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Network Working Group                                         C. HuitemaRequest for Comments: 3879                                     MicrosoftCategory: Standards Track                                   B. Carpenter                                                                     IBM                                                          September 2004Deprecating Site Local AddressesStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2004).Abstract   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 insection 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.Huitema & Carpenter         Standards Track                     [Page 1]

RFC 3879            Deprecating Site Local Addresses      September 2004   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",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described inBCP 14,RFC 2119   [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 sites.   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 zone 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 theHuitema & Carpenter         Standards Track                     [Page 2]

RFC 3879            Deprecating Site Local Addresses      September 2004   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   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 ofRFC 1918 [RFC1918] addresses in some IPv4   networks.  In theory, the private addresses defined inRFC 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.Huitema & Carpenter         Standards Track                     [Page 3]

RFC 3879            Deprecating Site Local Addresses      September 2004   The experience withRFC 1918 addresses also shows some non trivial   leaks, besides placing these addresses in IP headers.  Private   addresses also end up being used as targets of reverse DNS queries   forRFC 1918, uselessly overloading the DNS infrastructure.  In   general, many applications that use IP addresses directly end up   passingRFC 1918 addresses in application payloads, creating   confusion and failures.   The leakage issue is largely unavoidable.  While some applications   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   sites.   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.Huitema & Carpenter         Standards Track                     [Page 4]

RFC 3879            Deprecating Site Local Addresses      September 2004   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   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 mappedHuitema & Carpenter         Standards Track                     [Page 5]

RFC 3879            Deprecating Site Local Addresses      September 2004   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'   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.Huitema & Carpenter         Standards Track                     [Page 6]

RFC 3879            Deprecating Site Local Addresses      September 2004   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 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, andRFC3316].   Existing implementations and deployments MAY continue to use this   prefix.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 insection 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.Huitema & Carpenter         Standards Track                     [Page 7]

RFC 3879            Deprecating Site Local Addresses      September 20046.  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.  Acknowledgements   The authors would like to thank Fred Templin, Peter Bieringer,   Chirayu Patel, Pekka Savola, and Alain Baudot for their review of the   initial version of the document.  The text ofsection 2.2 includes 2   paragraphs taken from a version 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.8.  References8.1.  Normative References   [RFC2119]         Bradner, S., "Key words for use in RFCs to Indicate                     Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2434]         Narten, T. and H. Alvestrand, "Guidelines for                     Writing an IANA Considerations Section in RFCs",BCP 26,RFC 2434, October 1998.   [RFC3513]         Hinden, R. and S. Deering, "Internet Protocol                     Version 6 (IPv6) Addressing Architecture",RFC3513, April 2003.8.2.  Informative References   [RFC1918]         Rekhter, Y., Moskowitz, B., Karrenberg, D., de                     Groot, G., and E. Lear, "Address Allocation for                     Private Internets",BCP 5,RFC 1918, February 1996.   [RFC2772]         Rockell, R. and R. Fink, "6Bone Backbone Routing                     Guidelines",RFC 2772, February 2000.   [RFC2894]         Crawford, M., "Router Renumbering for IPv6",RFC2894, August 2000.   [RFC3082]         Kempf, J. and J. Goldschmidt, "Notification and                     Subscription for SLP",RFC 3082, March 2001.Huitema & Carpenter         Standards Track                     [Page 8]

RFC 3879            Deprecating Site Local Addresses      September 2004   [RFC3111]         Guttman, E., "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 and 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]         Draves, R., "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.   [Hinden/Haberman] Hinden, R. and B. Haberman, "Unique Local IPv6                     Unicast Addresses", Work in Progress, June 2004.   [SCOPING]         Deering, S., Haberman, B., Jinmei, T., Nordmark,                     E., and B. Zill, "IPv6 Scoped Address                     Architecture", Work in Progress, August 2004.9.  Authors' Addresses   Christian Huitema   Microsoft Corporation   One Microsoft Way   Redmond, WA 98052-6399   USA   EMail: huitema@microsoft.com   Brian Carpenter   IBM Corporation   Sauemerstrasse 4   8803 Rueschlikon   Switzerland   EMail: brc@zurich.ibm.comHuitema & Carpenter         Standards Track                     [Page 9]

RFC 3879            Deprecating Site Local Addresses      September 200410.  Full Copyright Statement   Copyright (C) The Internet Society (2004).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/S HE   REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE   INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR   IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the IETF's procedures with respect to rights in IETF Documents can   be found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat 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 on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Huitema & Carpenter         Standards Track                    [Page 10]