Internet DRAFT - draft-ietf-6man-rfc6874bis
draft-ietf-6man-rfc6874bis
6MAN B. Carpenter
Internet-Draft Univ. of Auckland
Obsoletes: 6874 (if approved) S. Cheshire
Updates: 3986, 3987 (if approved) Apple Inc.
Intended status: Standards Track R. Hinden
Expires: 3 January 2024 Check Point Software
2 July 2023
Representing IPv6 Zone Identifiers in Address Literals and Uniform
Resource Identifiers
draft-ietf-6man-rfc6874bis-09
Abstract
This document describes how the zone identifier of an IPv6 scoped
address, defined as <zone_id> in the IPv6 Scoped Address Architecture
(RFC 4007), can be represented in a literal IPv6 address and in a
Uniform Resource Identifier that includes such a literal address. It
updates the URI Generic Syntax and Internationalized Resource
Identifier specifications (RFC 3986, RFC 3987) accordingly, and
obsoletes RFC 6874.
Discussion Venue
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the 6MAN mailing list
(ipv6@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/ipv6/
(https://mailarchive.ietf.org/arch/browse/ipv6/).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 3 January 2024.
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Copyright Notice
Copyright (c) 2023 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 (https://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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Issues with Implementing RFC 6874 . . . . . . . . . . . . . . 5
3. Specification . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Scope and Deployment . . . . . . . . . . . . . . . . . . . . 8
5. URI Parsers . . . . . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Options Considered . . . . . . . . . . . . . . . . . 15
Appendix B. Change log . . . . . . . . . . . . . . . . . . . . . 16
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
The Uniform Resource Identifier (URI) syntax specification [RFC3986]
defined how a literal IPv6 address can be represented in the "host"
part of a URI. Later, the IPv6 Scoped Address Architecture
specification [RFC4007] extended the text representation of limited-
scope IPv6 addresses such that a zone identifier may be concatenated
to a literal address, for purposes described in that specification.
Zone identifiers are especially useful in contexts in which literal
addresses are typically used, for example, during fault diagnosis,
when it may be essential to specify which interface is used for
sending to a link-local address. It should be noted that zone
identifiers have purely local meaning within the node in which they
are defined, usually being the same as IPv6 interface names. They
are completely meaningless for any other node. Today, they are
meaningful only when attached to link-local addresses, but it is
possible that other uses might be defined in the future.
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The IPv6 Scoped Address Architecture specification does not specify
how zone identifiers are to be represented in URIs. Practical
experience has shown that this feature is necessary in various use
cases, including the following:
1. A web browser may be used for simple debugging actions involving
link-local addresses on a host with more than one active link
interface. For example, the existence of a device may today be
checked via "ping fe80::1234%eth0" but not via
"https://[fe80::1234%eth0]".
2. A web browser must sometimes be used to configure or reconfigure
a device which only has a link-local address and whose only
configuration tool is a web server, again in a host with more
than one active link interface. For example, a typical home
router may today be configured via "http://192.168.178.1" but not
via "http://[fe80::1%eth0]".
3. The Apple and open-source CUPS printing mechanism [CUPS]
[OP-CUPS] uses an HTTP-based protocol [RFC3510][RFC7472] to
establish link-local relationships, so requires the specification
of the relevant interface.
4. The Microsoft Web Services for Devices (WSD) virtual printer port
mechanism can generate an IPv6 link-local URL such as
"http://[fe80::823b:f9ff:fe7b:d9dc%10]:80/WebServices/Device" in
which the zone identifier is present, but is not recognized by
any current browser.
5. The National Marine Electronics Association (NMEA) has recently
defined its "OneNet Marine IPv6 Ethernet Networking Standard"
[ONE-NET], which includes a specific requirement for device
configuration via a browser using link-local addresses. Such
requirements have already spawned a hack to work around the
current limitation [LL-HACK].
For these use cases, it is highly desirable that a complete IPv6
link-local address can be cut and pasted from one context (such as
the output from a system command) to another (such as a browser
dialogue box). Since such addresses may include quite long
hexadecimal strings, any solution except cut-and-paste is highly
error prone.
The use cases listed above apply to relatively simple actions on end
systems. The zone identifiers that can be used are limited by the
character set allowed in URIs. In particular, upper case letters and
most non-alphanumeric characters are intrinsically problematic in the
host part of a URI. This is not an issue on typical end systems,
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which generally use lower case alphanumeric interface names, but it
is likely to arise, for example, in network infrastructure devices.
These may have large numbers of interfaces, which are commonly named
for network management purposes in styles such as "Ethernet1/0/1" or
"ge-0/0/0.0", reflecting the hardware structure and depending on the
manufacturer. Generally speaking, such names are handled by various
network management mechanisms and specialized commands, and do not
need to be included in URIs. Nevertheless, we describe below how an
interface name containing non-conforming characters can be replaced
by a numeric value in case it is needed in a URI.
For avoidance of doubt, devices whose network stack does not support
the RFC 4007 model of a readable Zone ID plus a numeric index are out
of scope for this document.
As IPv6 deployment becomes widespread, the lack of a solution for
handling complete link-local addresses in web browsers is becoming an
acute problem for increasing numbers of operational and support
personnel. It will become critical as IPv6-only networks, with no
native IPv4 support, appear. For example, the NMEA use case
mentioned above is an immediate requirement. This is the principal
reason for documenting this requirement and its solution now.
It should be noted that whereas some operating systems and network
APIs support a default zone identifier as recommended by the IPv6
scoped address architecture [RFC4007], others do not, and for them an
appropriate URI syntax is particularly important.
In the past, some browser versions directly accepted the IPv6 Scoped
Address syntax for scoped IPv6 addresses embedded in URIs, i.e., they
were coded to interpret a "%" sign following the literal address as
introducing a zone identifier, instead of introducing two hexadecimal
characters representing some percent-encoded octet as explained in
Section 2.1 of [RFC3986]. Clearly, interpreting the "%" sign as
introducing a zone identifier is very convenient for users, although
it is not supported by the URI syntax in RFC 3986 or the
Internationalized Resource Identifier (IRI) syntax in [RFC3987].
Therefore, this document updates RFC 3986 and RFC 3987 by adding
syntax to allow a zone identifier to be included in a literal IPv6
address within a URI.
In contexts other than a user interface, a zone identifier is mapped
into a numeric zone index or interface number. The MIB textual
convention InetZoneIndex [RFC4001] and the socket interface [RFC3493]
define this as a 32-bit unsigned integer. (However, note that
interface numbers are limited to positive signed 32-bit integers (see
InterfaceIndex defined in [RFC2863] and if-index defined in
[RFC8343]) while the zone index allows for unsigned 32-bit integers.)
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The mapping between the human-readable zone identifier string and the
numeric value is a host-specific function that varies between
operating systems. The present document is concerned only with the
human-readable string that is typically displayed in an operating
system's user interface. However, in most operating systems it is
possible to use the underlying interface number, represented as a
decimal integer, as an equivalent to the human-readable string. This
is recommended by Section 11.2 of RFC 4007, but not required. This
provides a solution for cases where the assigned zone identifier uses
characters not allowed in a URI. The user must find the interface
number corresponding to the displayed interface name. For example,
on Linux, a user can determine interface numbers by issuing the
command "ip link show" and then use "fe80::1%5" instead of
"fe80::1%Ethernet+0+1", if the interface number happens to be 5. In
such operating systems, the decimal integer can be used in a URI in
place of the zone identifier, although this does not allow cut-and-
paste of the human-readable identifier.
Several alternative solutions were considered while this document was
developed. Appendix A briefly describes the various options and
their advantages and disadvantages.
This document obsoletes its predecessor [RFC6874] by greatly
simplifying its recommendations and requirements for URI parsers.
Its effect on the formal URI syntax [RFC3986] is different from that
of RFC 6874.
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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Issues with Implementing RFC 6874
Several issues prevented RFC 6874 being implemented in browsers:
1. There was some disagreement with requiring percent-encoding of
the "%" sign preceding a zone identifier. This requirement is
dropped in the present document.
2. The requirement to delete any zone identifier before emitting a
URI from the host in an HTTP message was considered both too
complex to implement and in violation of normal HTTP practice
[RFC9110], although required by Section 11.2 of RFC 4007. This
requirement has been dropped from the present document.
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3. The suggestion to pragmatically allow a bare "%" sign when this
would be unambiguous was considered both too complex to implement
and confusing for users. This suggestion has been dropped from
the present document since it is now irrelevant.
3. Specification
According to the IPv6 Scoped Address syntax [RFC4007], a zone
identifier is attached to the textual representation of an IPv6
address by concatenating "%" followed by <zone_id>, where <zone_id>
is a string identifying the zone of the address. However, the IPv6
Scoped Address Architecture specification gives no precise definition
of the character set allowed in <zone_id>. There are no rules or de
facto standards for this. For example, the first Ethernet interface
in a host might be called %0, %1, %25, %en1, %eth0, or whatever the
implementer happened to choose.
This lack of precision leads to two specific difficulties when set
against the general rules for the host subcomponent of a URI
[RFC3986]:
1. The URI host component is case-insensitive. RFC 4007 implies
case sensitivity.
2. The URI host component must be composed from a specific character
set. RFC 4007 simply requires an ASCII string.
The syntax specified below clarifies these two items.
In a URI, a literal IPv6 address is always embedded between "[" and
"]". This document specifies how a zone identifier can be appended
to the address. The URI syntax defined by RFC 3986 does not allow
the presence of a percent ("%") character within an IPv6 address
literal. For this reason, it is backwards compatible to allow the
use of "%" within an IPv6 address literal as a delimiter only, such
that the scoped address "fe80::abcd%en1" would appear in a URI as
"http://[fe80::abcd%en1]" or "https://[fe80::abcd%en1]".
This use of "%" as a delimiter applies only within an IPv6 address
literal, and is irrelevant to and exempt from the percent-encoding
mechanism of RFC 3986.
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A zone identifier used in a URI MUST contain only ASCII characters
classified as "unreserved" for use in URIs by RFC 3986. This
excludes characters such as "/", "]" or even "%" that would
complicate parsing. For the avoidance of doubt, note that a zone
identifier consisting of "25" or starting with "25" is valid and is
used in some operating systems. A parser MUST NOT apply percent
decoding to the IPv6 address literal in a URI, including cases such
as "http://[fe80::abcd%25]" and "http://[fe80::abcd%25xy]".
If an operating system uses any characters in zone or interface
identifiers that are not in the "unreserved" character set,
identifiers including them cannot be used in a URI.
Section 6.2.2.1 of RFC 3986 states unambiguously that "the scheme and
host are case-insensitive and therefore should be normalized to
lowercase". Therefore, even if an operating system supports case-
sensitive zone or interface identifiers, such identifiers including
upper case letters cannot be used in the host component of a URI,
because they will be incorrectly converted to lower case.
We now present the corresponding formal syntax.
The URI syntax specification in RFC 3986 formally defines the IPv6
literal format in ABNF [RFC5234] by the following rule:
IP-literal = "[" ( IPv6address / IPvFuture ) "]"
To provide support for a zone identifier, the existing syntax of
IPv6address is retained, and a zone identifier may be added
optionally to any literal address. This syntax allows flexibility
for unknown future uses. The rule quoted above from RFC 3986 is
replaced by four rules:
IP-literal = "[" ( IPv6address / IPv6addrz / IPvFuture ) "]"
ZoneID = 1*( lc-unreserved )
lc-unreserved = %x61-7A / DIGIT / "-" / "." / "_" / "~"
IPv6addrz = IPv6address "%" ZoneID
Note that this change restricts the character set left open by RFC
4007, and because of the lower case issue it restricts the
"unreserved" character set of RFC 3986.
This ABNF change also applies to [RFC3987].
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This syntax fills the gap that is described at the end of
Section 11.7 of the IPv6 Scoped Address Architecture specification
[RFC4007]. It replaces and obsoletes the syntax in Section 2 of
[RFC6874].
The established rules for textual representation of IPv6 addresses
[RFC5952] SHOULD be applied in producing URIs.
RFC 3986 states that URIs have a global scope, but that in some cases
their interpretation depends on the end-user's context. URIs
including a zone identifier are an example of this, since the zone
identifier is of local significance only. Such a zone identifier
cannot be correctly interpreted outside the host to which it applies,
so it must be treated as an opaque string.
When defining zone identifiers compatible with RFC 4007, it is
RECOMMENDED to use only lower case letters, digits, and the symbols
"-", ".", "_" or "~", in order to also be compatible with URI syntax.
In case this recommendation is not adopted, an implementation SHOULD
follow the recommendation in Section 11.2 of RFC 4007 to support
numeric identifiers.
RFC 4007 offers guidance on how the zone identifier affects
interface/address selection inside the IPv6 stack. Note that the
behaviour of an IPv6 stack, if it is passed a non-null zone index for
an address other than link-local, is undefined.
In cases where the RFC 6874 encoding is currently used between
specific software components rather than between a browser and a web
server, such usage MAY continue indefinitely.
4. Scope and Deployment
A URI (or IRI) using this format has no meaning outside the scope of
the individual host that originates it and of the specific layer 2
link concerned. It may in fact be delivered in an HTTP message to a
server that does not support this format and which will reject the
message as invalid. For the diagnostic use cases concerned, this is
of no importance: an HTTP error response will serve the diagnostic
purpose of establishing that the link and remote host are
operational. The other use cases shown above are only meaningful if
the remote host also accepts this format; otherwise they will fail
with an HTTP error response. As a result, this format can be
deployed progressively as required, with no wider consequences.
It is worth noting that there is nothing new about a URI that refers
to a local resource. URIs referring to local domains under ".local"
are normal. Any URI such as "https://169.254.0.1" (link-local IPv4,
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[RFC3927]), "https://10.1.1.1" (private IPv4, [RFC1918]), or
"https://[fd63:45eb:cd14:0:80b2:5c79:62ae:d341]" (IPv6 unique local
address, [RFC4193]) refers to a local resource and has no meaning off
the link or outside the local domain. In operating systems with
support for a default zone identifier, URLs such as
"https://[fe80::2e3a:12cd:fea4:dde7]" already work as expected.
Deployment of support for link-local IPv6 addresses with zone
identifiers introduces no new principle compared to these currently
operational examples.
There has been considerable concern about potential security concerns
caused by locally scoped URIs. A recent W3C Community Group draft
report [PNA-REP] provides background on the issue of cross-origin
resource sharing (CORS), a mechanism which "allows a server to
indicate any origins (domain, scheme, or port) other than its own
from which a browser should permit loading resources." This
mechanism was originally devised for the case of private IPv4
addresses, but has been expanded to cover other cases, explicitly
including link-local IPv6 addresses. Addresses are sorted into three
scopes: loopback, local and public. It could be argued that link-
local addresses which include a zone identifier should be treated on
the same basis as a loopback address, since they are meaningless
outside the originating host (see Section 11.2 of [RFC4007]). In any
case, link-local addresses can clearly be handled by the CORS
mechanism, regardless of the presence or absence of a zone
identifier. To respect the general prohibition on transmitting zone
identifiers in Section 11.2 of RFC 4007, CORS can ensure that they
are not processed by the receiving node.
5. URI Parsers
This section discusses how URI (or IRI) parsers, such as those
embedded in web browsers, might handle this syntax extension.
In practice, although parsers respect the established syntax, many
are coded pragmatically rather than being formally syntax-driven.
Typically, IP address literals are handled by an explicit code path.
Parsers have been inconsistent in providing for zone identifiers.
Most have no support, but there have been examples of ad hoc support.
For example, some versions of Firefox allowed the use of a zone
identifier preceded by a bare "%" character, but this feature was
removed for consistency with the established syntax of RFC 3986. As
another example, some versions of Internet Explorer allowed use of a
zone identifier preceded by a "%" character encoded as "%25", still
beyond the syntax allowed by the established rules. This syntax
extension is in fact used internally in the Windows operating system
and some of its APIs.
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URI parsers SHOULD accept a zone identifier according to the syntax
defined in Section 3, rather than treating the URI as invalid as they
do today. An IPv6 address literal never contains percent-encodings.
In terms of Section 2.4 of [RFC3986], the "%" character preceding a
zone identifier is acting as a delimiter, not as data. Any code
handling percent-encoding or percent-decoding must be aware of this.
While the ABNF syntax defined above is consistent, there are many
existing URI parsers that apply percent decoding liberally (including
within IPv6 literals) regardless of the ABNF, so the probability of
practical and operational problems is claimed to be very high,
especially during the period when some parsers have been updated and
others have not. For example, the URI "http://[fe80::cd%21]" might
be incorrectly decoded as "http://[fe80::cd!]", which will fail.
However, as discussed in the first paragraph of Section 4, errors of
this type will not prevent progressive deployment of the new syntax
on devices that need it.
As noted above, a zone identifier included in a URI has no meaning
outside the originating HTTP client node. This has two consequences:
1. In some use cases, such as CUPS, the host address embedded in the
URI will be reflected back to the client, using exactly the
representation of the zone identifier that the client sent.
Otherwise, the zone identifier is of no value to the server.
2. A URI parser which is not running in the originating host cannot
verify the validity of the zone identifier, since that is only
possible on the originating host. It can only verify that it
conforms to the ABNF.
The various use cases for the zone identifier syntax will usually
require it to be entered in a browser's input dialogue box. However,
URIs including a zone identifier might occur in HTML documents. For
example, a diagnostic script in an HTML page might be tailored for a
particular host. Because of such usage, it is appropriate for
browsers to treat such URIs in the same way whether they are entered
in the dialogue box or encountered in an HTML document.
6. Security Considerations
The security considerations from the URI syntax specification
[RFC3986] and the IPv6 Scoped Address Architecture specification
[RFC4007] apply. In particular, this URI format creates a specific
pathway by which a deceitful zone index might be communicated, as
mentioned in the final security consideration of the Scoped Address
Architecture specification.
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However, this format is only meaningful for link-local addresses
under prefix fe80::/10. It is not necessary for web browsers to
verify this, or to validate the zone identifier, because the
operating system will do so when the address is passed to the socket
API, and return an error code if the zone identifier is invalid.
This is in addition to the protection offered by CORS when a zone
identifier is transmitted to another device, as discussed in
Section 4.
A zone identifier in a URI will be revealed to the recipient of an
HTTP message containing it (typically in the "Host" field [RFC9110]).
A server that receives a zone identifier in an HTTP message or
otherwise SHOULD NOT make use of it, for validation of authority or
any other purpose, since it has no meaning outside the originating
host. Existing practice for controlling cross-origin resource
sharing applies, as discussed above Section 4.
Visibility of the zone identifier to a server is anyway a minor
security concern, since the information revealed is of local
significance only and will be exploitable only if both the client
host and the server have both already been compromised.
Unfortunately there is no formal limit on the length of the zone
identifier string in RFC 4007. An implementation SHOULD apply a
reasonable length limit when generating a URI, in order to minimize
the risk of a buffer overrun. For example, a limit to 16 ASCII
characters would correspond to the existing limit on Linux interface
names.
An implementation SHOULD NOT include ASCII NULL characters in a zone
identifier string as this could cause inconsistencies in subsequent
string processing.
It is conceivable that this format could be misused to remotely probe
a local network configuration or to fingerprint a host. In
particular, a script included in an HTML web page could originate
HTTP messages intended to determine if a particular link-local
address is valid, for example to discover and misuse the address of
the first-hop router. However, such attacks are already possible, by
probing IPv4 addresses, routeable IPv6 addresses or link-local
addresses without a zone identifier. Indeed, with a zone identifier
present, the attacker's job is harder because they must also guess
the zone identifier itself; the zone identifier increases the search
space compared to guessing only the interface identifier. Zone
identifiers vary widely between operating systems; in some cases they
are easily guessed small integers or conventional names such as
"eth0" but in other cases they contain arbitrary characters derived
from MAC addresses. In any case, an attacker must discover them
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before probing any link-local addresses. This argues against the
recommendation of [RFC4007] to support a default zone identifier.
Nevertheless, the principal defence against scanning attacks remains
the 64 bit size of the IPv6 interface identifier [RFC7707].
In the case that a zone identifier contains the hexadecimal MAC
address of a network interface, it will be revealed to the HTTP
recipient and to any observer on the link. Since the MAC address
will also be visible in the underlying layer 2 frame, this is not a
new exposure. Nevertheless, this method of naming interfaces might
be considered to be a privacy issue.
It should be noted that if a node uses an interface identifier in the
outdated Modified EUI format [RFC4291] for its link-local address,
the search space for an attacker is very significantly reduced, as
discussed in Section 4.1.1.1 of [RFC7707]. The resultant
recommendations of [RFC8064] apply to all nodes, including routers,
since they ensure that the search space for an attacker is of size
2**64, which is impracticably large.
Nevertheless, even a Modified EUI link-local address is significantly
harder to guess than typical IPv4 addresses for devices such as home
routers, which are often included in published documentation.
7. IANA Considerations
This document makes no request of IANA.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, DOI 10.17487/RFC3987,
January 2005, <https://www.rfc-editor.org/info/rfc3987>.
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[RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
DOI 10.17487/RFC4007, March 2005,
<https://www.rfc-editor.org/info/rfc4007>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952,
DOI 10.17487/RFC5952, August 2010,
<https://www.rfc-editor.org/info/rfc5952>.
[RFC8064] Gont, F., Cooper, A., Thaler, D., and W. Liu,
"Recommendation on Stable IPv6 Interface Identifiers",
RFC 8064, DOI 10.17487/RFC8064, February 2017,
<https://www.rfc-editor.org/info/rfc8064>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
8.2. Informative References
[CUPS] Apple, "Apple CUPS", 2022, <https://www.cups.org/>.
[LITERAL-ZONE]
Fenner, B. and M. Dürst, "Formats for IPv6 Scope Zone
Identifiers in Literal Address Formats", Work in Progress,
October 2005.
[LL-HACK] Jin, P., "Snippets: IPv6 link local connect hack", 2021,
<https://website.peterjin.org/wiki/
Snippets:IPv6_link_local_connect_hack>.
[ONE-NET] NMEA, "The OneNet Standard for IP Networking of Marine
Electronic Devices", 2023,
<https://www.nmea.org/nmea-onenet.html>.
[OP-CUPS] Sweet, M., "OpenPrinting CUPS", 2022,
<https://openprinting.github.io/cups/>.
[PNA-REP] Rigoudy, T., Ed., "Private Network Access", 2023,
<https://wicg.github.io/private-network-access/>.
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[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
J., and E. Lear, "Address Allocation for Private
Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
February 1996, <https://www.rfc-editor.org/info/rfc1918>.
[RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group
MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000,
<https://www.rfc-editor.org/info/rfc2863>.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6",
RFC 3493, DOI 10.17487/RFC3493, February 2003,
<https://www.rfc-editor.org/info/rfc3493>.
[RFC3510] Herriot, R. and I. McDonald, "Internet Printing
Protocol/1.1: IPP URL Scheme", RFC 3510,
DOI 10.17487/RFC3510, April 2003,
<https://www.rfc-editor.org/info/rfc3510>.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927,
DOI 10.17487/RFC3927, May 2005,
<https://www.rfc-editor.org/info/rfc3927>.
[RFC4001] Daniele, M., Haberman, B., Routhier, S., and J.
Schoenwaelder, "Textual Conventions for Internet Network
Addresses", RFC 4001, DOI 10.17487/RFC4001, February 2005,
<https://www.rfc-editor.org/info/rfc4001>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC6874] Carpenter, B., Cheshire, S., and R. Hinden, "Representing
IPv6 Zone Identifiers in Address Literals and Uniform
Resource Identifiers", RFC 6874, DOI 10.17487/RFC6874,
February 2013, <https://www.rfc-editor.org/info/rfc6874>.
[RFC7472] McDonald, I. and M. Sweet, "Internet Printing Protocol
(IPP) over HTTPS Transport Binding and the 'ipps' URI
Scheme", RFC 7472, DOI 10.17487/RFC7472, March 2015,
<https://www.rfc-editor.org/info/rfc7472>.
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[RFC7707] Gont, F. and T. Chown, "Network Reconnaissance in IPv6
Networks", RFC 7707, DOI 10.17487/RFC7707, March 2016,
<https://www.rfc-editor.org/info/rfc7707>.
[RFC8343] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
<https://www.rfc-editor.org/info/rfc8343>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/info/rfc9110>.
Appendix A. Options Considered
The syntax defined above allows a zone identifier to be added to any
IPv6 address. The 6man WG discussed and rejected an alternative in
which the existing syntax of IPv6address would be extended by an
option to add the zone identifier only for the case of link-local
addresses. It was felt that the solution presented in this document
offers more flexibility for future uses and is more straightforward
to implement.
The various syntax options considered are now briefly described.
1. Leave the problem unsolved.
This would mean that per-interface diagnostics would still have
to be performed using ping or ping6:
ping fe80::abcd%en1
Advantage: works today.
Disadvantage: less convenient than using a browser. Leaves use
cases unsatisfied.
2. Simply use the percent character:
http://[fe80::abcd%en1]
Advantage: allows use of browser; allows cut and paste.
Disadvantage: requires code changes to all URI parsers, some of
which differ in their interpretation of the percent-encoding
rules.
This is the option chosen for standardisation.
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3. Use an alternative separator:
http://[fe80::abcd-en1]
Advantage: allows use of browser; simple syntax.
Disadvantages: requires code changes to all URI parsers; requires
manual editing during cut and paste; inconsistent with existing
tools and practice.
Note: The initial proposal for this choice was to use an
underscore as the separator, but it was noted that this may
become invisible or unclear when a user interface automatically
underlines URLs.
4. Simply use the "IPvFuture" syntax left open in RFC 3986:
http://[v6.fe80::abcd-en1]
Advantage: allows use of browser.
Disadvantage: ugly and redundant; doesn't allow simple cut and
paste.
5. Retain the percent character already specified for introducing
zone identifiers for IPv6 Scoped Addresses [RFC4007], and then
percent-encode it when it appears in a URI, according to the
already-established URI syntax rules [RFC3986]:
http://[fe80::abcd%25en1]
Advantage: allows use of browser; consistent with general URI
syntax.
Disadvantages: somewhat ugly and confusing; requires manual
editing during cut and paste; requires code changes to all URI
parsers, some of which differ in their interpretation of the
percent-encoding rules.
Appendix B. Change log
This section is to be removed before publishing as an RFC.
* draft-ietf-6man-rfc6874bis-09, 2023-07-02:
- Noted scope is limited to RFC 4007 model.
- Updated W3C reference.
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* draft-ietf-6man-rfc6874bis-08, 2023-04-06:
- Noted minor inconsistency with RFC 4007.
* draft-ietf-6man-rfc6874bis-07, 2023-04-12:
- Clarified character set restrictions and the applicability of
numeric identifiers as a work-around.
- Updated ABNF to require lower case, reorganized text as a
result.
- Expanded text on handling of zone ID at server.
- Other nits.
* draft-ietf-6man-rfc6874bis-06, 2023-04-07:
- Noted potential exposure of MAC addresses in zone IDs.
- Expanded detail on lower-case normalization.
- Added specific use case examples.
- Added NMEA use case.
- Clearly explained cut-and-paste requirement.
- Indicated that network infrastructure devices are out of scope.
- Noted the work-around using interface numbers.
- Mentioned .local as another case of locally significant URIs.
- Added discussion of CORS.
- Update descriptions of rejected alternatives
- Noted parsing fragility re % sign.
- Other IESG review nits.
* draft-ietf-6man-rfc6874bis-05, 2022-11-07:
- Noted lower case issue.
* draft-ietf-6man-rfc6874bis-04, 2022-10-19:
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- should accept -> SHOULD.
- Suggested maximum length of zone ID.
* draft-ietf-6man-rfc6874bis-03, 2022-09-30:
- Strengthened motivation for publishing this requirement now.
- Removed unnecessary sentence about browsers.
- Noted that zone ID will be revealed to HTTP server.
- Noted that servers should make no use of received zone IDs.
- Noted that zone IDs have no length limit.
- Added section on scope and deployment, specifically noting that
URIs with local scope are nothing new.
- Other Last Call clarifications and nits.
* draft-ietf-6man-rfc6874bis-02, 2022-07-05:
- Improve discussion of URLs in HTML documents
- Discuss scripting attack and Modified EUI IIDs
- Several editorial clarifications
- Some nits fixed
* draft-ietf-6man-rfc6874bis-01, 2022-04-07:
- Extended use cases
- Clarified relationship with RFC3986 language
- Allow for legacy use of RFC6874 format
- Augmented security considerations
- Editorial and reference improvements
* draft-ietf-6man-rfc6874bis-00, 2022-03-19:
- WG adoption
- Clarified security considerations
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* draft-carpenter-6man-rfc6874bis-03, 2022-02-08:
- Changed to bare % signs.
- Added IRIs, RFC3987
- Editorial fixes
* draft-carpenter-6man-rfc6874bis-02, 2021-18-12:
- Give details of open issues
- Update authorship
- Editorial fixes
* draft-carpenter-6man-rfc6874bis-01, 2021-07-11:
- Added section on issues with RFC6874
- Removed suggested heuristic for bare % signs
- Editorial fixes
* draft-carpenter-6man-rfc6874bis-00, 2021-07-05:
- Initial version
Appendix C. Acknowledgements
The lack of this format was first pointed out by Margaret Wasserman
and later by Kerry Lynn. A previous draft document by Bill Fenner
and Martin Dürst [LITERAL-ZONE] discussed this topic but was not
finalised. Michael Sweet and Andrew Cady explained some of the
difficulties caused by RFC 6874. The ABNF syntax proposed above was
drafted by Andrew Cady.
Valuable comments and contributions were made by Karl Auer, Carlos
Bernardos, Carsten Bormann, Benoit Claise, Martin Dürst, David
Farmer, Stephen Farrell, Brian Haberman, Ted Hardie, Philip Homburg,
Tatuya Jinmei, Leif Johansson, Nate Karstens, Yves Lafon, Barry
Leiba, Ted Lemon, Ben Maddison, Radia Perlman, Tom Petch, Michael
Richardson, Tomoyuki Sahara, Jürgen Schönwälder, Nico Schottelius,
Dave Thaler, Martin Thomson, Philipp S. Tiesel, Ole Troan, Éric
Vyncke, Shang Ye, several IESG members, and others.
Authors' Addresses
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Brian Carpenter
School of Computer Science
University of Auckland
PB 92019
Auckland 1142
New Zealand
Email: brian.e.carpenter@gmail.com
Stuart Cheshire
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
United States of America
Email: cheshire@apple.com
Robert M. Hinden
Check Point Software
959 Skyway Road
San Carlos, CA 94070
United States of America
Email: bob.hinden@gmail.com
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