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Independent Submission                                 V. Kuarsingh, Ed.Request for Comments: 6732                         Rogers CommunicationsCategory: Informational                                           Y. LeeISSN: 2070-1721                                                  Comcast                                                              O. Vautrin                                                        Juniper Networks                                                          September 2012                     6to4 Provider Managed TunnelsAbstract   6to4 Provider Managed Tunnels (6to4-PMT) provide a framework that 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 supplies 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 been successfully used in   a production network, implemented as open source code, and   implemented by a major routing vendor.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This is a contribution to the RFC Series, independently of any other   RFC stream.  The RFC Editor has chosen to publish this document at   its discretion and makes no statement about its value for   implementation or deployment.  Documents approved for publication by   the RFC Editor are not a candidate for any level of Internet   Standard; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6732.Kuarsingh, et al.             Informational                     [Page 1]

RFC 6732              6to4 Provider Managed Tunnels       September 2012Copyright Notice   Copyright (c) 2012 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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   to this document.Table of Contents1. Introduction ....................................................32. Motivation ......................................................33. 6to4 Provider Managed Tunnels ...................................53.1. 6to4 Provider Managed Tunnel Model .........................53.2.  Traffic Flow ..............................................53.3.  Prefix Translation ........................................63.4.  Translation State .........................................74. Deployment Considerations and Requirements ......................74.1. Customer Opt-Out ...........................................74.2. Shared CGN Space Considerations ............................84.3. End-to-End Transparency ....................................84.4. Path MTU Discovery Considerations ..........................94.5. Checksum Management ........................................94.6. Application Layer Gateways .................................94.7. Routing Requirements .......................................94.8. Relay Deployments .........................................105. Security Considerations ........................................106. Acknowledgements ...............................................107. References .....................................................117.1. Normative References ......................................117.2. Informative References ....................................11Kuarsingh, et al.             Informational                     [Page 2]

RFC 6732              6to4 Provider Managed Tunnels       September 20121.  Introduction   6to4 [RFC3056] tunneling, along with the anycast operation described   in [RFC3068], is widely deployed in modern Operating Systems and   off-the-shelf gateways sold throughout retail and Original Equipment   Manufacturer (OEM) channels.  Anycast-based 6to4 [RFC3068] allows for   tunneled 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 in which the consumer endpoints are downstream from a   northbound Carrier-Grade NAT (CGN) [RFC6264] function when assigned   non-RFC1918 IPv4 addresses, which are not routed on interdomain   links.   Operators that are actively deploying IPv6 networks and operate   legacy IPv4 access environments may want to utilize the existing 6to4   behavior 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 that 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 endeavor 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 toKuarsingh, et al.             Informational                     [Page 3]

RFC 6732              6to4 Provider Managed Tunnels       September 2012   the network edge and related transition technologies.  Many of the   new technologies available for IPv4 to IPv6 transition will require   the replacement of the organization's Customer Premises Equipment   (CPE) to support technologies like IPv6 Rapid Deployment (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 present in much of the equipment found in networks today that   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 is often on by default, and may be subject to erroneous   behavior.  The undesired behavior may be related to the use of   non-RFC1918 addresses on CPE equipment that 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 the 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 that 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 behaviors in end hosts [RFC6724].   6to4-PMT thus helps operators remove the impact of 6to4 in CGN   environments, deals with the fact that 6to4 is often on by default,   and allows access to IPv6-only endpoints from IPv4-only addressed   equipment.  Additionally, it provides relief from many challenges   related to mis-configurations in other networks that 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.Kuarsingh, et al.             Informational                     [Page 4]

RFC 6732              6to4 Provider Managed Tunnels       September 20123.  6to4 Provider Managed Tunnels3.1.  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 that translates the source 6to4 prefix to a   provider-assigned prefix that 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                                Functions/Platforms                    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.Kuarsingh, et al.             Informational                     [Page 5]

RFC 6732              6to4 Provider Managed Tunnels       September 2012        |  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 its 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 that maps the 6to4 2002::/16 prefix to   an appropriate provider assigned prefix.  In most cases, a ::/32   prefix would work best in 6to4-PMT that matches common Regional   Internet Registry (RIR) prefix assignments to operators.   The provider can use any prefix mapping strategy they so choose, but   the simpler the better.  Simple direct bitmapping 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 the 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 theKuarsingh, et al.             Informational                     [Page 6]

RFC 6732              6to4 Provider Managed Tunnels       September 2012   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 Mapping3.4.  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 employ 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 is not   within this scope of this document.4.  Deployment Considerations and Requirements4.1.  Customer Opt-Out   A provider enabling this function should offer 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 be assisted in turning off   6to4.Kuarsingh, et al.             Informational                     [Page 7]

RFC 6732              6to4 Provider Managed Tunnels       September 2012   Since the 6to4-PMT system is targeted at customers who are relatively   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 tunneling 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 its 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 occurring when shared address space [RFC6598] or Global Unicast   Addresses (GUA) are used behind a CGN and not routed on the Internet.   Non-RFC1918, yet unrouted (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 operator's 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 behavior.4.3.  End-to-End Transparency   The 6to4-PMT mode of 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 that provides connectivity that is uncontrolled and   often prone to high latency.  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   alternative.Kuarsingh, et al.             Informational                     [Page 8]

RFC 6732              6to4 Provider Managed Tunnels       September 20124.4.  Path MTU Discovery Considerations   The MTU will be subject to a reduced value due to standard 6to4   tunneling 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   accordingly.   It is also possible to pre-constrain the MTU at the upstream router   from the 6to4-PMT service agents that 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 in which   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 Application Layer Gateways (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   propagation).   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.  In that case, it is likely that the end network/customer   understands 6to4 and is maintaining their own relay environment andKuarsingh, et al.             Informational                     [Page 9]

RFC 6732              6to4 Provider Managed Tunnels       September 2012   therefore would not be subject to the operators 6to4 and/or PMT   operation.   Within their own network, the provider would also likely want to   advertise the 2002::/16 range to help bridge traditional 6to4 traffic   within the 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 neighboring Autonomous Systems   to prevent PMT operation for neighboring 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 that 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.  Security Considerations   6to4-PMT operation would be subject to the same security concerns as   normal 6to4 operation as described in [RFC6169].  6to4-PMT is also   not plainly perceptible by external hosts, and local entities appear   as native IPv6 hosts to the external hosts.6.  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   Donley.   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.Kuarsingh, et al.             Informational                    [Page 10]

RFC 6732              6to4 Provider Managed Tunnels       September 20127.  References7.1.  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 2001.7.2.  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.   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing              Architecture",RFC 4291, February 2006.   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "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",RFC5969, August 2010.   [RFC6169]  Krishnan, S., Thaler, D., and J. Hoagland, "Security              Concerns with IP Tunneling",RFC 6169, April 2011.   [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.Kuarsingh, et al.             Informational                    [Page 11]

RFC 6732              6to4 Provider Managed Tunnels       September 2012   [RFC6598]  Weil, J., Kuarsingh, V., Donley, C., Liljenstolpe, C., and              M. Azinger, "IANA-Reserved IPv4 Prefix for Shared Address              Space",BCP 153,RFC 6598, April 2012.   [RFC6724]  Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,              "Default Address Selection for Internet Protocol Version 6              (IPv6)",RFC 6724, September 2012.Authors' Addresses   Victor Kuarsingh (editor)   Rogers Communications   8200 Dixie Road   Brampton, Ontario L6T 0C1   Canada   EMail: victor.kuarsingh@gmail.com   URI:http://www.rogers.com   Yiu L. Lee   Comcast   One Comcast Center   Philadelphia, PA 19103   U.S.A.   EMail: yiu_lee@cable.comcast.com   URI:http://www.comcast.com   Olivier Vautrin   Juniper Networks   1194 N Mathilda Avenue   Sunnyvale, CA 94089   U.S.A.   EMail: olivier@juniper.net   URI:http://www.juniper.netKuarsingh, et al.             Informational                    [Page 12]