One document matched: draft-ietf-ipv6-deprecate-site-local-00.txt
INTERNET DRAFT C. Huitema
< draft-ietf-ipv6-deprecate-site-local-00.txt> Microsoft
August 16, 2003 B. Carpenter
Expires February 16, 2003 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
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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 decided in its meeting in July
2003 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 [Hain/Templin] and specify a replacement solution
[Hinden/Haberman]. However, the formal deprecation allows existing
usage of site-local addresses to continue until the replacement is
standardized and implemented.
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
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 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 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
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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. Private addresses
also end up being used as targets of reverse lookup requests in the
DNS, uselessly overloading the DNS infrastructure.
The leakage issue is largely unavoidable. While some applications
are intrinsically scoped (eg. RA, ND), 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.
2.3 Router pain, routing tables
The ambiguity of site local addresses also creates problems 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, problem occurs 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. This will create a
demand to route the site-local packets across some intermediate
network. 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.
The route management software and the routing protocols have to
account for the site boundaries.
In multi-homed routers, such as for example site border routers, the
routing 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
routing of packets, as it may 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 creates a demand for such routers.
2.4 Site is an ill-defined concept
The current definition of scopes follows an idealized "concentric
scope" 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. 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 [Hain/Templin]. 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
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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 link-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.
Existing implementations and deployments MAY continue to use this
prefix.
5 Security Considerations
The link-local unicast prefix allows for some blocking action in
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firewall rules and address selection rules, which are commonly
viewed as a security feature since they prevent packets crossing
administrative boundaries. However, such blocking rules can be
configured for any prefix, including the expected future replacement
for the site-local prefix. Thus the deprecation of the site-local
prefix does not endanger security.
6 IANA Considerations
IANA is specifically requested not to reassign the 1111111011 binary
or FEC0::/10 prefix unless requested to do so by a future IETF
standards action.
7 Copyright
The following copyright notice is copied from RFC 2026 [Bradner,
1996], Section 10.4, and describes the applicable copyright for this
document.
Copyright (C) The Internet Society August 13, 2003. All Rights
Reserved.
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
English.
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
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS 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.
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.
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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
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The IETF invites any interested party to bring to its attention any
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9 Acknowledgements
10 References
Normative References
[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
[Hain/Templin] Hain, T. and F. Templin, "Addressing Requirements for
Local Communications within Sites", work in progress.
[Hinden/Haberman] Hinden, R. and B. Haberman, "Unique Local IPv6
Unicast Addresses", work in progress.
11 Authors' Addresses
Christian Huitema
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
USA
Email: huitema@microsoft.com
Brian Carpenter
IBM Corporation
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Sauemerstrasse 4
8803 Rueschlikon
Switzerland
Email: brc@zurich.ibm.com
Carpenter, Huitema. [Page 8]
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