPCP Configure-   Request from its peer.   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 (seesection 2.4.2 in   [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   (seeSection 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.Solomon & Glass             Standards Track                    [Page 14]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 1998   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 (seeSection 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 SHOULD send an Agent Advertisement over a PPP link   immediately after IPCP for that link enters the Opened state.4. 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.5. References   [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate      Requirement Levels",BCP 14,RFC 2119, March 1997.   [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", STD 51,RFC 1661, July 1994.   [RFC 1827] Atkinson, R., "IP Encapsulating Security Payload (ESP)",RFC 1827, August 1995.Solomon & Glass             Standards Track                    [Page 15]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 1998   [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 1996.6. Acknowledgments   The design of this protocol and option were inspired by an earlier   submission by B. Patel and C. Perkins, then of IBM, in a now expired   internet draft.  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 some of Charlie   Perkins' definitions, and other relavent text, from [RFC 2002].   Tim Wilson and Chris Stanaway (Motorola) contributed significantly to   the design of this Configuration Option and protocol specification.   Special thanks to Vernon Schryver (SGI), Craig Fox (Cisco), Karl Fox   (Ascend), and John Bray (FTP) for their helpful suggestions,   comments, and patience.7. Authors' Addresses   Jim Solomon   Motorola, Inc.   1301 E. Algonquin Rd. - Rm 2240   Schaumburg, IL  60196   Phone:  +1-847-576-2753   Fax:    +1-847-576-3240   EMail:  solomon@comm.mot.com   Steven Glass   FTP Software, Inc.   2 High Street   North Andover, MA  01845   Phone:  +1-508-685-4000   Fax:    +1-508-684-6105   EMail:  glass@ftp.comSolomon & Glass             Standards Track                    [Page 16]

RFC 2290            Mobile-IPv4 Option for PPP IPCP        February 19988.  Full Copyright Statement   Copyright (C) The Internet Society (1998).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Solomon & Glass             Standards Track                    [Page 17]