rfc2794.txt

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Network  Working Group                                         P. Calhoun
Request for Comments: 2794                  Sun Microsystems Laboratories
Updates: 2290                                                  C. Perkins
Category: Standards Track                           Nokia Research Center
                                                               March 2000


         Mobile IP Network Access Identifier Extension for IPv4

Status 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 (2000).  All Rights Reserved.

Abstract

   AAA servers are in use within the Internet today to provide
   authentication and authorization services for dial-up computers.
   Such services are likely to be equally valuable for mobile nodes
   using Mobile IP when the nodes are attempting to connect to foreign
   domains with AAA servers.  AAA servers today identify clients by
   using the Network Access Identifier (NAI). Our proposal defines a way
   for the mobile node to identify itself, by including the NAI along
   with the Mobile IP Registration Request.  This memo also updates RFC
   2290 which specifies the Mobile-IPv4 Configuration option for IPCP,
   by allowing the Mobile Node's Home Address field of this option to be
   zero.

















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RFC 2794                    Mobile Node NAI                   March 2000


1. Introduction

   AAA servers are in use within the Internet today to provide
   authentication and authorization services for dial-up computers.
   Such services are likely to be equally valuable for mobile nodes
   using Mobile IP when the nodes are attempting to connect to foreign
   domains with AAA servers.  AAA servers today identify clients by
   using the Network Access Identifier (NAI) [1].  This document
   specifies the Mobile Node NAI extension to the Mobile IP Registration
   Request [7] message from the mobile node.

   Since the NAI is typically used to uniquely identify the mobile node,
   the mobile node's home address is not always necessary to provide
   that function.  Thus, it is possible for a mobile node to
   authenticate itself, and be authorized for connection to the foreign
   domain, without even having a home address.  A message containing the
   Mobile Node NAI extension MAY set the Home Address field to zero (0)
   in the Registration Request, to request that a home address be
   assigned.

   The "Mobile-IPv4 Configuration" option to IPCP has been specified in
   RFC 2290 [8] for proper interaction between a mobile node and a peer,
   through which the mobile node connects to the network using PPP.
   According to that specification the Mobile Node's Home Address field
   of the option MUST not be zero.  However, in the context of this memo
   which allows a mobile node to be identified by its NAI and to obtain
   an address after the PPP phase of connection establishment, the Home
   Address field is allowed to be zero while maintaining all other
   aspects of RFC 2290.  Interpretation of various scenarios from RFC
   2290 is given in section 4.

   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 in [3].

2. Mobile Node NAI Extension

   The Mobile Node NAI extension, shown in figure 1, contains the user
   name following the format defined in [1].  When it is present in the
   Registration Request, the Home Address field MAY be set to zero (0).
   The Mobile Node NAI extension MUST appear in the Registration Request
   before both the Mobile-Home Authentication extension and Mobile-
   Foreign Authentication extension, if present.








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RFC 2794                    Mobile Node NAI                   March 2000


       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     |           MN-NAI ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 1: The Mobile Node NAI Extension


      Type       131 (skippable) [7]

      Length     The length in bytes of the MN-NAI field

      MN-NAI     A string in the NAI format defined in [1].

3. Foreign Agent Considerations

   If Home Address is zero in the Registration Request, the foreign
   agent MUST use the NAI instead in its pending registration request
   records, along with the Identification field as usual.  If the
   foreign agent cannot manage pending registration request records in
   this way, it MUST return a Registration Reply with Code indicating
   NONZERO_HOMEADDR_REQD (see section 5).

   If the mobile node includes the Mobile Node NAI extension in its
   Registration Request, then the Registration Reply from the home agent
   MUST include the Mobile Node NAI extension.  If not, the foreign
   agent SHOULD send the Registration Reply to the mobile node, changing
   the Code to the value MISSING_NAI (see section 5).  The Registration
   Reply MUST include a nonzero Home Agent address and mobile node's
   Home Address.  If not, the foreign agent SHOULD send the Registration
   Reply to the mobile node, changing the Code to the value
   MISSING_HOME_AGENT or MISSING_HOMEADDR, respectively (see section 5).

4. Interactions with Mobile-IPv4 Configuration Option to IPCP

   In the Mobile-IPv4 Configuration Option to IPCP [8], the Mobile
   Node's Home Address field may be zero.  In this section, we specify
   the action to be taken in that case, when the mobile node is using
   the Mobile Node NAI extension in the Mobile IP Registration Request.
   Whether or not the IP Address Configuration Option contains a nonzero
   IP address, the mobile node will subsequently attempt to obtain a
   home address from the Mobile IP Registration Reply.

   If the IP Address Configuration Option to IPCP has IP address equal
   to zero, the PPP peer is expected to allocate and assign a co-located
   care-of address to the Mobile Node.  If, on the other hand, the IP




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RFC 2794                    Mobile Node NAI                   March 2000


   Address Configuration Option to IPCP has a nonzero IP address, the
   PPP peer is expected to assign that address to the Mobile Node as its
   co-located care-of address.

   Finally, if the IP Address Configuration Option is left out of the
   IPCP Configure-Request, then no co-located care of address is
   assigned during IPCP. The mobile node will acquire a co-located care
   of address during a later stage of configuration or will use an FA-
   located care-of address.

5. Error Values

   Each entry in the following table contains the name and value for the
   Code [7] to be returned in a Registration Reply, and the section in
   which the error Code is first mentioned in this specification.

      Error Name               Value   Section of Document
      ----------------------   -----   -------------------
      NONZERO_HOMEADDR_REQD    96      3
      MISSING_NAI              97      3
      MISSING_HOME_AGENT       98      3
      MISSING_HOMEADDR         99      3

6. IANA Considerations

   The Mobile Node NAI extension defined in Section 2 is a Mobile IP
   registration extension as defined in RFC 2002 [7] and extended in RFC
   2356 [6].  IANA should assign a value of 131 for this purpose.

   The Code values defined in Section 5 are error codes as defined in
   RFC 2002 and extended in RFC 2344 [5] and RFC 2356 [6].  They
   correspond to error values conventionally associated with rejection
   by the foreign agent (i.e., values from the range 64-127).  IANA
   should record the values as defined in Section 5.

7. Security Considerations

   Mobile IP registration messages are authenticated, and the
   authentication verified by the recipient.  This proposal does not
   prohibit the mobile node from sending its NAI in the clear over the
   network, but that is not expected to be a security issue.

8. IPv6 Considerations

   Supporting NAI-based registrations for Mobile IPv6 [4] is outside the
   scope of this document.  This section contains some ideas how
   Stateless Address Autoconfiguration [9] and DHCPv6 [2] might be
   extended to support NAI-based Mobile IPv6 registrations.



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RFC 2794                    Mobile Node NAI                   March 2000


   For mobile nodes using IPv6, there are no commonly deployed
   mechanisms by which a mobile node may present its credentials, such
   as exist today with IPv4.  Nevertheless, a mobile node using IPv6
   mobility may wish to specify the domain in which their credentials
   may be checked, by using a NAI just as this specification proposes
   for IPv4.  In the case of IPv6, however, there is no foreign agent in
   place to manage the connectivity of the mobile node, and thus to
   manage the verification of the credentials offered by the mobile
   node.  To identify the HDAF (see appendix A) that has the expected
   relationship with the mobile node, the NAI would have to be forwarded
   to a local AAA by the local agent involved with configuring the
   care-of address of the mobile node.

   This agent can either be a router sending out Router Advertisements
   [9], or a DHCPv6 server.  In the former case, the router could signal
   its ability to handle the NAI by attaching some yet to be defined
   option to the Router Advertisement.  In the latter case, for managed
   links, the mobile node could include a yet to be defined NAI
   extension in its DHCP Solicitation message.  Such an NAI extension
   and appropriate authentication would also be required on the
   subsequent DHCP Request sent by the mobile node to the DHCP Server
   selected on the basis of received DHCP Advertisements.  Once a care-
   of address on the foreign network has been obtained, the mobile node
   can use regular MIPv6 [4].