RFC 7526
Deprecating the Anycast Prefix for 6to4 Relay Routers
RFC 7526: Deprecating the Anycast Prefix for 6to4 Relay Routers ✨
Okay bestie, let's get into RFC 7526 🦋. It's from the Internet Engineering Task Force (IETF) and is a Best Current Practice (BCP: 196, ISSN 2070-1721). O. Troan from Cisco and B. Carpenter, Ed. from the Univ. of Auckland wrote it, and it was published in May 2015 as Request for Comments: 7526. It obsoletes RFC 3068 and RFC 6732, and it's the doc asking those two to be moved to Historic status. Iconic energy 👑
Abstract 🌸
Okay so the 6to4 transition mechanism from RFC 3056 ("Connection of IPv6 Domains via IPv4 Clouds") has been through it 😭. Experience shows it's just not suitable for widespread deployment and use on the Internet when it's used in its anycast mode. So this doc requests that RFC 3068 ("An Anycast Prefix for 6to4 Relay Routers") and RFC 6732 ("6to4 Provider Managed Tunnels") be made obsolete and moved to Historic status. It recommends that future products should not support 6to4 anycast and that existing deployments should be reviewed. This complements the guidelines in RFC 6343 💅
Status of This Memo ✨
This memo documents an Internet Best Current Practice.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on BCPs is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7526.
Copyright Notice 🎀
Copyright (c) 2015 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 (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. 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
1.1. Related Work . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. 6to4 Operational Problems . . . . . . . . . . . . . . . . . . 4
4. Deprecation . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Implementation Recommendations . . . . . . . . . . . . . . . 5
6. Operational Recommendations . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 101. Introduction 💖
The original form of the 6to4 transition mechanism [RFC3056] relies on unicast addressing. However, its extension specified in "An Anycast Prefix for 6to4 Relay Routers" [RFC3068] has been shown to have severe practical problems when used in the Internet. This document requests that RFCs 3068 and 6732 be moved to Historic status, as defined in Section 4.2.4 of [RFC2026]. It complements the deployment guidelines in [RFC6343].
6to4 was designed to help transition the Internet from IPv4 to IPv6. It has been a good mechanism for experimenting with IPv6, but because of the high failure rates seen with anycast 6to4 [HUSTON], end users may end up disabling IPv6 on hosts. This has resulted in some content providers being reluctant to make content available over IPv6 in the past. 🙈
[RFC6343] analyzes the known operational issues in detail and describes a set of suggestions to improve 6to4 reliability, given the widespread presence of hosts and customer premises equipment that support it. The advice to disable 6to4 by default has been widely adopted in recent operating systems, and the failure modes have been widely hidden from users by many browsers adopting the "Happy Eyeballs" approach [RFC6555].
Nevertheless, a measurable amount of 6to4 traffic is still observed by IPv6 content providers. The remaining successful users of anycast 6to4 are likely to be on hosts using the obsolete policy table [RFC3484] (which prefers 6to4 above IPv4) and running without Happy Eyeballs. Furthermore, they must have a route to an operational anycast relay and they must be accessing an IPv6 host that has a route to an operational return relay.
However, experience shows that operational failures caused by anycast 6to4 have continued despite the advice in RFC 6343 being available. 😭
1.1. Related Work 🦋
"IPv6 Rapid Deployment on IPv4 Infrastructures (6rd) -- Protocol Specification" [RFC5969] explicitly builds on the 6to4 mechanism, using a service provider prefix instead of 2002::/16. However, the deployment model is based on service provider support such that 6rd avoids the problems observed with anycast 6to4.
The framework for "6to4 Provider Managed Tunnels" [RFC6732] is intended to help a service provider manage 6to4 anycast tunnels. This framework only exists because of the problems observed with anycast 6to4.
2. Conventions 🌈
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].
In this document, the word "deprecate" and its derivatives are used only in their generic sense of "criticize or express disapproval" and do not have any specific normative meaning. A deprecated function might exist in the Internet for many years to allow backwards compatibility.
3. 6to4 Operational Problems 🍓
6to4 is a mechanism designed to allow isolated IPv6 islands to reach each other using IPv6-over-IPv4 automatic tunneling. To reach the native IPv6 Internet, the mechanism uses relay routers in both the forward and reverse direction. The mechanism is supported in many IPv6 implementations. With the increased deployment of IPv6, the mechanism has been shown to have a number of shortcomings.
In the forward direction, a 6to4 node will send IPv4-encapsulated IPv6 traffic to a 6to4 relay that is connected to both the 6to4 cloud and native IPv6. In the reverse direction, a 2002::/16 route is injected into the native IPv6 routing domain to attract traffic from native IPv6 nodes to a 6to4 relay router. It is expected that traffic will use different relays in the forward and reverse direction.
One model of 6to4 deployment, described in Section 5.2 of RFC 3056, suggests that a 6to4 router should have a set of managed connections (via BGP connections) to a set of 6to4 relay routers. While this makes the forward path more controlled, it does not guarantee a functional reverse path. In any case, this model has the same operational burden as manually configured tunnels and has seen no deployment in the public Internet.
RFC 3068 adds an extension that allows the use of a well-known IPv4 anycast address to reach the nearest 6to4 relay in the forward direction. However, this anycast mechanism has a number of operational issues and problems, which are described in detail in Section 3 of [RFC6343]. This document is intended to deprecate the anycast mechanism.
Peer-to-peer usage of the 6to4 mechanism exists in the Internet, likely unknown to many operators. This usage is harmless to third parties and is not dependent on the anycast 6to4 mechanism that this document deprecates.
4. Deprecation 🚫
This document formally deprecates the anycast 6to4 transition mechanism defined in [RFC3068] and the associated anycast IPv4 address 192.88.99.1. It is no longer considered to be a useful service of last resort.
The prefix 192.88.99.0/24 MUST NOT be reassigned for other use except by a future IETF Standards Action.
The basic unicast 6to4 mechanism defined in [RFC3056] and the associated 6to4 IPv6 prefix 2002::/16 are not deprecated. The default address selection rules specified in [RFC6724] are not modified.
In the absence of 6to4 anycast, "6to4 Provider Managed Tunnels" [RFC6732] will no longer be necessary, so they are also deprecated by this document.
Incidental references to 6to4 should be reviewed and possibly removed from other IETF documents if and when they are updated. These documents include RFC 3162, RFC 3178, RFC 3790, RFC 4191, RFC 4213, RFC 4389, RFC 4779, RFC 4852, RFC 4891, RFC 4903, RFC 5157, RFC 5245, RFC 5375, RFC 5971, RFC 6071, and RFC 6890.
5. Implementation Recommendations 🔥
It is NOT RECOMMENDED to include the anycast 6to4 transition mechanism in new implementations. If included in any implementations, the anycast 6to4 mechanism MUST be disabled by default.
In host implementations, unicast 6to4 MUST also be disabled by default. All hosts using 6to4 MUST support the IPv6-address-selection policy described in [RFC6724].
In router implementations, 6to4 MUST be disabled by default. In particular, enabling IPv6 forwarding on a device MUST NOT automatically enable 6to4.
6. Operational Recommendations 🌸
Okay so this doc is NOT saying you should go filtering traffic or routes for 6to4, or even anycast 6to4 🙅♀️. What it does do is recommend against any further deployment of the anycast 6to4 mechanism, ask current 6to4 deployments to check whether continuing to use anycast 6to4 is actually worth it, and give recommendations so that 6to4 doesn't get in the way of native IPv6 being deployed and used across the whole Internet. It's giving "don't let the old thing block the good thing" 💜.
Networks SHOULD NOT filter out packets whose source address is 192.88.99.1, because that's normal 6to4 traffic coming from a 6to4 return relay somewhere out on the Internet 🦋. That also means making sure traffic from a local 6to4 return relay with a source address of 192.88.99.1 gets through anti-spoofing filters (like the ones described in [RFC2827] and [RFC3704]) or through Unicast Reverse Path Forwarding (uRPF) checks [RFC5635]. Don't let your own filters block your own relay, bestie 💀.
The guidelines in Section 4 of [RFC6343] still apply to anyone who decides to keep running anycast 6to4 even though it's deprecated 🧚.
Current operators of an anycast 6to4 relay with the IPv4 address 192.88.99.1 SHOULD review the information in [RFC6343] and this document, and then think carefully about whether the anycast relay can be shut down as traffic dies down 🍓. Internet service providers that don't operate an anycast relay but do give their customers a route to 192.88.99.1 SHOULD verify that the route actually leads to a working anycast relay, as discussed in Section 4.2.1 of [RFC6343] ✨. Also, Internet service providers and other network providers MUST NOT originate a route to 192.88.99.1, unless they actively operate and monitor an anycast 6to4 relay service as detailed in Section 4.2.1 of [RFC6343]. That one is a hard no unless you're really running it, no cap 🚫.
Operators of a 6to4 return relay responding to the IPv6 prefix 2002::/16 SHOULD review the information in [RFC6343] and this document, and then think carefully about whether the return relay can be shut down as traffic dies down 🌈. Quick heads-up: nothing in the design of 6to4 assumes or requires that return packets are handled by the same relay as outbound packets, so don't get confused about that 🙈. As discussed in Section 4.5 of RFC 6343, content providers might choose to keep running a return relay for the benefit of their own leftover 6to4 clients 🫶. Internet service providers SHOULD announce the IPv6 prefix 2002::/16 to their own customers if and only if it leads to a correctly operating return relay as described in RFC 6343 💅. IPv6-only service providers, including those running a NAT64 service [RFC6146], are advised that their own customers need a route to such a relay, in case a leftover 6to4 user served by a different service provider tries to talk to them. Main character energy for the people who need to plan around everyone else 👑.
Operators of "6to4 Provider Managed Tunnels" [RFC6732] SHOULD carefully consider when this service can be discontinued as traffic dies down 🎀.
7. IANA Considerations ✨
Okay, IANA stuff 📋. The document that created the "IANA IPv4 Special-Purpose Address Registry" [RFC6890] included the 6to4 Relay Anycast prefix (192.88.99.0/24) as Table 10. Per this document, IANA has marked the 192.88.99.0/24 prefix (originally defined by [RFC3068]) as "Deprecated (6to4 Relay Anycast)" and added a reference to this RFC 🦋. The Boolean values for the address block 192.88.99.0/24 have been removed 🧹. Redelegating this prefix for any use needs justification via an IETF Standards Action [RFC5226], so it's not happening by accident 🔒.
8. Security Considerations 💀
Okay, this one's short and sweet 🙏. There are no new security considerations pertaining to this document. General security issues with tunnels are listed in [RFC6169], and the 6to4-specific ones are in [RFC3964] and [RFC6324]. Go read those, they are seriously important 🚨.
9. References 📚
9.1. Normative References
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, DOI 10.17487/RFC2026, October 1996,
<http://www.rfc-editor.org/info/rfc2026>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
May 2000, <http://www.rfc-editor.org/info/rfc2827>.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, DOI 10.17487/RFC3056, February
2001, <http://www.rfc-editor.org/info/rfc3056>.
[RFC3068] Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
RFC 3068, DOI 10.17487/RFC3068, June 2001,
<http://www.rfc-editor.org/info/rfc3068>.
[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March
2004, <http://www.rfc-editor.org/info/rfc3704>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <http://www.rfc-editor.org/info/rfc6146>.
[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
<http://www.rfc-editor.org/info/rfc6724>.
[RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman,
"Special-Purpose IP Address Registries", BCP 153,
RFC 6890, DOI 10.17487/RFC6890, April 2013,
<http://www.rfc-editor.org/info/rfc6890>.9.2. Informative References
[HUSTON] Huston, G., "Flailing IPv6", The ISP Column, December
2010,
<http://www.potaroo.net/ispcol/2010-12/6to4fail.html>.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484,
DOI 10.17487/RFC3484, February 2003,
<http://www.rfc-editor.org/info/rfc3484>.
[RFC3964] Savola, P. and C. Patel, "Security Considerations for
6to4", RFC 3964, DOI 10.17487/RFC3964, December 2004,
<http://www.rfc-editor.org/info/rfc3964>.
[RFC5635] Kumari, W. and D. McPherson, "Remote Triggered Black Hole
Filtering with Unicast Reverse Path Forwarding (uRPF)",
RFC 5635, DOI 10.17487/RFC5635, August 2009,
<http://www.rfc-editor.org/info/rfc5635>.
[RFC5969] Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd) -- Protocol Specification",
RFC 5969, DOI 10.17487/RFC5969, August 2010,
<http://www.rfc-editor.org/info/rfc5969>.
[RFC6169] Krishnan, S., Thaler, D., and J. Hoagland, "Security
Concerns with IP Tunneling", RFC 6169,
DOI 10.17487/RFC6169, April 2011,
<http://www.rfc-editor.org/info/rfc6169>.
[RFC6324] Nakibly, G. and F. Templin, "Routing Loop Attack Using
IPv6 Automatic Tunnels: Problem Statement and Proposed
Mitigations", RFC 6324, DOI 10.17487/RFC6324, August 2011,
<http://www.rfc-editor.org/info/rfc6324>.
[RFC6343] Carpenter, B., "Advisory Guidelines for 6to4 Deployment",
RFC 6343, DOI 10.17487/RFC6343, August 2011,
<http://www.rfc-editor.org/info/rfc6343>.
[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, DOI 10.17487/RFC6555, April
2012, <http://www.rfc-editor.org/info/rfc6555>.
[RFC6732] Kuarsingh, V., Ed., Lee, Y., and O. Vautrin, "6to4
Provider Managed Tunnels", RFC 6732, DOI 10.17487/RFC6732,
September 2012, <http://www.rfc-editor.org/info/rfc6732>.Acknowledgements 🫶
The authors would like to acknowledge Tore Anderson, Mark Andrews, Dmitry Anipko, Jack Bates, Cameron Byrne, Ben Campbell, Lorenzo Colitti, Gert Doering, Nick Hilliard, Philip Homburg, Ray Hunter, Joel Jaeggli, Victor Kuarsingh, Kurt Erik Lindqvist, Jason Livingood, Jeroen Massar, Keith Moore, Tom Petch, Daniel Roesen, Mark Townsley, and James Woodyatt for their contributions and discussions on this topic 💖.
Special thanks go to Fred Baker, David Farmer, Wes George, and Geoff Huston for their significant contributions 👑.
Many thanks to Gunter Van de Velde for documenting the harm caused by non-managed tunnels and stimulating the creation of this document 🧚.
Authors' Addresses 💌
Ole Troan
Cisco
Oslo
Norway
EMail: ot@cisco.com
Brian Carpenter (editor)
Department of Computer Science
University of Auckland
PB 92019
Auckland 1142
New Zealand
EMail: brian.e.carpenter@gmail.com📦 where this page comes from
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