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Versions: 00 01                                                         
Internet Engineering Task Force                                A. Durand
Internet-Draft                                                   Comcast
Intended status: Informational                         November 12, 2007
Expires: May 15, 2008


        Non dual-stack IPv6 deployments for broadband providers
                    draft-durand-v6ops-natv4v6v4-00

Status of this Memo

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   This Internet-Draft will expire on May 15, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   The common thinking for the last 10+ years has been to say that dual
   stack was the answer to v6 transition and that most things would be
   converted to dual stack way before we ran out of v4.  Well, it has
   not happened.  We are going to run out of IPv4 addresses soon, way
   before any significant IPv6 deployment will have occur.  As a result,
   broadband deployments now need to contemplate IPv6-only provisioning
   and NAT as a classic solution to maintain some form of connectivity
   between those environments and the legacy Internet.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . . . 3
   2.  IPv4 exhaustion coming sooner than expected . . . . . . . . . . 3
   3.  Handling the legacy . . . . . . . . . . . . . . . . . . . . . . 3
     3.1.  Legacy edges of the Internet for broadband customers  . . . 3
     3.2.  Content and Services available on the Internet  . . . . . . 4
     3.3.  Burden on service providers . . . . . . . . . . . . . . . . 4
   4.  Solution space  . . . . . . . . . . . . . . . . . . . . . . . . 4
     4.1.  IPv6-only . . . . . . . . . . . . . . . . . . . . . . . . . 4
     4.2.  Double IPv4->IPv4->IPv4 NAT . . . . . . . . . . . . . . . . 4
     4.3.  Double IPv4->IPv6->IPv4 NAT . . . . . . . . . . . . . . . . 5
     4.4.  Tunneling . . . . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6
   Intellectual Property and Copyright Statements  . . . . . . . . . . 7































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1.  Introduction

   This memo will present a service provider view on IPv6 deployment and
   some of the necessary technologies to achieve it.

1.1.  Requirements Language

   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 [RFC2119].


2.  IPv4 exhaustion coming sooner than expected

   Global public IPv4 addresses coming from the IANA free pool are
   running out faster than predicted a few years ago.  The current model
   shows that exhaustion could happen as early as 2010.  See
   http://ipv4.potaroo.net for more details.  Those projection ares
   based on the assumption that tomorrow is going to be very similar to
   today, ie looking at recent address consumption figures is a good
   indicator of future consumption patterns.  This of course, does not
   take into account any new large scale deployment of IP technology or
   any human reaction when facing an upcoming shortage.

   The prediction of the exact date of exhaustion of the IANA free pool
   is outside the scope of this document, however one conclusion must be
   drawn from that study: there will be in the near future a point where
   new global public IPv4 addresses will not be available and thus any
   new broadband deployment may have to consider the option of not
   provisioning any IPv4 addresses to the WAN facing interface of edge
   devices.  The IPv6 deployment model known as "dual stack" can be a
   non starter in such environments.


3.  Handling the legacy

3.1.  Legacy edges of the Internet for broadband customers

   Broadband customers have a mix and match of IP enable devices at
   home.  The most recent operating systems (eg Windows Vista or
   MacOS-X) can operate in an IPv6-only environment, however most of the
   legacy one can't.  It has been reported, for example, that windows XP
   cannot process DNS requests over IPv6 transport.  Expecting broadband
   customers to massively upgrade their software (and in most cases the
   corresponding hardware) to deploy IPv6 is a very tall order.






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3.2.  Content and Services available on the Internet

   IPv6 deployment has been very long to take off, so the current
   situation is that almost none of the content and services available
   on the Internet are accessible over IPv6.  This will probably change
   in the future, but for now, one has to make the assumption that most
   of the traffic generated by (and to) broadband customers will be sent
   to (and originated by) IPv4 nodes.

3.3.  Burden on service providers

   As a conclusion, broadband service providers may be faced with the
   situation where they have IPv4 customers willing to communicate with
   IPv4 servers on the Internet but may not have any IPv4 addresses left
   to assign to them...


4.  Solution space

   A number of solution can be studied in that space: IPv6-only, double
   IPv4>IPv4->IPv4 NAT, double IPv4->IPv6->IPv4 NAT, and IPv4 over IPv6
   tunneling.

4.1.  IPv6-only

   The first solution that comes to mind is simply to provision new
   broadband customers with only IPv6 addresses.  However, two immediate
   issues come to mind:

   a.  Legacy devices in the customer home will not be able to
       communicate with the outside.

   b.  New IPv6-only capable devices will not be able to communicate
       with legacy IPv4-only servers in the Internet.

4.2.  Double IPv4->IPv4->IPv4 NAT

   This solution consists of provisioning broadband customers with a
   private [RFC1918] address on the WAN side of the home gateway, and
   then translate this private IPv4 address somewhere within the service
   provider network into a global IPv4 address.  Devices behind the home
   gateway will then be translated twice, once by the home gateway
   itself, and another time by the NAT within the service provider.

   This solution has the advantage of reducing the total number of
   global IPv4 addresses needed by consolidating the traffic of multiple
   customers on a unique IPv4 addresses.  The first drawback is that
   some applications may have a more difficult time going through two



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   levels of NAT.  Another drawback that can be a show stopper is that
   this solution limits the number of customer within an access network
   to the size of net 10, ie somewhere between 10 and 16 million
   depending on address efficiency.  Note that very large networks such
   as Comcast have already ran out of RFC1918 space a few years ago.

4.3.  Double IPv4->IPv6->IPv4 NAT

   When private address space is running out as well, the next step is
   to have the home gateway translate internal RFC1918 space into global
   IPv6 addresses.  However, as the final destination may not be
   configured with IPv6, those packets will have to be translated a
   second time into IPv4 packets.  This second translation will have to
   occur within the service provider network.

   The implications of this second level of translation is very similar
   to those in the model above of a double IPv4->IPv4->IPv4 translation.
   There will be a need for a far of translator within the service
   provider network operating at line speed.  Some applications may have
   a harder time working through a second level of NAT.  On top of that,
   some MTU adaptation will have to take place to accommodate for the
   longer IPv6 header.

4.4.  Tunneling

   When IPv6-only connectivity is offered to the customer, one could be
   tempted to look at IPv4 over IPv6 tunnels to re-establish
   connectivity for the legacy IPv4 hosts.  The Softwire hub and spoke
   solution, based on L2TP tunnels could be the perfect candidate in
   that space.

   However, the main drawback of that solution is that it would require
   an IPv4 address to be configured on that tunnel.  More, that address
   could not be shared among subscribers.  As such, this solution would
   not consume less IPv4 addresses than a regular dual-stack deployment
   and will be be a non starter in environment where IPv4 addresses are
   rare.


5.  Acknowledgements

   Send the author comments if you want your name listed here.


6.  IANA Considerations

   This memo includes no request to IANA.




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   This draft does not request any IANA action.


7.  Security Considerations

   Security issues associated with NAT have long been documented.  A
   future version of this document may include some references here to
   previous work.


8.  Normative References

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


Author's Address

   Alain Durand
   Comcast
   1500 Market st
   Philadelphia, PA  19102
   USA

   Email: alain_durand@cable.comcast.com


























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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

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