rfc2290.txt

RFC 的详细文档！

      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 in section 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 1998


2.4. 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 in Section
   2.5.  The mobile node MAY begin its negotiation with one of the other
   numbered items in Section 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 in section 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 in section 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 begin



Solomon & 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