v6ops                                                  V. Kuarsingh, Ed.
Internet-Draft                                     Rogers Communications
Intended status: Informational                                    Y. Lee
Expires: January 11, 2013                                        Comcast
                                                              O. Vautrin
                                                        Juniper Networks
                                                           July 10, 2012

                     6to4 Provider Managed Tunnels


   6to4 Provider Managed Tunnels (6to4-PMT) provide a framework which
   can help manage 6to4 tunnels operating in an anycast configuration.
   The 6to4-PMT framework is intended to serve as an option for
   operators to help improve the experience of 6to4 operation when
   conditions of the network may provide sub-optimal performance or
   break normal 6to4 operation. 6to4-PMT provides a stable provider
   prefix and forwarding environment by utilizing existing 6to4 relays
   with an added function of IPv6 Prefix Translation.  This operation
   may be particularly important in NAT444 infrastructures where a
   customer endpoint may be assigned a non-RFC1918 address thus breaking
   the return path for anycast based 6to4 operation. 6to4-PMT has
   successfully been used in a production network, has been implemented
   as open source code, and implemented by a major routing vendor.

Status of this Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on January 11, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   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.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  6to4 Provider Managed Tunnels  . . . . . . . . . . . . . . . .  5
     3.1.  6to4 Provider Managed Tunnel Model . . . . . . . . . . . .  5
     3.2.  Traffic Flow . . . . . . . . . . . . . . . . . . . . . . .  5
     3.3.  Prefix Translation . . . . . . . . . . . . . . . . . . . .  6
     3.4.  Translation State  . . . . . . . . . . . . . . . . . . . .  7
   4.  Deployment Considerations and Requirements . . . . . . . . . .  7
     4.1.  Customer Opt-out . . . . . . . . . . . . . . . . . . . . .  7
     4.2.  Shared CGN Space Considerations  . . . . . . . . . . . . .  8
     4.3.  End to End Transparency  . . . . . . . . . . . . . . . . .  8
     4.4.  Path MTU Discovery Considerations  . . . . . . . . . . . .  9
     4.5.  Checksum Management  . . . . . . . . . . . . . . . . . . .  9
     4.6.  Application Layer Gateways . . . . . . . . . . . . . . . .  9
     4.7.  Routing Requirements . . . . . . . . . . . . . . . . . . .  9
     4.8.  Relay Deployments  . . . . . . . . . . . . . . . . . . . . 10
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12

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1.  Introduction

   6to4 [RFC3056] tunnelling along with the anycast operation described
   in [RFC3068] is widely deployed in modern Operating Systems and off
   the shelf gateways sold throughout the retail and OEM channels.
   Anycast [RFC3068] based 6to4 allows for tunnelled IPv6 connectivity
   through IPv4 clouds without explicit configuration of a relay
   address.  Since the overall system utilizes anycast forwarding in
   both directions, flow paths are difficult to determine, tend to
   follow separate paths in either direction, and often change based on
   network conditions.  The return path is normally uncontrolled by the
   local operator and can contribute to poor performance for IPv6, and
   can also act as a breakage point.  Many of the challenges with 6to4
   are described in [RFC6343].  A specific critical use case for
   problematic anycast 6to4 operation is related to conditions where the
   consumer endpoints are downstream from a northbound CGN [RFC6264]
   function when assigned non-RFC1918 IPv4 addresses, which are not
   routed on interdomain links.

   Operators which are actively deploying IPv6 networks and operate
   legacy IPv4 access environments may want to utilize the existing 6to4
   behaviour in customer site resident hardware and software as an
   interim option to reach the IPv6 Internet in advance of being able to
   offer full native IPv6.  Operators may also need to address the
   brokenness related to 6to4 operation originating from behind a
   provider NAT function. 6to4-PMT offers an operator the opportunity to
   utilize IPv6 Prefix Translation to enable deterministic traffic flow
   and an unbroken path to and from the Internet for IPv6 based traffic
   sourced originally from these 6to4 customer endpoints.

   6to4-PMT translates the prefix portion of the IPv6 address from the
   6to4 generated prefix to a provider assigned prefix which is used to
   represent the source.  This translation will then provide a stable
   forward and return path for the 6to4 traffic by allowing the existing
   IPv6 routing and policy environment to control the traffic. 6to4-PMT
   is primarily intended to be used in a stateless manner to maintain
   many of the elements inherent in normal 6to4 operation.
   Alternatively, 6to4-PMT can be used in a stateful translation mode
   should the operator choose this option.

2.  Motivation

   Many operators endeavour to deploy IPv6 as soon as possible so as to
   ensure uninterrupted connectivity to all Internet applications and
   content through the IPv4 to IPv6 transition process.  The IPv6
   preparations within these organizations are often faced with both
   financial challenges and timing issues related to deploying IPv6 to

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   the network edge and related transition technologies.  Many of the
   new technologies available for IPv4 to IPv6 transition will require
   the replacement of the customer CPE to support technologies like 6RD
   [RFC5969], Dual-Stack Lite [RFC6333] and Native Dual Stack.

   Operators face a number of challenges related to home equipment
   replacement.  Operator initiated replacement of this equipment will
   take time due to the nature of mass equipment refresh programs or may
   require the consumer to replace their own gear.  Replacing consumer
   owned and operated equipment, compounded by the fact that there is
   also a general unawareness of what IPv6 is, also adds to the
   challenges faced by operators.  It is also important to note that
   6to4 is found in much of the equipment found in networks today which
   do not as of yet, or will not, support 6RD and/or Native IPv6.

   Operators may still be motivated to provide a form of IPv6
   connectivity to customers and would want to mitigate potential issues
   related to IPv6-only deployments elsewhere on the Internet.
   Operators also need to mitigate issues related to the fact that 6to4
   operation often is on by default and may be subject to erroneous
   behaviour.  The undesired behaviour may be related to the use of non-
   RFC1918 addresses on CPE equipment which operate behind large
   operator NATs, or other conditions as described in a general advisory
   as laid out in [RFC6343].

   6to4-PMT allows an operator to help mitigate such challenges by
   leveraging the existing 6to4 deployment base, while maintaining
   operator control of access to the IPv6 Internet.  It is intended for
   use when better options, such as 6RD or Native IPv6, are not yet
   viable.  One of key objectives of 6to4-PMT is to also help reverse
   the negative impacts of 6to4 in CGN environments.  The 6to4-PMT
   operation can also be used immediately with the default parameters
   which are often enough to allow it to operate in a 6to4-PMT
   environment.  Once native IPv6 is available to the endpoint, the
   6to4-PMT operation is no longer needed and will cease to be used
   based on correct address selection behaviours in end hosts [RFC3484].

   6to4-PMT thus helps operators remove the impact of 6to4 in CGN
   environments, deals with the fact that 6to4 is often on by default,
   allows access to IPv6-only endpoints from IPv4-only addressed
   equipment and provides relief from many challenges related to mis-
   configurations in other networks which control return flows via
   foreign relays.  Due to the simple nature of 6to4-PMT, it can also be
   implemented in a cost effective and simple manner allowing operators
   to concentrate their energy on deploying Native IPv6.

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3.  6to4 Provider Managed Tunnels

3.1.  6to4 Provider Managed Tunnel Model

   The 6to4 managed tunnel model behaves like a standard 6to4 service
   between the customer IPv6 host or gateway and the 6to4-PMT Relay
   (within the provider domain).  The 6to4-PMT Relay shares properties
   with 6RD [RFC5969] by decapsulating and forwarding encapsulated IPv6
   flows within an IPv4 packet, to the IPv6 Internet.  The model
   provides an additional function which translates the source 6to4
   prefix to a provider assigned prefix which is not found in 6RD
   [RFC5969] or traditional 6to4 operation.

   The 6to4-PMT Relay is intended to provide a stateless (or stateful)
   mapping of the 6to4 prefix to a provider supplied prefix.

                             | 6to4-PMT Operation  |

          +-----+ 6to4 Tunnel +--------+  +------+  IPv6    +----+
          | CPE |-------------|6to4 BR |--| PT66 |--------- |Host|
          +-----+    IPv4     +--------+  +------+ Provider +----+
                    Network                         Prefix
                               Unified or Separate

                    Figure 1: 6to4-PMT Functional Model

   This mode of operation is seen as beneficial when compared to broken
   6to4 paths and/or environments where 6to4 operation may be functional
   but highly degraded.

3.2.  Traffic Flow

   Traffic in the 6to4-PMT model is intended to be controlled by the
   operator's IPv6 peering operations.  Egress traffic is managed
   through outgoing routing policy, and incoming traffic is influenced
   by the operator assigned prefix advertisements using normal
   interdormain routing functions.

   The routing model is as predictable as native IPv6 traffic and legacy
   IPv4 based traffic.  Figure 2 provides a view of the routing topology
   needed to support this relay environment.  The diagram references
   PrefixA as 2002::/16 and PrefixB as the example 2001:db8::/32.

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        |  6to4 IPv4 Path     |       Native IPv6 Path            |
               -----------       -----------      -------------
              /  IPv4 Net \     /  IPv6 Net  \  / IPv6 Internet \
        +------+         +--------+         +-------+    +---------+
        | CPE  | PrefixA |6to4-PMT| PrefixB |Peering|    |IPv6 HOST|
        +------+         +--------+         +-------+    +---------+
              \           /     \            /  \               /
               ----------        ------------     --------------

                IPv4 6to4       IPv6 Provider       IPv6 Prefix
                 Anycast           Prefix           Propagation

                       Figure 2: 6to4-PMT Flow Model

   Traffic between two 6to4 enabled devices would use the IPv4 path for
   communication according to RFC3056 unless the local host still
   prefers traffic via a relay. 6to4-PMT is intended to be deployed in
   conjunction with the 6to4 relay function in an attempt to help
   simplify it's deployment.  The model can also provide the ability for
   an operator to forward both 6to4-PMT (translated) and normal 6to4
   flows (untranslated) simultaneously based on configured policy.

3.3.  Prefix Translation

   IPv6 Prefix Translation is a key part of the system as a whole.  The
   6to4-PMT framework is a combination of two concepts: 6to4 [RFC3056]
   and IPv6 Prefix Translation.  IPv6 Prefix Translation, as used in
   6to4-PMT, has some similarities to concepts discussed in [RFC6296].
   6to4-PMT would provide prefix translation based on specific rules
   configured on the translator which maps the 6to4 2002::/16 prefix to
   an appropriate provider assigned prefix.  In most cases, a ::/32
   prefix would work best in 6to4-PMT which matches common RIR prefix
   assignments to operators.

   The provider can use any prefix mapping strategy they so choose, but
   the simpler the better.  Simple direct bit mapping can be used, or
   more advanced forms of translation should the operator want to
   achieve higher address compression.  More advanced forms of
   translation may require the use of stateful translation.

   Figure 3 shows a 6to4 Prefix with a Subnet-ID of "0000" mapped to a
   provider assigned globally unique prefix (2001:db8::/32).  With this
   simple form of translation, there is support for only one Subnet-ID
   per provider assigned prefix.  In characterization of deployed OSs
   and gateways, a Subnet-ID of "0000" is the most common default case
   followed by Subnet-ID "0001".  Use of Subnet-ID can be referenced in
   [RFC4291].  It should be noted that in normal 6to4 operation the
   endpoint (network) has access to 65,536 (16-bits) Subnet IDs.  In the

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   6to4-PMT case as described above using the mapping in Figure 3, all
   but the one Subnet-ID used for 6to4-PMT would still operate under
   normal 6to4 operation.

      Pre-Relayed Packet [Provider Access Network Side]

      0     16      32     48     64    80     96     112    128 Bits
      | ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- |
        2002 : 0C98 : 2C01 : 0000 : xxxx : xxxx : xxxx : xxxx
      | ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- |
                 |       |            |      |      |      |
                  ----    ----        |      |      |      |
                      |       |       |      |      |      |
      | ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- |
        2001 : 0db8 : 0c98 : 2c01 : xxxx : xxxx : xxxx : xxxx
      | ---- | ---- | ---- | ---- | ---- | ---- | ---- | ---- |

      Post-Relayed Packet [Internet Side]

                     Figure 3: 6to4-PMT Prefix Mapping

3.4.  Translation State

   It is preferred that the overall system use deterministic prefix
   translation mappings such that stateless operation can be
   implemented.  This allows the provider to place N number of relays
   within the network without the need to manage translation state.
   Deterministic translation also allows a customer to use inward
   services using the translated (provider prefix) address.

   If stateful operation is chosen, the operator would need to validate
   state and routing requirements particular to that type of deployment.
   The full body of considerations for this type of deployment are not
   within this scope of this document.

4.  Deployment Considerations and Requirements

4.1.  Customer Opt-out

   A provider enabling this function should provide a method to allow
   customers to opt-out of such a service should the customer choose to
   maintain normal 6to4 operation irrespective of degraded performance.
   In cases where the customer is behind a CGN device, the customer
   would not be advised to opt-out and can also be assisted to turn off

   Since the 6to4-PMT system is targeted at customers who are relatively

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   unaware of IPv6 and IPv4, and normally run network equipment with a
   default configuration, an opt-out strategy is recommended.  This
   method provides 6to4-PMT operation for non-IPv6 savvy customers whose
   equipment may turn on 6to4 automatically and allows savvy customers
   to easily configure their way around the 6to4-PMT function.

   Capable customers can also disable anycast based 6to4 entirely and
   use traditional 6to4 or other tunnelling mechanisms if they are so
   inclined.  This is not considered the normal case, and most endpoints
   with auto-6to4 functions will be subject to 6to4-PMT operation since
   most users are unaware of it's existence. 6to4-PMT is targeted as an
   option for stable IPv6 connectivity for average consumers.

4.2.  Shared CGN Space Considerations

   6to4-PMT operation can also be used to mitigate a known problem with
   6to4 when shared address space [RFC6598] or Global Unicast Addresses
   (GUA) are used behind a CGN and not routed on the Internet.  Non-
   RFC1918, yet un-routed (on interdomain links) address space would
   cause many deployed OSs and network equipment to potentially auto-
   enable 6to4 operation even without a valid return path (such as
   behind a CGN function).  The Operators' desire to use non-RFC1918
   addresses, such as shared address space [RFC6598], is considered
   highly likely based on real world deployments.

   Such hosts, in normal cases, would send 6to4 traffic to the IPv6
   Internet via the anycast relay, which would in fact provide broken
   IPv6 connectivity since the return path flow is built using an IPv4
   address that is not routed or assigned to the source Network.  The
   use of 6to4-PMT would help reverse these effects by translating the
   6to4 prefix to a provider assigned prefix, masking this automatic and
   undesired behaviour.

4.3.  End to End Transparency

   6to4-PMT mode operation removes the traditional end to end
   transparency of 6to4.  Remote hosts would connect to a 6to4-PMT
   serviced host using a translated IPv6 address versus the original
   6to4 address based on the 2002::/16 well-known prefix.  This can be
   seen as a disadvantage of the 6to4-PMT system.  This lack of
   transparency should also be contrasted with the normal operating
   state of 6to4 which provides uncontrolled and often high latency
   prone connectivity.  The lack of transparency is however a better
   form of operation when extreme poor performance, broken IPv6
   connectivity, or no IPv6 connectivity is considered as the

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4.4.  Path MTU Discovery Considerations

   The MTU will be subject to a reduced value due to standard 6to4
   tunnelling operation.  Under normal 6to4 operation, the 6to4 service
   agent would send an ICMP Packet Too Big Message as part of Path MTU
   Discovery as described in [RFC4443] and [RFC1981] respectively.  In
   6to4-PMT operation, the PMT Service agent should be aware of the
   reduced 6to4 MTU and send ICMP messages using the translated address

   It is also possible to pre-constrain the MTU at the upstream router
   from the 6to4-PMT service agents which would then have the upstream
   router send the appropriate ICMP Packet Too Big Messages.

4.5.  Checksum Management

   Checksum management for 6to4-PMT can be implemented in one of two
   ways.  The first deployment model is based on the stateless 6to4-PMT
   operational mode.  In this case, checksum modifications are made
   using the method described in [RFC3022] section 4.2.  The checksum is
   modified to match the parameters of the translated address of the
   source 6to4-PMT host.  In the second deployment model where stateful
   6to4-PMT translation is used, the vendor can implement checksum
   neutral mappings as defined in [RFC6296].

4.6.  Application Layer Gateways

   Vendors can choose to deploy ALGs on their platforms that perform
   6to4-PMT if they so choose.  No ALGs were deployed as part of the
   open source and vendor product deployments of 6to4-PMT.  In the
   vendor deployment case, the same rules were used as with their NPTv6
   [RFC6296] base code.

4.7.  Routing Requirements

   The provider would need to advertise the well-known IP address range
   used for normal anycast 6to4 [RFC3068] operation within the local
   IPv4 routing environment.  This advertisement would attract the 6to4
   upstream traffic to a local relay.  To control this environment and
   make sure all northbound traffic lands on a provider controlled
   relay, the operator may filter the anycast range from being
   advertised from customer endpoints toward the local network (upstream

   The provider would not be able to control route advertisements inside
   the customer domain, but that use case is not in scope for this
   document.  It is likely in that case the end network/customer
   understands 6to4 and is maintaining their own relay environment and

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   therefore would not be subject to the operators 6to4 and/or PMT

   The provider would also likely want to advertise the 2002::/16 range
   within their own network to help bridge traditional 6to4 traffic
   within their own network (Native IPv6 to 6to4-PMT based endpoint).
   It would also be advised that the local 6to4-PMT operator not leak
   the well-known 6to4 anycast IPv4 prefix to neighbouring Autonomous
   Systems to prevent PMT operation for neighbouring networks.  Policy
   configuration on the local 6to4-PMT relay can also be used to
   disallow PMT operation should the local provider service downstream
   customer networks.

4.8.  Relay Deployments

   The 6to4-PMT function can be deployed onto existing 6to4 relays (if
   desired) to help minimize network complexity and cost. 6to4-PMT has
   already been developed on Linux based platforms which are package
   add-ons to the traditional 6to4 code.  The only additional
   considerations beyond normal 6to4 relay operation would include the
   need to route specific IPv6 provider prefix ranges used for 6to4-PMT
   operation towards peers and transit providers.

5.  IANA Considerations

   No IANA considerations are defined at this time.

6.  Security Considerations

   6to4-PMT operation would be subject to the same security concerns as
   normal 6to4 operation. 6to4-PMT is also not plainly perceptible by
   external hosts and local entities appear as Native IPv6 hosts to the
   external hosts.

7.  Acknowledgements

   Thanks to the following people for their textual contributions and/or
   guidance on 6to4 deployment considerations: Dan Wing, Wes George,
   Scott Beuker, JF Tremblay, John Brzozowski, Chris Metz and Chris

   Additional thanks to the following for assisting with the coding and
   testing of 6to4-PMT: Marc Blanchet, John Cianfarani, Tom Jefferd, Nik
   Lavorato, Robert Hutcheon and Ida Leung

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8.  References

8.1.  Normative References

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

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

8.2.  Informative References

   [RFC1981]  McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
              for IP version 6", RFC 1981, August 1996.

   [RFC3022]  Srisuresh, P. and K. Egevang, "Traditional IP Network
              Address Translator (Traditional NAT)", RFC 3022,
              January 2001.

   [RFC3484]  Draves, R., "Default Address Selection for Internet
              Protocol version 6 (IPv6)", RFC 3484, February 2003.

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

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

   [RFC5969]  Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
              Infrastructures (6rd) -- Protocol Specification",
              RFC 5969, August 2010.

   [RFC6264]  Jiang, S., Guo, D., and B. Carpenter, "An Incremental
              Carrier-Grade NAT (CGN) for IPv6 Transition", RFC 6264,
              June 2011.

   [RFC6296]  Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
              Translation", RFC 6296, June 2011.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.

   [RFC6343]  Carpenter, B., "Advisory Guidelines for 6to4 Deployment",
              RFC 6343, August 2011.

   [RFC6598]  Weil, J., Kuarsingh, V., Donley, C., Liljenstolpe, C., and

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              M. Azinger, "IANA-Reserved IPv4 Prefix for Shared Address
              Space", BCP 153, RFC 6598, April 2012.

Authors' Addresses

   Victor Kuarsingh (editor)
   Rogers Communications
   8200 Dixie Road
   Brampton, Ontario  L6T 0C1

   Email: victor.kuarsingh@gmail.com
   URI:   http://www.rogers.com

   Yiu L. Lee
   One Comcast Center
   Philadelphia, PA  19103

   Email: yiu_lee@cable.comcast.com
   URI:   http://www.comcast.com

   Olivier Vautrin
   Juniper Networks
   1194 N Mathilda Avenue
   Sunnyvale, CA  94089

   Email: olivier@juniper.net
   URI:   http://www.juniper.net

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