INTERNET DRAFT                                              C. Huitema
<draft-ietf-ipv6-deprecate-site-local-03.txt>                Microsoft
March 27, 2004                                            B. Carpenter
Expires September 27, 2004                                         IBM

              Deprecating Site Local Addresses

Status of this memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   This document is an Internet-Draft. Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
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   This document describes the issues surrounding the use of IPv6 site-
   local unicast addresses in their original form, and formally
   deprecates them. This deprecation does not prevent their continued
   use until a replacement has been standardized and implemented.

1       Introduction

   For some time, the IPv6 working group has been debating a set of
   issues surrounding the use of "site local" addresses. In its meeting
   in March 2003, the group reached a measure of agreement that these
   issues were serious enough to warrant a replacement of site local
   addresses in their original form. Although the consensus was far
   from unanimous, the working group confirmed in its meeting in July
   2003 the need to document these issues and the consequent decision
   to deprecate IPv6 site-local unicast addresses.

   Site-local addresses are defined in the IPv6 addressing architecture
   [RFC3513], especially in section 2.5.6.

   The remainder of this document describes the adverse effects of
   site-local addresses according to the above definition, and formally
   deprecates them.

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   Companion documents will describe the goals of a replacement
   solution and specify a replacement solution. However, the formal
   deprecation allows existing usage of site-local addresses to
   continue until the replacement is standardized and implemented.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2       Adverse effects of site local addresses

   Discussions in the IPv6 working group outlined several defects of
   the current site local addressing scope. These defects fall in two
   broad categories: ambiguity of addresses, and fuzzy definition of

   As currently defined, site local addresses are ambiguous: an address
   such as FEC0::1 can be present in multiple sites, and the address
   itself does not contain any indication of the site to which it
   belongs. This creates pain for developers of applications, for the
   designers of routers and for the network managers. This pain is
   compounded by the fuzzy nature of the site concept. We will develop
   the specific nature of this pain in the following section.

2.1     Developer pain, scope identifiers

   Early feedback from developers indicates that site local addresses
   are hard to use correctly in an application. This is particularly
   true for multi-homed hosts, which can be simultaneously connected to
   multiple sites, and for mobile hosts, which can be successively
   connected to multiple sites.

   Applications would learn or remember that the address of some
   correspondent was "FEC0::1234:5678:9ABC", they would try to feed the
   address in a socket address structure and issue a connect, and the
   call will fail because they did not fill up the "site identifier"
   variable, as in "FEC0::1234:5678:9ABC%1". (The use of the %
   character as a delimiter for site identifiers is specified in
   [SCOPING].) The problem is compounded by the fact that the site
   identifier varies with the host instantiation, e.g. sometimes %1 and
   sometimes %2, and thus that the host identifier cannot be remembered
   in memory, or learned from a name server.

   In short, the developer pain is caused by the ambiguity of site
   local addresses. Since site-local addresses are ambiguous,
   application developers have to manage the "site identifiers" that
   qualify the addresses of the hosts. This management of identifiers
   has proven hard to understand by developers, and also hard to
   execute by those developers who understand the concept.

2.2     Developer pain, local addresses

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   Simple client/server applications that do share IP addresses at the
   application layer are made more complex by IPv6 site-local
   addressing. These applications need to make intelligent decisions
   about the addresses that should and shouldn't be passed across site
   boundaries. These decisions, in practice, require that the
   applications acquire some knowledge of the network topology. Site
   local addresses may be used when client and server are in the same
   site, but trying to use them when client and server are in different
   sites may result in unexpected errors (i.e. connection reset by
   peer) or the establishment of connections with the wrong node.  The
   robustness and security implications of sending packets to an
   unexpected end-point will differ from application to application.

   Multi-party applications that pass IP addresses at the application
   layer present a particular challenge.  Even if a node can correctly
   determine whether a single remote node belongs or not to the local
   site, it will have no way of knowing where those addresses may
   eventually be sent.  The best course of action for these
   applications might be to use only global addresses.  However, this
   would prevent the use of these applications on isolated or
   intermittently connected networks that only have site-local
   addresses available, and might be incompatible with the use of site-
   local addresses for access control in some cases.

   In summary, the ambiguity of site local addresses leads to
   unexpected application behavior when application payloads carry
   these addresses outside the local site.

2.3     Manager pain, leaks

   The management of IPv6 site local addresses is in many ways similar
   to the management of RFC 1918 [RFC1918] addresses in some IPv4
   networks. In theory, the private addresses defined in RFC 1918
   should only be used locally, and should never appear in the
   Internet. In practice, these addresses "leak". The conjunction of
   leaks and ambiguity ends up causing management problems.

   Names and literal addresses of "private" hosts leak in mail
   messages, web pages, or files. Private addresses end up being used
   as source or destination of TCP requests or UDP messages, for
   example in DNS or trace-route requests, causing the request to fail,
   or the response to arrive at unsuspecting hosts.

   The experience with RFC1918 addresses also shows some non trivial
   leaks, besides pacing these addresses in IP headers. Private
   addresses also end up being used as targets of reverse DNS queries
   for RFC1918, uselessly overloading the DNS infrastructure. In
   general, many applications that use IP addresses directly end up
   passing RFC1918 addresses in application payloads, creating
   confusion and failures.

   The leakage issue is largely unavoidable. While some applications

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   are intrinsically scoped (e.g., Router Advertisement, Neighbor
   Discovery), most applications have no concept of scope, and no way
   of expressing scope. As a result, "stuff leaks across the borders".
   Since the addresses are ambiguous, the network managers cannot
   easily find out "who did it". Leaks are thus hard to fix, resulting
   in a lot of frustration.

2.4     Router pain, increased complexity

   The ambiguity of site local addresses also creates complications for
   the routers. In theory, site local addresses are only used within a
   contiguous site, and all routers in that site can treat them as if
   they were not ambiguous. In practice, special mechanisms are needed
   when sites are disjoint, or when routers have to handle several

   In theory, sites should never be disjoint. In practice, if site
   local addressing is used throughout a large network, some elements
   of the site will not be directly connected for example, due to
   network partitioning. This will create a demand to route the site-
   local packets across some intermediate network (such as the backbone
   area) that cannot be dedicated for a specific site. In practice,
   this leads to an extensive use of tunneling techniques, or the use
   of multi-sited routers, or both.

   Ambiguous addresses have fairly obvious consequences on multi-sited
   routers. In classic router architecture, the exit interface is a
   direct function of the destination address, as specified by a single
   routing table. However, if a router is connected to multiple sites,
   the routing of site local packets depends on the interface on which
   the packet arrived. Interfaces have to be associated to sites, and
   the routing entries for the site local addresses are site-dependent.
   Supporting this requires special provisions in routing protocols and
   techniques for routing and forwarding table virtualization that are
   normally used for VPNs. This contributes to additional complexity of
   router implementation and management.

   Network management complexity is also increased by the fact that
   though sites could be supported using existing routing constructs--
   such as domains and areas--the factors driving creation and setting
   the boundaries of sites are different from the factors driving those
   of areas and domains.

   In multi-homed routers, such as for example site border routers, the
   forwarding process should be complemented by a filtering process, to
   guarantee that packets sourced with a site local address never leave
   the site. This filtering process will in turn interact with the
   forwarding of packets, for example if implementation defects cause
   the drop of packets sent to a global address, even if that global
   address happen to belong to the target site.

   In summary, the ambiguity of site local addresses makes them hard to

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   manage in multi-sited routers, while the requirement to support
   disjoint sites and existing routing protocol constructs creates a
   demand for such routers.

2.5     Site is an ill-defined concept

   The current definition of scopes follows an idealized "concentric
   scopes" model. Hosts are supposed to be attached to a link, which
   belongs to a site, which belongs to the Internet. Packets could be
   sent to the same link, the same site, or outside that site. However,
   experts have been arguing about the definition of sites for years
   and have reached no sort of consensus. That suggests that there is
   in fact no consensus to be reached.

   Apart from link-local, scope boundaries are ill-defined. What is a
   site? Is the whole of a corporate network a site, or are sites
   limited to single geographic locations? Many networks today are
   split between an internal area and an outside facing "DMZ",
   separated by a firewall. Servers in the DMZ are supposedly
   accessible by both the internal hosts and external hosts on the
   Internet. Does the DMZ belong to the same site as the internal host?

   Depending on whom we ask, the definition of the site scope varies.
   It may map security boundaries, reachability boundaries, routing
   boundaries, QOS boundaries, administrative boundaries, funding
   boundaries, some other kinds of boundaries, or a combination of
   these. It is very unclear that a single scope could satisfy all
   these requirements.

   There are some well known and important scope-breaking phenomena,
   such as intermittently connected networks, mobile nodes, mobile
   networks, inter-domain VPNs, hosted networks, network merges and
   splits, etc. Specifically, this means that scope *cannot* be mapped
   into concentric circles such as a naive link/local/global model.
   Scopes overlap and extend into one another. The scope relationship
   between two hosts may even be different for different protocols.

   In summary, the current concept of site is naive, and does not map
   operational requirements.

3       Development of a better alternative

   The previous section reviewed the arguments against site-local
   addresses. Obviously, site locals also have some benefits, without
   which they would have been removed from the specification long ago.
   The perceived benefits of site local are that they are simple,
   stable, and private. However, it appears that these benefits can be
   also obtained with an alternative architecture, for example
   [Hinden/Haberman], in which addresses are not ambiguous and do not
   have a simple explicit scope.

   Having non-ambiguous address solves a large part of the developers'

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   pain, as it removes the need to manage site identifiers. The
   application can use the addresses as if they were regular global
   addresses, and the stack will be able to use standard techniques to
   discover which interface should be used. Some level of pain will
   remain, as these addresses will not always be reachable; however,
   applications can deal with the un-reachability issues by trying
   connections at a different time, or with a different address.
   Speculatively, a more sophisticated scope mechanism might be
   introduced at a later date.

   Having non ambiguous addresses will not eliminate the leaks that
   cause management pain. However, since the addresses are not
   ambiguous, debugging these leaks will be much simpler.

   Having non ambiguous addresses will solve a large part of the router
   issues: since addresses are not ambiguous, routers will be able to
   use standard routing techniques, and will not need different routing
   tables for each interface. Some of the pain will remain at border
   routers, which will need to filter packets from some ranges of
   source addresses; this is however a fairly common function.

   Avoiding the explicit declaration of scope will remove the issues
   linked to the ambiguity of the site concept. Non-reachability can be
   obtained by using "firewalls" where appropriate. The firewall rules
   can explicitly accommodate various network configurations, by
   accepting of refusing traffic to and from ranges of the new non-
   ambiguous addresses.

   One question remains, anycast addressing. Anycast addresses are
   ambiguous by construction, since they refer by definition to any
   host that has been assigned a given anycast address. Link-local or
   global anycast addresses can be "baked in the code". Further study
   is required on the need for anycast addresses with scope between
   link-local and global.

4       Deprecation

   This document formally deprecates the IPv6 site-local unicast prefix
   defined in [RFC3513], i.e. 1111111011 binary or FEC0::/10. The
   special behavior of this prefix MUST no longer be supported in new
   implementations. The prefix MUST NOT be reassigned for other use
   except by a future IETF standards action. Future versions of the
   addressing architecture [RFC3513] will include this information.

   However, router implementations SHOULD be configured to prevent
   routing of this prefix by default.

   The references to site local addresses should be removed as soon as
   practical from the revision of the Default Address Selection for
   Internet Protocol version 6 [RFC3484], the revision of the Basic
   Socket Interface Extensions for IPv6 [RFC3493], and from the
   revision of the Internet Protocol Version 6 (IPv6) Addressing

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   Architecture [RFC3513]. Incidental references to site local
   addresses should be removed from other IETF documents if and when
   they are updated.  These documents include [RFC2772, RFC2894,
   RFC3082, RFC3111, RFC3142, RFC3177, and RFC3316].

   Existing implementations and deployments MAY continue to use this

5       Security Considerations

   The use of ambiguous site-local addresses has the potential to
   adversely affect network security through leaks, ambiguity and
   potential misrouting, as documented in section 2. Deprecating the
   use of ambiguous addresses helps solving many of these problems.

   The site-local unicast prefix allows for some blocking action in
   firewall rules and address selection rules, which are commonly
   viewed as a security feature since they prevent packets crossing
   administrative boundaries. Such blocking rules can be configured for
   any prefix, including the expected future replacement for the site-
   local prefix. If these blocking rules are actually enforced, the
   deprecation of the site-local prefix does not endanger security.

6       IANA Considerations

   IANA is requested to mark the FEC0::/10 prefix as "deprecated",
   pointing to this document. Reassignment of the prefix for any usage
   requires justification via an IETF Standards Action [RFC2434].

7       Copyright

   The following copyright notice is copied from RFC 2026 [Bradner,
   1996], Section 10.4, and describes the applicable copyright for this

   Copyright (C) The Internet Society March 26, 2004. All Rights

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

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   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assignees.

   This document and the information contained herein is provided on an

8       Intellectual Property

   The following notice is copied from RFC 2026 [Bradner, 1996],
   Section 10.4, and describes the position of the IETF concerning
   intellectual property claims made against this document.

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use other technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication and any assurances
   of licenses to be made available, or the result of an attempt made
   to obtain a general license or permission for the use of such
   proprietary rights by implementers or users of this specification
   can be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive

9       Acknowledgements

   The authors would like to thank Fred Templin, Peter Bieringer,
   Chirayu Patel, Pekka Savola, and Alain Baudot for their review of
   the initial draft. The text of section 2.2 includes 2 paragraphs
   taken from a draft by Margaret Wasserman describing the impact of
   site local addressing. Alain Durand pointed out the need to revise
   existing RFC that make reference to site local addresses.

10      References

   Normative References

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

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   [RFC2434] Narten, T., and H. Alvestrand, "Guidelines for Writing an
   IANA Considerations Section in RFCs", RFC 2434, October 1998.

   [RFC3513] Hinden, R. and S. Deering, "IP Version 6 Addressing
   Architecture", RFC 3513, April 2003

   Informative references

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

   [Hinden/Haberman] Hinden, R. and B. Haberman, "Unique Local IPv6
   Unicast Addresses", work in progress.

   [RFC2772] Rockell, R. and R. Fink. "6Bone Backbone Routing
   Guidelines." RFC 2772, February 2000.

   [RFC2894] M. Crawford. "Router Renumbering for IPv6." RFC 2894,
   August 2000.

   [RFC3082] Kempf, J. and J. Goldschmidt. "Notification and
   Subscription for SLP." RFC 3082, March 2001.

   [RFC3111] E. Guttman. "Service Location Protocol Modifications for
   IPv6." RFC 3111, May 2001.

   [RFC3142] Hagino, J. and K. Yamamoto. "An IPv6-to-IPv4 Transport
   Relay Translator." RFC 3142, June 2001.

   [RFC3177] IAB, IESG. "IAB/IESG Recommendations on IPv6 Address." RFC
   3177, September 2001.

   [RFC3316] Arkko, J., Kuijpers, G., Soliman, H., Loughney, J. and J.
   Wiljakka. "Internet Protocol Version 6 (IPv6) for Some Second and
   Third Generation Cellular Hosts." RFC 3316, April 2003.

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

   [RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J. and W.
   Stevens. "Basic Socket Interface Extensions for IPv6." RFC 3493,
   February 2003.

   [SCOPING] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
   B. Zill, "IPv6 Scoped Address Architecture", work in progress.

11      Authors' Addresses

   Christian Huitema
   Microsoft Corporation

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   One Microsoft Way
   Redmond, WA 98052-6399

   Brian Carpenter
   IBM Corporation
   Sauemerstrasse 4
   8803 Rueschlikon

12      History of changes

12.1    Changes from draft-00 to draft-01

   Changed the text in the introduction to say that the decision was
   "confirmed" in July 2003.

   Add some explanatory text in section 2.2, address leak, and section
   2.3, routing pain.

   In section 4, and 5 change the erroneous "link local" to "site

   Add a reference to RFC 2119 describing the use of keywords.

   In section 5, qualify that the replacement of site local is only as
   secure if blocking rules are actually implemented at site

12.2    Changes from draft-01 to draft-02

   Inserted a new section "2.2 Developer pain, local addresses" to
   capture the pain caused by ambiguous addresses carried in
   application payloads.

   Added a paragraph in section 4 recommending the removal of
   references to site local addresses from several RFC. Added these RFC
   to the Reference section.

   Removed the reference to the draft "Addressing Requirements for
   Local Communications within Sites", in order to avoid references to
   drafts that may slow down document publication.

12.3    Changes from draft-02 to draft-03

   The changes from draft 02 to draft 03 take into account the IESG

   A reference to the scoped addresses architecture draft has been
   added to section 2.1, in order to explain the usage of the % sign to

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   document site numbers in site local addresses.

   Section 2.4 has been reworded following suggestions by Alex Zinin,
   essentially to change the tone from "this creates a problem" to
   "this would increase router implementation and management

   A new paragraph has been added to the security considerations,
   reiterating the issues due to ambiguity which were brought up in the
   preceding sections.

   The IANA considerations have been rewritten for greater precision.

   A duplicate reference to RFC 3513 has been removed.

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