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Network Working Group                                       B. Carpenter
Internet-Draft                                         Univ. of Auckland
Intended status: Standards Track                                S. Jiang
Expires: December 9, 2010                   Huawei Technologies Co., Ltd
                                                            June 7, 2010

   Legacy NAT Traversal for IPv6: Simple Address Mapping for Premises
                       Legacy Equipment (SAMPLE)


   IPv6 deployment is delayed by the existence of millions of subscriber
   network address translators (NATs) that cannot be upgraded to support
   IPv6.  This document specifies a mechanism for traversal of such
   NATs.  It is based on an address mapping and on a mechanism whereby
   suitably upgraded hosts behind a NAT may obtain IPv6 connectivity via
   a stateless server, known as a SAMPLE server, operated by their
   Internet Service Provider.  SAMPLE is an alternative to the Teredo

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on December 9, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Normative Notation  . . . . . . . . . . . . . . . . . . . . . . 4
   3.  Detailed specification  . . . . . . . . . . . . . . . . . . . . 4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   7.  Change log  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Appendix A.  Main differences from Teredo . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9

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1.  Introduction

   At the moment, there are two traversal techniques for IPv6 users who
   find themselves behind Customer Premises Equipments (CPEs) which are
   in fact Network Address Translators (NAT) supporting only IPv4:
   1.  A configured tunnel (IPv6 in IPv4 or even IPv6 in UDP), involving
       a managed tunnel broker, e.g.  [RFC3053], with which the user
       must register.  Well known examples include deployments of the
       Hexago tool, and the SixXs collaboration.  However, this approach
       does not scale well; it requires significant support effort and
       is really only suitable for "hobbyist" early adopters of IPv6.
   2.  Teredo [RFC4380].  This is an automatic UDP-based tunneling
       solution that relies on a Teredo server, and on Teredo relays
       willing to carry the traffic.  Unfortunately experience shows
       that this is sometimes an unreliable process in practice, with
       clients sometimes believing that they have Teredo connectivity
       when in fact they don't, or alternatively with the Teredo server
       and relay being very remote from the client and causing extremely
       long latency for IPv6 packets.  This leads to user frustration
       and even to advice from help desks to disable IPv6.

   It is well established that IPv4-only CPEs are the worst product
   related deployment problem for IPv6 [I-D.ietf-v6ops-isp-scenarios],
   and it is also clear that it will be many years before such CPEs,
   being consumer devices sold in millions, will all be replaced.
   Therefore, a scaleable and reliable method for IPv6 traversal of such
   CPEs is desirable.

   The method described here uses a subset of the stateless address
   mapping (SAM) mechanism proposed by [I-D.despres-softwire-sam] and
   elements of the Teredo method.  However, it is intrinsically much
   simpler than Teredo, since it is designed for managed deployment by
   an ISP and its own clients.  The authors understand that an
   alternative formulation of this idea, explicitly in terms of the SAM
   model, may also be published.  The idea is also quite similar to
   [I-D.lee-softwire-6rd-udp] and is published in a preliminary form so
   that the community can evaluate the alternatives.

   The method is intended for explicit adoption by an Internet Service
   Provider (ISP) that wishes to provide IPv6 service to customers
   behind IPv4-only CPE NATs, the common case today.  The method is
   called Simple Address Mapping for Premises Legacy Equipment (SAMPLE).
   The ISP is required to operate a SAMPLE server and (unless operating
   system implementers choose to support SAMPLE directly) to provide
   customers with downloadable code for popular operating systems.  The
   SAMPLE download will create a virtual IPv6 interface on top of the
   real IPv4 interface (just as Teredo, 6to4 and tunnel broker clients
   do).  This is suggested to be a more practical alternative than

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   requiring all customers to replace their CPE.  However, customers
   with an unsuitable operating system, or unwilling to install a
   download, will be advised to buy an IPv6-capable CPE.

   The following figure illustrates the method symbolically:

           Host                 CPE/NAT               SAMPLE
        ___________           ___________          ___________
       | v6|   | V4|         | V4|   | V4|        | V4|   | V6|
       |   |EN |   | Private |   |   |   | Native |   |EN |   | Native
       | S |DE | S | IPv4    | S | N | S | IPv4   | S |DE | S | IPv6
       | T | C | T |---------| T | A | T |--------| T | C | T |------
       | A | A | A |         | A | T | A |        | A | A | A |
       | C | P | C |         | C | 4 | C |        | C | P | C |
       | K |   | K |         | K | 4 | K |        | K |   | K |
       |___|___|___|         |___|___|___|        |___|___|___|

              - Customer IPv4 -         - ISP IPv4 -
                address realm           address realm

   The principle of operation is that each host that starts IPv6
   communication via the SAMPLE server is assigned an IPv6 address which
   forms part of the ISP's regular routeable IPv6 address space.  This
   address embeds the NAT's native IPv4 address (assigned from the ISP's
   IPv4 address space).  It also embeds the port number assigned to the
   IPv6 communication stream by the NAT.  Note that this applies even if
   the ISP is using private addressing itself; the ISP IPv4 address
   realm does not need to use global addresses.  Needless to say, all
   IPv6 addresses are globally unique.

2.  Normative Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  Detailed specification

   The IPv6 address assigned to a host is mapped as follows:
   o  Let PSAMPLE be a /64 IPv6 prefix assigned to the SAMPLE server.
      It may be any native IPv6 prefix chosen out of the routeable
      address space assigned to the ISP.

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   o  Let V4ADDR be the /32 native IPv4 address assigned by the ISP to
      the CPE.
   o  Let PN be the external 16 bit port number assigned by the legacy
      CPE NAT to the host's SAMPLE interface when it first sends traffic
      to the SAMPLE server.  (See below.)

   (Note that the private IPv4 address assigned to the host behind the
   NAT is of no importance in the mapping.)

   The IPv6 address assigned to the host is the concatenation:

       0                           64      80     96
      |          PSAMPLE          | FILL  | PN   | V4ADDR      |

   There is no restriction on the 16 FILL bits except that they MUST
   respect [RFC4291].

   IPv6 packets travelling between the host and the SAMPLE server in
   either direction MUST be encapsulated in UDP as described in
   [RFC4380].  At the host, they are decapsulated and processed by the
   local IPv6 stack.  At the SAMPLE server, they are decapsulated and
   forwarded into the native IPv6 network.  No state is required in the
   SAMPLE server; it performs blind encapsulation and decapsulation.

   The SAMPLE interface in the host MUST be configured with the IPv4
   address and UDP listener port number of the SAMPLE server.  Apart
   from this, it performs blind encapsulation and decapsulation, once it
   has been assigned an IPv6 address.

   [COMMENT: We don't want any sloppiness about reachability of the
   server - so an anycast address used by default seems like a really
   Bad Idea, judging by 6to4 experience.]

   [QUESTION: Do we need a registered port number for this, or is it OK
   to make it configured?  Or, could we re-use the Teredo listener port,

   When a host's SAMPLE interface starts up, it MUST send a Router
   Solicitation message to the SAMPLE server.  The details are as for
   Teredo, except that there is no equivalent of the 'cone' bit
   procedure.  Either the SAMPLE server will reply with a Router
   Advertisement within a timeout TBD, or the method will fail.

   Teredo's Origin Indication mechanism is used to convey the values of
   PN and V4ADDR with the Router Advertisement.  The SAMPLE interface
   can complete its own configuration upon receipt of such an RA

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   Once an IPv6 address has been configured, the SAMPLE interface MUST
   send "keep alive" probes to the SAMPLE server whenever there has been
   no traffic through the interface for TBD seconds, in order to keep
   the relevant NAT state alive.

   [COMMENT: Need to specify that in detail.  Probably, the probe can
   simply be a "no next header" IPv6 packet, and the timeout will be
   configured to a value determined by experience.]

   The SAMPLE server will act as an IPv6 router.  In the simplest case,
   it will forward all IPv6 packets to a default route, except those
   whose destination address lies within the PSAMPLE prefix, which will
   be encapsulated and sent towards the host (CPE) and port indicated by
   the V4ADDR and PN values.

   [QUESTION: Do we need to optimise hairpinning? ]

   [QUESTION: We want the server to be stateless.  Is there any
   particular defence against DoS using bogus V4ADDR/PN values? ]

4.  Security Considerations

   A basic assumption of SAMPLE is that it is deployed entirely within
   the administrative boundary of a single ISP and its customers.
   SAMPLE-encapsulated packets should never leave or enter that
   administrative boundary.  Threats arising within that boundary need
   to be considered.

   A SAMPLE server SHOULD be configured to discard (with logging if
   required) any incoming SAMPLE packet whose IPv4 source address does
   not belong to any customer of the ISP concerned.  The only exception
   is if [RFC2827] is in use by the ISP.

   [COMMENT: There is work to do here.  It seems intrinsically more
   controlled than either 6to4 or Teredo, since the entire tunnel is
   confined to the ISP's IPv4 realm, but we have to look at the threats
   identified for those two solutions and see which apply here.

   Points to consider: should the user IPv4 address be obfuscated, as in
   Teredo?  Should some random bits be included in the FILL bits, to
   defeat address scanning, as in Teredo? ]

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5.  IANA Considerations

   This document requests no action by IANA.

6.  Acknowledgements

   This document builds on an idea extracted and simplified from

   Valuable comments and contributions were made by ...

   This document was produced using the xml2rfc tool [RFC2629].

7.  Change log

   draft-carpenter-softwire-sample-00: original version, 2010-06-07

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, May 2000.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC4380]  Huitema, C., "Teredo: Tunneling IPv6 over UDP through
              Network Address Translations (NATs)", RFC 4380,
              February 2006.

8.2.  Informative References

              Despres, R., "Stateless Address Mapping (SAM) for
              Softwire-Lite Solutions", draft-despres-softwire-sam-00
              (work in progress), March 2010.

              Carpenter, B. and S. Jiang, "Emerging Service Provider
              Scenarios for IPv6 Deployment",

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              draft-ietf-v6ops-isp-scenarios-00 (work in progress),
              April 2010.

              Lee, Y. and P. Kapoor, "UDP Encapsulation of 6rd",
              draft-lee-softwire-6rd-udp-01 (work in progress),
              May 2010.

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

   [RFC3053]  Durand, A., Fasano, P., Guardini, I., and D. Lento, "IPv6
              Tunnel Broker", RFC 3053, January 2001.

Appendix A.  Main differences from Teredo

   There is a critical difference from Teredo.  The client address in
   Teredo is like this (quoting [RFC4380]):

      | Prefix      | Server IPv4 | Flags | Port | Client IPv4 |

      - Prefix: the 32-bit Teredo service prefix.
      - Server IPv4: the IPv4 address of a Teredo server.
      - Flags: a set of 16 bits that document type of address and NAT.
      - Port: the obfuscated "mapped UDP port" of the Teredo service at
        the client.
      - Client IPv4: the obfuscated "mapped IPv4 address" of the client.

   (end quote)

   Also, in Teredo, the client has to figure out which relay to use:
   "Teredo clients have to discover the relay that is closest to each
   native IPv6 or 6to4 peer.  They have to perform this discovery for
   each native IPv6 or 6to4 peer with which they communicate."

   In the SAMPLE scheme we bind IPv6 routing in both directions to the
   PSAMPLE /64 IPv6 locator; the client sends and receives all its IPv6
   packets to and from the same SAMPLE server's IPv4 address.

   This does introduce a single point of failure and a scaling
   bottleneck, but in exchange we get simplicity and reliability.  We
   don't need Teredo's flag bits; any NAT that supports outbound UDP
   flow initiation will work.

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   The other major difference (and hence simplification) is that we
   assume that any NAT CPE is capable of straightforward port mapping
   for a bidirectional UDP stream, so there is no mechanism for
   detecting what type of NAT is in the way.

   As noted above, the security threats are limited to those that can
   occur inside a single ISP's administrative boundary.

Authors' Addresses

   Brian Carpenter
   Department of Computer Science
   University of Auckland
   PB 92019
   Auckland,   1142
   New Zealand

   Email: brian.e.carpenter@gmail.com

   Sheng Jiang
   Huawei Technologies Co., Ltd
   KuiKe Building, No.9 Xinxi Rd.,
   Shang-Di Information Industry Base, Hai-Dian District, Beijing
   P.R. China

   Email: shengjiang@huawei.com

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