Cisco's Mobile IPv4 Host Configuration Extensions
RFC 4332

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Network Working Group                                           K. Leung
Request for Comments: 4332                                      A. Patel
Category: Informational                                    Cisco Systems
                                                             G. Tsirtsis
                                                    Flarion Technologies
                                                             E. Klovning
                                                 Birdstep Technology ASA
                                                           December 2005

           Cisco's Mobile IPv4 Host Configuration Extensions

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

IESG Note

   This RFC is not a candidate for any level of Internet Standard.  The
   IETF disclaims any knowledge of the fitness of this RFC for any
   purpose and in particular notes that the decision to publish is not
   based on IETF review for such things as security, congestion control,
   or inappropriate interaction with deployed protocols.  The RFC Editor
   has chosen to publish this document at its discretion.  Readers of
   this document should exercise caution in evaluating its value for
   implementation and deployment.  See RFC 3932 for more information.

   This RFC does not offer any security mechanisms to provide data
   origin authentication and integrity, yet these security services are
   vitally important in this context.

Abstract

   An IP device requires basic host configuration to be able to
   communicate.  For example, it will typically require an IP address
   and the address of a DNS server.  This information is configured
   statically or obtained dynamically using Dynamic Host Configuration
   Protocol (DHCP) or Point-to-Point Protocol/IP Control Protocol
   (PPP/IPCP).  However, both DHCP and PPP/IPCP provide host
   configuration based on the access network.  In Mobile IPv4, the
   registration process boots up a Mobile Node at an access network,
   also known as a foreign network.  The information to configure the

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RFC 4332                      Host Config                  December 2005

   host needs to be based on the home network.  This document describes
   the Cisco vendor-specific extensions to Mobile IPv4 to provide the
   base host configuration in Registration Request and Reply messages.

Table of Contents

   1. Introduction ....................................................2
   2. Host Configuration Extensions Summary ...........................3
   3. Host Configuration Extensions ...................................4
      3.1. Host Configuration Request Extension .......................5
      3.2. Home Network Length Prefix Extension .......................5
      3.3. DNS Server Extension .......................................6
      3.4. DHCP Server Extension ......................................6
      3.5. DHCP Client ID Extension ...................................7
      3.6. Default Gateway Extension ..................................7
      3.7. DNS Suffix Extension .......................................8
      3.8. Configuration URL Extension ................................8
   4. Security Considerations .........................................9
   5. Acknowledgements ................................................9
   6. Informative References ..........................................9

1.  Introduction

   An IPv4 device requires some basic configuration to communicate with
   other nodes.  Typically, it has an IP address for an interface and
   DNS server's IP address to resolve the peer's hostname to an IP
   address.  DHCP [RFC2131] and PPP/IPCP [RFC1332] provide host
   configuration information on the access network interface, but this
   is inadequate in a Mobile IPv4 environment.  In Mobile IPv4
   [RFC3344], a Mobile Node has a virtual network interface on the home
   network, anchored by the Home Agent.  The IP address, home subnet
   prefix, default gateway, and home network's DNS servers are essential
   in the boot up of a network interface.  In some cases, these are the
   only pieces of information needed by the Mobile Node.

   The Mobile IPv4 registration process provides the mechanism for a
   Mobile Node to boot up on a foreign network.  Upon the successful
   registration, the Mobile Node can communicate with the Correspondent
   Node.  The need to provide an efficient method to obtain the host
   configuration exists.  If the Mobile Node is a DHCP client, it can
   obtain configuration parameters from the DHCP server in the home
   network after the initial registration.

   This document introduces the Cisco vendor-specific extensions (VSEs)
   [RFC3115] to provide the means for a Mobile Node to download some
   fundamental configuration associated with the home network via the

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   Home Agent.  These extensions provide information for home subnet
   prefix, DNS server, DHCP server, DHCP client identifier, default
   gateway, DNS suffix, and configuration URL.

2.  Host Configuration Extensions Summary

   The following Cisco vendor-specific extensions provide the host
   configuration for a Mobile Node.  The "Host Configuration Request"
   extension is allowed only in the Registration Request.  The rest of
   the extensions are appended in the Registration Reply.

   o  Host Configuration Request

      *  Request for host configuration information from the Mobile Node
         to the Home Agent.

   o  Home Network Prefix Length

      *  The length of the subnet prefix on the home network.

   o  Default Gateway

      *  The default gateway's IP address on the home network.

   o  DNS Server

      *  The DNS server's IP address in the home network.

   o  DNS Suffix

      *  The DNS suffix for hostname resolution in the home network.

   o  DHCP Client ID

      *  The DHCP Client ID used to obtain the IP address.  When the
         Mobile Node returns home and is responsible for managing its
         own address, this information maps to the client identifier
         option as defined in section 9.14 of [RFC2132] and referenced
         in [RFC2131].

   o  DHCP Server

      *  The DHCP server's IP address in the home network.

   o  Configuration URL

      *  The URL for the Mobile Node to download configuration
         parameters from a server.

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   When the Mobile Node needs to obtain its host configuration, the Host
   Configuration Request VSE is appended to the Registration Request.
   This VSE indicates to the Home Agent that either all or selected host
   configuration VSEs need to be appended to the Registration Reply.  If
   the Home Agent retrieved the information from a DHCP server (in Proxy
   DHCP mode), then the DHCP Client ID and DHCP Server extensions are
   appended in the Registration Reply.  These DHCP-related extensions
   are populated with values that had been used in the DHCP messages
   exchanged between the Home Agent and the DHCP server.

   The VSEs are authenticated as part of the registration message using
   any of the authentication mechanism defined for Mobile IP ([RFC3344],
   [RFC3012]).

   This message MAY contain extensions defined in Mobile IP, including
   vendor-specific extensions [RFC3115].

3.  Host Configuration Extensions

   Cisco's host configuration extensions to Mobile IPv4 are based on the
   vendor-specific extensions defined in [RFC3115].  The format of the
   VSE TLV (Type-Length-Value) is 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      |          Reserved             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Vendor/Org-ID                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       Vendor-NVSE-Type        |     Vendor-NVSE-Value ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Type: 134

     Length:

        Indicates the length (in bytes) of the data field within this
        extension, excluding the Type and Length fields.

     Reserved:

        Reserved for future use.  To be set to 0 while sending, ignored
        on reception.

     Vendor/Org-ID:

        9 (Cisco Systems)

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     Vendor-NVSE-Type:

        14 (Host Configuration)

     Vendor-NVSE-Value:

        Format is shown below for each subtype.  The Sub-Type field is
        an integer from 0 to 255.

3.1.  Host Configuration Request Extension

   This format of the Host Configuration Request extension is shown
   below.

     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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Sub-Type            |           Selector            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Sub-Type:

         0

      Selector:

         0 indicates all host configuration available to the Home
         Agent (HA) is requested by the Mobile Node.

3.2.  Home Network Length Prefix Extension

   This format of the Home Network Prefix Length extension is shown
   below.

     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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Sub-Type            |        Prefix Length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Sub-Type:

         1

      Prefix Length:

         The number of bits in the home subnet prefix.

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3.3.  DNS Server Extension

   This format of the DNS Server extension is shown below.

     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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Sub-Type            |        Primary DNS Server
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 . . .               |        Secondary DNS Server
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 . . .               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Sub-Type:

         2

      Primary DNS Server:

         The IP address of the primary DNS server.

      Secondary DNS Server:

         The IP address of the secondary DNS server.

3.4.  DHCP Server Extension

   This format of the DHCP Server extension is shown below.

     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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Sub-Type            |          DHCP Server
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 . . .               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Sub-Type:

         3

      DHCP Server:

         The IP address of the DHCP server.

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3.5.  DHCP Client ID Extension

   This format of the DHCP Client ID extension is shown below.

     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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Sub-Type            |          Client ID . . .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Sub-Type:

         4

      Client ID:

         DHCP servers use this value to index their database of address
         bindings.  This value is expected to be unique for all clients
         in an administrative domain.  The size of field is between 2
         and 255 octets.

3.6.  Default Gateway Extension

   This format of the Default Gateway extension is shown below.

     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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Sub-Type            |          Default Gateway
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 . . .               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Sub-Type:

         5

      Default Gateway:

         The IP address of the default gateway for the Mobile Node on
         the home network.

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3.7.  DNS Suffix Extension

   This format of the DNS Suffix extension is shown below.

     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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Sub-Type            |         DNS Suffix . . .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Sub-Type:

         6

      DNS Suffix:

         The DNS suffix to be appended to the name of Mobile Node when
         completing its fully qualified domain name (FQDN).  The size of
         field is between 1 and 246 octets.

3.8.  Configuration URL Extension

   This format of the Configuration URL extension is shown below.

     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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Sub-Type            |         URL String . . .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Sub-Type:

         7

      URL String:

         The Mobile Node can retrieve configuration parameters via the
         URL.  The URL is at most 246 bytes in length.

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4.  Security Considerations

   The host configuration extensions follow the same rules for Mobile IP
   extensions in registration messages.  See the Security Considerations
   section in RFC 3344.

   The Configuration URL extension may trigger the Mobile Node to
   download the configuration parameters from a server.  The protection
   of the data transfer is outside the scope of this document.  Possible
   options include encryption of data before transfer or using HTTPS.

5.  Acknowledgements

   The authors would like to acknowledge Jayshree Bharatia, Kuntal
   Chowdhury, Avi Lior, and Lila Madour for their contributions to the
   work in progress titled "Mobile IPv4 Extension for Configuration
   Options Exchange".

6.  Informative References

   [RFC1332]  McGregor, G., "The PPP Internet Protocol Control Protocol
              (IPCP)", RFC 1332, May 1992.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, March 1997.

   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
              Extensions", RFC 2132, March 1997.

   [RFC3012]  Perkins, C. and P. Calhoun, "Mobile IPv4 Challenge/
              Response Extensions", RFC 3012, November 2000.

   [RFC3115]  Dommety, G. and K. Leung, "Mobile IP Vendor/
              Organization-Specific Extensions", RFC 3115, April 2001.

   [RFC3344]  Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
              August 2002.

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Authors' Addresses

   Kent Leung
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   US

   Phone: +1 408-526-5030
   EMail: kleung@cisco.com

   Alpesh Patel
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   US

   Phone: +1 408-853-9580
   EMail: alpesh@cisco.com

   George Tsirtsis
   Flarion Technologies
   Bedminster One
   135 Route 202/206 South
   Bedminster, NJ  07921
   US

   Phone: +1 908-947-7059
   EMail: g.tsirtsis@flarion.com

   Espen Klovning
   Birdstep Technology ASA
   Bryggegata 7
   Oslo,   0250
   Norway

   Phone: +47 95 20 26 29
   EMail: espen@birdstep.com

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   Copyright (C) The Internet Society (2005).

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