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IPv6 Rapid Deployment on IPv4 Infrastructures (6rd)

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 5569.
Author Rémi Després
Last updated 2020-01-21 (Latest revision 2009-04-07)
RFC stream Independent Submission
Intended RFC status Informational
Stream ISE state (None)
Consensus boilerplate Unknown
Document shepherd (None)
IESG IESG state Became RFC 5569 (Informational)
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Telechat date (None)
Responsible AD Jari Arkko
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Internet Engineering Task Force                               R. Despres
Internet-Draft                                             April 7, 2009
Intended status: Informational
Expires: October 9, 2009

          IPv6 Rapid Deployment on IPv4 infrastructures (6rd)

Status of this Memo

   This Internet-Draft is submitted to IETF 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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   This Internet-Draft will expire on October 9, 2009.

Copyright Notice

   Copyright (c) 2009 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
   Provisions Relating to IETF Documents in effect on the date of
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   Please review these documents carefully, as they describe your rights
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   IPv6 rapid deployment (6rd) builds upon mechanisms of 6to4 (RFC3056)
   to enable a service provider to rapidly deploy IPv6 unicast service
   to IPv4 sites to which it provides customer premise equipment.  Like

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   6to4, it utilizes stateless IPv6 in IPv4 encapsulation in order to
   transit IPv4-only network infrastructure.  Unlike 6to4, a 6rd service
   provider uses an IPv6 prefix of its own in place of the fixed 6to4
   prefix.  A service provider has used this mechanism for its own IPv6
   "rapid deployment": five weeks from first exposure to 6rd principles
   to more than 1,500,000 residential sites being provided native IPv6,
   under the only condition that they activate it.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Problem statement and purpose of 6rd . . . . . . . . . . . . .  5
   3.  Specification  . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Applicability to ISPs that assign private IPv4 addresses . . .  8
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11

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1.  Introduction

   After having had a succinct presentation of the 6rd idea, a major
   French Internet service provider (ISP), Free of the Iliad group, did
   all of the following in an impressively short delay of only five
   weeks (November 7th to December 11th 2007):

   1.  obtain its first IPv6 prefix from its regional Internet Registry
       (RIR), its length being 32 the length that was allocated without
       a justification and a delay to examine it;

   2.  add 6rd support to the software of its Freebox home-gateway
       (upgrading for this an available 6to4 code);

   3.  provision PC-compatible platform with a 6to4 gateway software;

   4.  modify it to support 6rd;

   5.  test IPv6 operation with several operating systems and

   6.  finish operational deployment, by means of new downloadable
       software for Freeboxes;

   7.  announce IPv6 Internet connectivity, at no extra charge, for all
       its customers wishing to activate it.

   More than 1,500,000 residential customers thus became able to use
   IPv6 if they wished to, with all the look and feel of native IPv6
   addresses routed in IPv6.  The only condition was an activation of
   IPv6 in their Freeboxes, and of course in their IPv6 capable hosts.

   This story is reported to illustrate that ISPs that provide customer
   premise equipment to their customers with routing capability (router
   CPEs), and that have so far postponed IPv6 deployment can, with the
   dramatically reduced investment and operational costs that 6rd make
   possible, decide to wait no longer.

   To complete the story, Free announced, on March 6th 2008, that
   provided two of its customer sites had IPv6 activated, its Telesites
   application (Web sites published on TV) could now be used remotely
   between them.

   While IPv6 availability was limited in december 2007 to only one IPv6
   link per customer site (with /64 site prefix assignments), it was
   upgraded a few months later to up to 16 IPv6 links (with /60 site
   prefix assignments), after Free had detailed its achievement and
   plans to its RIR and obtained from it a /26 prefix.

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   Readers are supposed to be familiar with 6to4 [RFC3056].

2.  Problem statement and purpose of 6rd

   Having ISPs to rapidly bring IPv6 to customers sites, in addition to
   IPv4 and without extra charge, is a way to break the existing vicious
   circle that has delayed IPv6 deployment: ISPs wait for customer
   demand before deploying IPv6; customers don't demand IPv6 as long as
   application vendors announce that their products work on existing
   infrastructures (that are IPv4 with NATs); application vendors focus
   their investments on NAT traversal compatibility as long as ISPs
   don't deploy IPv6.

   But most ISPs are not willing to add IPv6 to their current offer, at
   no charge, unless incurred investment and operational costs are
   extremely limited.  For this, ISPs that provide router CPEs to their
   customers have the most favorable conditions: they can upgrade their
   router CPEs to support IPv6 encapsulation and operate gateways
   between these infrastructures and the global IPv6 Internet to also do
   IPv6/v4 encapsulation, so that they can keep the routing plan of
   their IPv4 infrastructures.

   Encapsulation a la 6to4 is very close to be sufficient for this: it
   is simple; it is supported on many platforms including PC compatible
   appliances; open-source portable code is available; its stateless
   nature ensures good scalability.

   There is however a limitation of 6to4 that prevents ISPs to use it to
   offer full IPv6 unicast connectivity to their customers.  While an
   ISP that deploys 6to4 can guarantee that IPv6 packets outgoing from
   its customer sites will reach the IPv6 Internet, and also guarantee
   that packets coming from other 6to4 sites will reach its customer
   sites, it cannot guarantee that packets from native IPv6 sites will
   reach them.  A packet coming from a native IPv6 address needs to
   traverse, somewhere on its way, a 6to4 relay router do the required
   IPv6/IPv4 encapsuation.  The problem is that there is no guarantee to
   have a route toward such a relay from everywhere, nor is there a
   guarantee that all such relays do forward packets toward the complete
   IPv4 Internet.

   An ISP, if it operates one or several 6to4 relay routers and opens
   IPv6 routes toward them on the IPv6 Internet for the 6to4 prefix
   2002::/16, may receive in these relays packets destined to an unknown
   number of other 6to4 ISPs.  If it doesn't forward them, it creates a
   black hole in which packets may be systematically lost, breaking some
   of the IPv6 connectivity.  If it does forward them, it can no longer
   dimension its 6to4 relay routers in proportion to the traffic of its

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   own customers.  Quality of service, at least for customers of other
   6to4 ISPs, will then hardly be guaranteed.

   The purpose of 6rd is to slightly modify 6to4 so that:

   1.  Packets that, coming from the global Internet, enter 6rd gateways
       of an ISP are only packets destined to customer sites of this

   2.  All IPv6 packets destined to 6rd customer sites of an ISP, and
       coming from anywhere else on the IPv6 Internet, traverse a 6rd
       gateway of this ISP.

3.  Specification

   The principle of 6rd is that, to build on 6to4 and suppress its
   limitation, it is sufficient that:

   1.  6to4 functions are modified to replace the standard prefix
       2002::/16 by an IPv6 prefix that belongs to the ISP assigned
       address space, and to replace the 6to4 anycast address by another
       anycast address chosen by the ISP.

   2.  The ISP operates one or several 6rd gateways (upgraded 6to4
       routers) at its border between its IPv4 infrastructure and the
       IPv6 Internet.

   3.  CPE routers are IPv6 on their customer-site side and support 6rd
       (upgraded 6to4 function).

   Figure 1 shows how the IPv6 prefix of a customer site is derived from
   its IPv4 address.

               | 6rd-relays IPv6 prefix |         IPv4 address         |
               |        of the ISP      |     of the customer site     |
               <-- less or equal to 32 -><------------ 32 ------------->
               <-- less or equal to  64 ------------------------------->


                                 Figure 1

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   The chosen address format uses 32 bits of IPv4 address within the
   IPv6 address for reasons of simplicity and of compatibility with the
   existing 6to4 code.  Free's customers being essentially residential,
   limiting initially their sites to one IPv6 subnet per site was not a
   significant restriction: most of them would not have been able to use
   several subnets anyway; as soon as Free would get shorter a prefix
   than /32, this restriction could be relaxed.

          IPv4 AND IPv6 customer site
          |   6rd CPEs                         6rd relays
          | (modified 6to4)                  (modified 6to4)
          |     |                                   |
          |     |    __________________________     |
          |     |   |                          |    |
          |     |   | ISP IPV4 INFRASTRUCTURE  |    V    GLOBAL
          V     V   |                          |   ___    IPV6
              ___   |                          |  |   | INTERNET
          |  |   |  |        .-----------------|--|   |---
          |--|   |--|-.     /                  |  |___|
          |  |___|  |  \   /                   |
                    |   \ /      IPv4          |      IPv6 Prefix
                    |    O  anycast address => |  <= of 6rd relays
          |   ___   |   / \  of 6rd relays     |      of the ISP
          |  |   |  |  /   \                   |   ___
          |--|   |--|-'     \                  |  |   |
          |  |___|  |        '-----------------|--|   |---
          |         |                          |  |___|
                    |      IPv4 addresses      |
                    | <= of customer sites     |


                                 Figure 2

   NOTE: If it had been important to use less than 32 bits of IPv4
   addresses in IPv6 prefixes, this would have been possible.  Since
   Free, like many ISPs, had several RIR allocated IPv4 prefixes (6 of
   them, having lengths from /10 to /16 in the particular case), 6rd
   gateways and 6rd CPEs would however have had for this to support a
   variable length mapping table.  Some of the IPv4 addressing entropy
   would thus have been extended to 6rd gateways and CPEs, and
   complexity would have been significantly higher.  This would have
   defeated the objective of extreme simplicity to favor actual and
   rapid deployment.

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   Figure 2 shows which nodes have to be upgraded from 6to4 to 6rd, and
   which addresses or prefixes have to be routed to them.

   IPv6 communication between customer sites of a same ISP is direct
   across the ISP IPv4 infrastructure: when a CPE sees that the IPv6
   destination address of an outgoing packet starts with its own 6rd
   relay ISPv6 prefix, it takes the 32 bits that follow this prefix as
   IPv4 destination of the encapsulating packet.  (Sending and
   decapsulation rules of 6to4, duly adapted to the 6rd prefix in place
   of the 6to4 prefix, apply as described in [RFC3056] section 5.3.)

   The IPv4 anycast address of 6rd relays may be chosen independently by
   each ISP.  The only constraint is that routes toward the ISP that are
   advertised must not include this address.  For example, Free took a
   192.88.99.k address, routed with the same /24 prefix as 6to4 but with
   k different from 1 to avoid confusion with the 6to4 address of
   [RFC3068].  Another possibility is to use the anycast address of 6to4
   and to add, in relays, a test on the IPv6 prefix of the ISP side
   address.  If it is 2002::/16, the packet is 6to4, not 6rd.

4.  Applicability to ISPs that assign private IPv4 addresses

                    |                              |
                    | 10.x.x.x/8 private addresses |
                    |  <==                         |
              <-----|         IPv4 Anycast address |----->
                    |            of 6rd relays     |
           6rd-CPEs |                      ==>     |  6rd-relays
                    |                              |
              <-----|           |----->
                    |              :               |
           ISP-supported NAT(s) |     |
                        IPv4 public addresses


                                 Figure 3

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   If an ISP has assigned to customer sites addresses of an IPv4 private
   space of [RFC1918], typically 10.x.x.x/8 addresses, it can also use
   6rd to offer IPv6 to these sites.

   IPv4 packets that contain IPv6 packets don't go to NATs which this
   ISP needs to operate in its infrastructure: they go directly to 6rd
   relays because their destination is the 6rd relay anycast address.

   Note that in this case the prefix is common to all IPv4
   addresses of the addressing realm in which 6rd is used.  Knowing it,
   gateways and CPE can avoid including this constant IPv4 prefix in
   IPv6 prefixes, and thus reduce to 24 the number of bits of IPv4
   addresses to be used in IPv6 prefixes.

   If an ISP is large enough to provide service to more IPv4 endpoints
   than will fit inside a 10.x.x.x/8 addressing realm, it can configure
   several such realms, with 6rd-relay IPv6 prefixes specific of each
   one.  Each of these prefixes is the RIR allocated ISP prefix followed
   by an ISP assigned realm identifier.

5.  Security Considerations

   Security considerations for 6to4 are documented in [RFC3964].  With
   the restriction imposed by 6rd that relays of an ISP deal only with
   traffic that belongs to that ISP, checks that have to be done become
   the following:

   o  CPE PACKETS TOWARD THE INTERNET: The IPv6 source must be, and the
      IPv6 destination must no be, a 6rd address of the site.

   o  RELAY PACKETS TOWARD THE INTERNET: The IPv6 source must be a 6rd
      address that matches the IPv4 source.  The IPv6 destination must
      not start with the ISP 6rd prefix.

   o  CPE PACKETS FROM THE INTERNET: If the IPv4 source is the 6rd-
      relays anycast address of the local ISP, the IPv6 source must not
      be a 6rd address of this ISP.  Otherwise, the IPv6 source must be
      the 6rd address that matches the IPv4 source.

   o  RELAY PACKETS FROM THE INTERNET: The IPv6 source must not be a 6rd
      address of the ISP.  The IPv4 destination must not be multicast,
      i.e. must not start with 224/3.  (Notes: The fact that the IPv6
      destination starts with the IPv6 prefix of the ISP 6rd relays is
      ensured by the routing configuration, but may be double-checked.
      If the IPv4 address extracted from the IPv6 destination doesn't
      belong to the ISP, the destination CPE should detect that the IPv6
      destination contains neither its ISP 6rd prefix, if it has one,

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      nor the 6to4 prefix, and should discard the packet.)

   These precautions being taken, it remains that, where IPv4 address
   spoofing is possible (IPv4 sites placing unauthorized source
   addresses in some packets they send), IPv6 address spoofing is also

6.  IANA Considerations

   ISPs that provide CPEs to all their customers need no new number
   assignment by IANA.  Their being allocated an IPv6 prefix by their
   RIR, /32 or shorter, is sufficient.

   For 6rd to be also used by ISPs that let customers have their own
   CPEs, means to communicate 6rd parameters to these CPEs are needed.
   For this, IANA has to eventually be involved."

7.  Acknowledgements

   The author warmly acknowledges the major contribution of Rani Assaf
   to 6rd's proven credibility.  He readily appreciated 6rd's potential,
   and made the daring decision to rapidly implement it and deploy it on
   Free's operational network.  Mark Townsley, Brian Carpenter and
   Patrick Grossetete have to be thanked for their encouragements and
   suggestions as to how to proceed in IETF.

   Acknowledgments are also due to some IPv6 old timers, in particular
   Laurent Toutain, Francis Dupont and Alain Durand, who, when the
   author came as a late novice on IPV6, taught him a few subtleties of
   the subject.  Without them, designing 6rd would probably not have
   been possible.

8.  References

8.1.  Normative References

   [RFC3056]  Carpenter, B. and K. Moore, "Connection of IPv6 Domains
              via IPv4 Clouds", RFC 3056, February 2001.

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

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8.2.  Informative References

   [IPv4 addresses]
              Internet Assigned Numbers Authority, "Internet Protocol v4
              Address Space -
              February 2008.

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

   [RFC3068]  Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
              RFC 3068, June 2001.

   [RFC3964]  Savola, P. and C. Patel, "Security Considerations for
              6to4", RFC 3964, December 2004.

Author's Address

   Remi Despres
   3 rue du President Wilson

   Phone: +33 6 72 74 94 88

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