[Search] [pdf|bibtex] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02                                                      
   Individual Submission                                       B. Haberman
   Internet Draft                                                J. Martin
   draft-haberman-ipngwg-auto-prefix-02.txt
   February 2002
   Expires August 2002


                Automatic Prefix Delegation Protocol for
                   Internet Protocol Version 6 (IPv6)

               <draft-haberman-ipngwg-auto-prefix-02.txt>


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.


Abstract

   The expansion of the IP address space provided by IPv6 makes it both
   possible and reasonable to allocate entire subnets to environments
   that had been previously limited to a few individual IP addresses.
   Other protocols such as Neighbor Discovery and Stateless Address
   Autoconfiguration allow hosts within those subnets to be
   automatically configured. The router between this subnet and the
   upstream world requires just one more piece to make this process
   automatic, a network prefix.

   This document describes a mechanism for the automated delegation of
   an IPv6 network prefix. It allows routers to request either a
   specific prefix or any prefix. Upon authorizing the request the
   delegating router then returns a prefix and a lifetime for the use
   of the prefix.  Optionally, the delegating and requesting routers
   can exchange routing protocol information.



Haberman, Martin                                                     1



Internet Draft      <Automatic Prefix Delegation>       February 2002

1. Introduction

   This specification defines the Prefix Delegation (PD) protocol for
   Internet Protocol Version 6 (IPv6). Routers use Prefix Delegation to
   request a network prefix for use on directly attached networks.
   Upon receipt of the request, the delegating router may authenticate
   the request, and will establish if the requested prefix size is
   acceptable. The delegating router then specifies the prefix for use
   and the length of time for which that prefix is delegated.

   The Prefix Delegation protocol supports extensible options.  These
   options may be used to negotiate additional operational parameters,
   such as routing protocol information.


2. Terminology

  2.1 General

   This document uses the terminology defined in [RFC 2460] and [RFC
   2461] and in addition:

        - Requesting Router - The router that is requesting that a
           prefix be assigned

        - Delegating Router - The router that is responding to the
           prefix request

  2.2 Requirements

   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 [RFC 2119].


3. Scope of Work

   This proposal is meant to give a singly homed leaf router the
   ability to obtain an IPv6 prefix that can be used within its leaf
   network.  Future revisions of this document may support a more
   generic approach to dynamic prefix delegation.

   It is also assumed that the delegating server/router shares a
   network connection with the requesting router.  Future revisions may
   remove this restriction and allow for either multi-hop messages or a
   relay function.


4. Protocol Overview



Haberman, Martin                                                     2



Internet Draft      <Automatic Prefix Delegation>       February 2002

   The Prefix Delegation protocol defines two new ICMP message types,
   the Prefix Request and the Prefix Delegation. The Prefix Request is
   used by the Requesting Router to communicate requests to the
   Delegating Router. Conversely, the Prefix Delegation is used by the
   Delegating Router to communicate prefix and error information with
   the Requesting Router.

  4.1 Delegator Query

   The Requesting Router begins the Prefix Delegation process by
   sending a Prefix Request message of type [DELEGATOR QUERY] to the
   All-Routers link-local multicast address (FF02::2).

   Upon receipt of the Delegator query, a Delegating Router determines
   if it is configured to provide prefixes of the specified scope. If
   so, it unicasts a Prefix Delegation of type [PREFIX DELEGATOR] to
   the Requestor. If not, the message is silently discarded.

   After sending the query, the Requestor waits for Query Interval
   (Default: 5) seconds for one or more Delegating Routers to respond.
   If there is no response, the Delegator Query is sent again up to Max
   Query times (Default: 3). If no response is received, there are no
   Prefix Delegation services available, and Prefix Delegation has
   failed.

   If more than one response is received to the query within the Query
   Interval, the response with the numerically highest source IP
   address is used.

  4.2 Initial Request

   Once a Delegating Router is chosen, the Requestor sends a Prefix
   Request message of type Initial Request to the unicast IP address of
   the chosen Delegating Router.

   The Requestor may or may not have a Security Association with the
   Delegating Router, however if Authentication is required and no SA
   is present, the Delegator will reject the request with an error
   response indicating that Authentication is required. The Requestor
   then builds a Security Association with the Delegator and sends
   another Initial Request including the SA information.

   If no response is heard within Request Timeout seconds (Default: 5),
   the Initial Request should be sent again, up to Max Initial Request
   (Default: 3) tries. If no response is heard, a Delegator Query is
   sent and the process restarted. If this cycle is repeated Max
   Delegation Attempts times (Default: 3), Prefix Delegation has
   failed.

  4.3 Message Security


Haberman, Martin                                                     3



Internet Draft      <Automatic Prefix Delegation>       February 2002

   Upon receipt of the Prefix Request of any type, the Delegating
   Router establishes if there is a need for Authentication and/or
   Encryption, based upon local policy. If either is required and none
   is provided, the Delegator will return a Prefix Delegation message,
   with a code of Authentication Required.

   The building of a Security Association between the Delegator and the
   Requestor is based on the Authentication and/or Encapsulated
   Security Payload extension headers defined in [RFC 2402] and [RFC
   2406].

  4.4 Prefix Delegation

   After the request is verified to be acceptable, the Delegating
   Router allocates the requested prefix size from its pool of
   available addresses. The creation and management of that pool is
   beyond the scope of this document, but it can be supposed that
   minimalistically a Delegating Router will be statically configured
   with a fixed pool. If no acceptable prefix is available, a Prefix
   Delegation message with a code of Prefix Unavailable is returned.

   The Delegating Router then sends a Prefix Delegation message to the
   Requesting Router containing a code of Prefix Delegation and all of
   the prefix information.  The Requesting Router then activates the
   prefix on its interface of choice.

  4.5 Prefix Refresh

   All Prefix Delegations have a lifetime that MUST follow the rules
   defined in Section 4.6.2 of [RFC 2461].  Upon receiving a Prefix
   Delegation, the requesting router initiates a timer such that before
   the lifetime expires, the Requesting Router sends a Prefix Request
   with code=REFRESH directly to the Delegating router.

   If the Requestor receives no response within [RENEWAL TIMEOUT]
   seconds (Default: 5), the Renewal Request should be sent again, up
   to [MAX RENEWAL REQUEST] (Default: 3) tries.  If no response is
   heard the previously allocated prefix is not renewed.

   A Requesting Router receiving the Prefix Unavailable code, or no
   response at all, has not had the prefix renewed.  It will expire at
   the end of the initial lifetime.  To acquire a new prefix, the
   Requesting Router must begin anew as described in Section 4.1.

  4.6 Prefix Return

   If the Requesting Router no longer requires the use of a prefix, it
   can return that prefix to the control of the Delegating Router
   through the use of the Prefix Return code in a Prefix Request. The
   requesting router sends a Prefix Request directly to the Delegating
   Router.

Haberman, Martin                                                     4



Internet Draft      <Automatic Prefix Delegation>       February 2002


   Upon receipt and verification (if needed) of this message, the
   Delegating Router returns the prefix to the pool and issues a Prefix
   Delegation with a code of Prefix Returned.

5. Messages

   All messages have the following general format:


      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      |     Code      |          Checksum             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                          Message Body                         +
     |                                                               |


   The following sections describe the specific messages and options
   used in delegating IPv6 prefixes.

  5.1 Prefix Request Message

   The Prefix Request Message is sent to request, renew, or release a
   prefix.


   IP Fields

      Source Address
          An IP address assigned to the sending interface.

      Destination Address
          The All-Routers link-local multicast address (FF02::2)for
          Delegator Query messages. All other Prefix Request messages
          should be sent to a unicast address of the Delegating Router.

      Authentication Header
          If a Security Association for the IP Authentication Header
          exists between the sender and the destination address, then
          the sender SHOULD include this header. No such header is
          required for the initial prefix request that is multicast,
          but may be required for further progress.

    ICMP Fields

      Type
          XXX (Where XXX is assigned by IANA)


Haberman, Martin                                                     5



Internet Draft      <Automatic Prefix Delegation>       February 2002

      Code
          They Type of Request Code:

          Delegator Query (0)
                The Delegator Query is used by the Requestor to
                identify potential Delegating Routers. It is sent to
                the All-Routers link-local multicast address with no
                Authentication Header.

          Initial Request (1)
                The Initial Request is used to initiate the request
                process. It is sent to the unicast IP address of the
                Delegating Router, and may carry an Authentication
                Header. Unused fields MUST be set to zero.  An Initial
                Request code MAY contain a Prefix Option.

          Renewal Request (2)
                The Renewal Request is used to renew a prefix that has
                been previously allocated.  It is sent to a unicast IP
                address of the Delegating Router and may carry an
                Authentication Header.  A Renewal Request code MUST
                contain at least one Prefix Option.

          Prefix Return (3)
                The Prefix Return is used to return an unused prefix,
                or portion of a prefix to the control of the Delegating
                Router. It is sent to a unicast IP address of the
                Delegating Router and may carry an Authentication
                Header.  A Prefix Return code MUST contain at least one
                Prefix Option.

      Checksum
          The ICMP checksum as defined in [RFC 2463].

  5.2 Prefix Delegation Message Format

   The Prefix Delegation Messages are sent to provide the addresses of
   available Prefix Delegators, to provide prefix data, and for error
   returns.


   IP Fields

      Source Address
          An IP address assigned to the sending interface.

      Destination Address
          The IP address of the Requestor as specified by the IP Source
          Address in the Prefix Request message.

      Authentication Header


Haberman, Martin                                                     6



Internet Draft      <Automatic Prefix Delegation>       February 2002

          If a Security Association for the IP Authentication Header
          exists between the sender and the destination address, then
          the sender SHOULD include this header.

    ICMP Fields

      Type
          XXX+1 (Where XXX+1 is assigned by IANA)

      Code
          The Type of Response Code:

          Prefix Delegator (0)
                The Prefix Delegator is used by the Delegator to inform
                the Requestor that it is available to provide prefixes
                of the desired type. It is sent to the unicast IP
                address in the Source Address portion of the Prefix
                Request packet. Unused fields MUST be set to zero.

          Authentication Required (1)
                The Authentication Required message indicates to the
                Requestor that a Security Association must be
                established before a prefix can be delegated. It is
                sent to the unicast IP address in the Source Address
                portion of the Prefix Request packet. Unused fields
                MUST be set to zero.

          Authorization Failed (2)
                The Authorization Failed message indicates to the
                Requestor that either it is not authorized to request a
                prefix, or that the prefix requested fell outside of
                local policy. It is sent to the unicast IP address in
                the Source Address portion of the Prefix Request
                packet. Unused fields MUST be set to zero.

          Prefix Unavailable (3)
                The Prefix Unavailable indicates that the Prefix
                Request was acceptable, but the Delegator does not have
                sufficient available address space to fulfill the
                request.  It is sent to the unicast IP address in the
                Source Address portion of the Prefix Request packet.
                Unused fields MUST be set to zero.

          Prefix Delegated (4)
                The Prefix Delegated message actually provides the
                prefix information that the Requestor has requested. It
                is sent to the unicast IP address in the Source Address
                portion of the Prefix Request packet. For this message,
                a Prefix Option MUST be included.

          Prefix Returned (5)


Haberman, Martin                                                     7



Internet Draft      <Automatic Prefix Delegation>       February 2002

                The Prefix Return is used to confirm the return of a
                prefix. It is sent to the unicast IP address in the
                Source Address portion of the Prefix Request packet.
                For this message, the Prefix Option MUST be included.

      Checksum
          The ICMP checksum.

  5.3 Prefix Option

   The Subnet Prefix Option is used to relay prefix information between
   Requestors and Delegators.  It has the following format:


      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             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Prefix Lifetime                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +                                                               +
     |                                                               |
     +                             Prefix                            +
     |                                                               |
     +                                                               +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    Prefix Option Fields

      Type = 0x01
          This field identifies the presence of a subnet prefix.  This
          option MUST follow either a Prefix Request header or a Prefix
          Delegation header.

      Length
          The length of the prefix contained in the option.

      Reserved
          This field is unused. It MUST be initialized to zero by the
          sender and MUST be ignored by the receiver.

      Prefix Lifetime
          The lifetime of the prefix contained in the option.

      IPv6 Prefix
          The Prefix field is used to carry a subnet prefix. The host
          portion of the IP address MUST be padded with zeros.


Haberman, Martin                                                     8



Internet Draft      <Automatic Prefix Delegation>       February 2002


6. Security Considerations

   The ability to automate the delegation of prefixes opens several
   security vulnerabilities.  Rogue delegators can issue bogus prefixes
   to requestors.  This may cause denial of service due to
   unreachability.  Rogue requestors may consume valuable resources
   from legitimate delegators, thus denying others the use of the
   prefixes.  For these reasons, the use of IPSec-based Authentication
   and/or Encryption is suggested.

7. To Do's

   - Additional security discussion
   - Relay functionality
   - Routing capabilities option

8. Acknowledgements

   We would like to acknowledge and thank Jun-ichiro itojun Hagino,
   Dave Thaler, Yamasaki Toshi, Ole Troan, and Kazuaki Tsuchiya for
   their feedback and suggestions on this document.

9. References


   [RFC 2460] S. Deering and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC 2461] T. Narten, E. Nordmark, and W. Simpson, "Neighbor
              Discovery for IP Version 6 (IPv6)", RFC 2461, December
              1998.

   [RFC 2119] S. Bradner, "Key words for use in RFCs to Indicate
              Requirement Levels", RFC 2119, BCP 14, March 1997.

   [RFC 2463] A. Conta and S. Deering, "Internet Control Message
              Protocol (ICMPv6) for the Internet Protocol Version 6
              (IPv6) Specification", RFC 2463, December 1998.


Authors' Addresses

   Brian Haberman
   haberman@lorien.sc.innovationslab.net

   Jim Martin
   jim@interop.net




Haberman, Martin                                                     9