Internet DRAFT - draft-faltstrom-uri
draft-faltstrom-uri
Network Working Group P. Faltstrom
Internet-Draft Netnod
Intended status: Informational O. Kolkman
Expires: September 26, 2015 ISOC
March 25, 2015
The Uniform Resource Identifier (URI) DNS Resource Record
draft-faltstrom-uri-14
Abstract
This document describes the already registered DNS resource record
type called the Uniform Resource Identifier (URI) RR, for publishing
mappings from hostnames to URIs.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 26, 2015.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Applicability Statement . . . . . . . . . . . . . . . . . . . 3
3. DNS considerations . . . . . . . . . . . . . . . . . . . . . 3
4. The format of the URI RR . . . . . . . . . . . . . . . . . . 4
4.1. Ownername, class and type . . . . . . . . . . . . . . . . 4
4.2. Priority . . . . . . . . . . . . . . . . . . . . . . . . 5
4.3. Weight . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.4. Target . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.5. URI RDATA Wire Format . . . . . . . . . . . . . . . . . . 5
5. Usages . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Example: FTP server in the example.com domain . . . . . . 6
5.2. Relation to S-NAPTR . . . . . . . . . . . . . . . . . . . 6
5.3. Relation to U-NAPTR . . . . . . . . . . . . . . . . . . . 7
5.4. Relation to SRV . . . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6.1. Registration of the URI Resource Record Type . . . . . . 7
6.2. Registration of services . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Non-normative references . . . . . . . . . . . . . . . . 9
Appendix A. The original RRTYPE Allocation Request . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
This document explains the use of the Domain Name System (DNS) for
the storage of URIs [RFC3986], and how to resolve hostnames to such
URIs that can be used by various applications using the URI Resource
Record Type. For resolution the application need to know both the
hostname and the protocol that the URI is to be used for. The
protocol is registered by IANA.
Historically, uses of the DNS to map a domain name to a URL have
relied on the NAPTR RRTYPEs and then on the DDDS [RFC3401]
application framework with the DNS as a database as specified in RFC
3404 [RFC3404]. This has a number of implications such as the fact
the RRSet returned will contain all URIs "connected" with the owner,
and not only the ones related to a specific service.
The URI resource record specified in this document enables the
querying party to do the equivalence of selecting which ones of the
NAPTR records one is interested in, and have only those returned.
This because data in the service field of the NAPTR record is
included in the owner part of the URI resource record type. It is
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also the case that as the URI resource record type include the target
URI directly as part of the RDATA, it is very easy to extract the
correct target URI, instead of applying rewrite rules as in NAPTR.
Querying for URI resource records is not replacing querying for NAPTR
resource records (or use of S-NAPTR [RFC3958]). Instead, the URI
resource record type provides a complementary mechanism to use when
one already knows what service field is interesting. With it, one
can directly query for the specific subset of the otherwise possibly
large RRSet given back when querying for NAPTR resource records.
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 in BCP 14, RFC 2119
[RFC2119].
2. Applicability Statement
In general, it is expected that URI records will be used by clients
for applications where the relevant protocol to be used is known,
but, for example, an extra abstraction is needed in order to separate
a domain name from a point of service (as addressed by the URI). One
example of such a situation is when an organisation has many domain
names, but only one official web page.
Applications MUST know the specific service to prepend the hostname
with. Using repetitive queries for URI records MUST NOT be a
replacement for querying for NAPTR records according to the NAPTR
(DDDS) or S-NAPTR algorithms. NAPTR records serve the purpose to
discover the various services and URIs for looking up access points
for a given service. Those are two very different kinds of needs.
3. DNS considerations
Using prefix labels, such as underscored service tags, for a specific
owner name may cause a counter-intuitive effect when the owner name
is a wildcard name. For example, _s2._s1.*.example.net. is not a
wildcard name and cannot be used to return a synthesized answer for a
query name of _s2._s1.a.example.net. See Section 4.5 of RFC4592
[RFC4592] for more details. Besides, underscored service tags used
for the URI RR (based on the Service Name and Transport Protocol Port
Number Registry) may have slightly different semantics than service
tags used for underscored prefix labels that are used in combination
with other (yet unspecified) RR types. This may cause subtle
management problems when delegation structure that has developed
within the context of URI RRs is also to be used for other RR types.
Since the service labels might be overloaded, applications should
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carefully check that the application level protocol is indeed the
protocol they expect.
Subtle management issues may also arise when the delegations from
service to sub service label involves several parties and different
stake holders.
4. The format of the URI RR
This is the presentation format of the URI RR:
Ownername TTL Class URI Priority Weight Target
The URI RR does not cause any kind of Additional Section processing.
4.1. Ownername, class and type
The URI ownername is subject to special conventions.
Just like the SRV RR [RFC2782] the URI RR has service information
encoded in its ownername. In order to encode the service for a
specific owner name one uses service parameters. Valid service
parameters used are those registered by IANA in the Service Name and
Transport Protocol Port Number Registry [RFC6335], or as Enumservice
Registrations [RFC6117]. The Enumservice Registration parameters are
reversed (subtype(s) before type), prepended with an underscore (_)
and prepended to the owner name in separate labels. The underscore
is prepended to the service parameters to avoid collisions with DNS
labels that occur in nature, and the order is reversed to make it
possible to do delegations, if needed, to different zones (and
therefore providers of DNS).
For example, suppose we are looking for the URI for a service with
ENUM Service Parameter "A:B:C" for host example.com. Then we would
query for (QNAME,QTYPE)=("_C._B._A.example.com","URI")
As another example, suppose we are looking for the URI for a service
with Service Name "A" and Transport Protocol "B" for host
example.com. Then we would query for
(QNAME,QTYPE)=("_A._B.example.com","URI")
The type number for the URI record is 256.
The URI resource record is class independent.
The URI RR has no special TTL requirements.
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4.2. Priority
The priority of the target URI in this RR. Its range is 0-65535. A
client MUST attempt to contact the URI with the lowest-numbered
priority it can reach; URIs with the same priority SHOULD be selected
according to propabilities defined by the weight field.
4.3. Weight
A server selection mechanism. The weight field specifies a relative
weight for entries with the same priority. Larger weights SHOULD be
given a proportionately higher probability of being selected. The
range of this number is 0-65535.
4.4. Target
The URI of the target, enclosed in double-quote characters ('"'),
where the URI is as specified in RFC 3986 [RFC3986]. Resolution of
the URI is according to the definitions for the Scheme of the URI.
Since the URI will not be encoded as a <character-string> (see
RFC1035 section 3.3 [RFC1035]) there is no 255 character size
limitation.
The Target MUST NOT be an empty URI ("").
4.5. URI RDATA Wire Format
The RDATA for a URI RR consists of a 2 octet Priority field, a two
octet Weight field, and a variable length target field.
Priority and Weight are unsigned integers in network byte order.
The remaining data in the RDATA contains the Target field. The
Target field contains the URI as a sequence of octets (without the
enclosing double- quote characters used in the presentation format).
The length of the target field MUST be greater than zero.
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1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ /
/ Target /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5. Usages
5.1. Example: FTP server in the example.com domain
An organisation has the domain names example.com and example.net, and
their FTP archive is at ftp://ftp1.example.com/public. Given the
Service Name "ftp" and Transport Protocol "tcp" (from the IANA
registry of Service Name and Transport Protocol Port Numbers), the
following URI Resource Records could be made available in the
respective zones (example.com and example.net):
$ORIGIN example.com.
_ftp._tcp IN URI 10 1 "ftp://ftp1.example.com/public"
$ORIGIN example.net.
_ftp._tcp IN URI 10 1 "ftp://ftp1.example.com/public"
5.2. Relation to S-NAPTR
The URI resource record type is not a replacement for the S-NAPTR.
It is instead an extension and the second step of the S-NAPTR
resolution can resolve a URI resource record instead of using SRV
records and yet another algorithm for how to use SRV records for the
specific protocol.
$ORIGIN example.com.
;; order pref flags
IN NAPTR 100 10 "D" "EM:ProtA" ( ; service
"" ; regexp
_http._tcp.example.com. ; replacement
_http._tcp IN URI 10 1 "http://www.example.com/path"
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5.3. Relation to U-NAPTR
The URI Resource Record Type, together with S-NAPTR, can be viewed as
a replacement for U-NAPTR [RFC4848]. The URI Resource Record Type is
though only interesting when one know a base domain name, a protocol
and service so that one can compose the record to look up. NAPTR
records of any kind are used to look up what services exists for a
certain domain, which is one step before the URI resource record is
used.
5.4. Relation to SRV
The URI Resource Record Type can be viewed as a replacement for the
SRV record. This because it like the SRV record can only be looked
up if one know the base domain, the protocol and the service. It has
a similar functionality, and uses the same registry for Service
Names, but instead of returning a hostname and port number, the URI
record return a full URI. As such, it can be viewed as a more
powerful resource record than SRV.
6. IANA Considerations
6.1. Registration of the URI Resource Record Type
After an expert review in February 2011 (see Appendix A) IANA has
allocated RRTYPE 256 for the URI Resource Record Type in the registry
named Resource Record (RR) TYPEs and QTYPEs as defined in BCP 42 (at
the time RFC 6195 [RFC6195]), located at
http://www.iana.org/assignments/dns-parameters.
IANA is requested to update the reference with that registration to
this RFC.
6.2. Registration of services
No new registry is needed for the registration of services as the
Service Name, Transport Protocol Port Numbers, Enumservices and the
DNS SRV Service Type registries are used also for the URI resource
record type.
7. Security Considerations
Using the URI resource record together with security mechanisms that
relies on verification of authentication of hostnames, like TLS,
makes it important to choose the correct domain name when doing the
comparison, and that the change in what hostname to use is secured by
DNSSEC so that it can be trusted in a similar way as a redirect in
HTTP using TLS.
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If for example the URI resource record is not signed with the help of
DNSSEC, and then validated successfully, trusting the non-signed URI
will effectlyely lead to a downgrade attack.
The basic mechanism for successful use of URI works as follows:
1. Announce the fact example.com is hosted at example.org (with
some URL) in DNS
2. Secure the URI resource record with DNSSEC. Best of course by
doing validation in the application doing the lookup, but it
could also be in the local recursive resolver or in the trusted
recursive resolver also doing validation. All according to the
local trust policy.
3. Verify the TLS (for example) certificate for the connection to
example.org matches, i.e. use the hostname in the URI and not
the hostname used originally when looking up the URI resource
record.
4. If needed, do application layer authentication etc over the then
encrypted connection.
What also can happen is that the URI in the resource record type has
errors in it. Applications using the URI resource record type for
resolution should behave similarly as if the user typed (or copy and
pasted) the URI. At least it must be clear to the user that the
error is not due to any error from his side.
One SHOULD NOT include userinfo (see User Information, Section 3.2.1,
in RFC 3986 [RFC3986]) in a URI that is used in a URI resource record
as DNS data must be viewed as publicly available information.
8. Acknowledgements
Ideas on how to split the two different kind of queries "What
services exists for this domain name" and "What is the URI for this
service" came from Scott Bradner and Lawrence Conroy. Other people
that have contributed to this document include Richard Barnes, Leslie
Daigle, Victor Dukhovni, Olafur Gudmundsson, Philip Hallam-Baker, Ted
Hardie, Sam Hartman, Evan Hunt, John klensin, Peter Koch, Eliot Lear,
Andy Newton, Mark Nottingham, Penn Pfautz, Jinmei Tatuya, Willem
Toorop, Nico Williams.
Cisco is acknowledged as mr Faltstrom's employer at the time this
document was developed.
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The NLnet Labs is acknowledged as mr Kolkman's employer at the time
this document was developed.
9. References
9.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, January 2005.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
[RFC6117] Hoeneisen, B., Mayrhofer, A., and J. Livingood, "IANA
Registration of Enumservices: Guide, Template, and IANA
Considerations", RFC 6117, March 2011.
[RFC6195] Eastlake, D., "Domain Name System (DNS) IANA
Considerations", RFC 6195, March 2011.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165, RFC
6335, August 2011.
9.2. Non-normative references
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC3401] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
Part One: The Comprehensive DDDS", RFC 3401, October 2002.
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[RFC3403] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
Part Three: The Domain Name System (DNS) Database", RFC
3403, October 2002.
[RFC3404] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
Part Four: The Uniform Resource Identifiers (URI)", RFC
3404, October 2002.
[RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record
(RR) Types", RFC 3597, September 2003.
[RFC3833] Atkins, D. and R. Austein, "Threat Analysis of the Domain
Name System (DNS)", RFC 3833, August 2004.
[RFC3958] Daigle, L. and A. Newton, "Domain-Based Application
Service Location Using SRV RRs and the Dynamic Delegation
Discovery Service (DDDS)", RFC 3958, January 2005.
[RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name
System", RFC 4592, July 2006.
[RFC4848] Daigle, L., "Domain-Based Application Service Location
Using URIs and the Dynamic Delegation Discovery Service
(DDDS)", RFC 4848, April 2007.
[RFC5507] IAB, Faltstrom, P., Austein, R., and P. Koch, "Design
Choices When Expanding the DNS", RFC 5507, April 2009.
Appendix A. The original RRTYPE Allocation Request
On February 22, 2011 IANA assigned RRTYPE 256 for the URI resource
record based on a request that followed the procedure documented in
RFC 6195 [RFC6195]. The DNS RRTYPE PARAMETER ALLOCATION form as
submitted to IANA at thet time is replicated below for reference.
A. Submission Date:
May 23, 2009
B. Submission Type:
[X] New RRTYPE
[ ] Modification to existing RRTYPE
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C. Contact Information for submitter:
Name: Patrik Faltstrom
Email Address: paf@cisco.com
International telephone number: +46-8-6859131
Other contact handles:
(Note: This information will be publicly posted.)
D. Motivation for the new RRTYPE application?
There is no easy way to get from a domain name to a URI (or
IRI). Some mechanisms exists via use of the NAPTR [RFC3403]
resource record. That implies quite complicated rules that are
simplified via the S-NAPTR [RFC3958] specification. But, the
ability to directly look up a URI still exists. This
specification uses a prefix based naming mechanism originated in
the definition of the SRV [RFC2782] resource record, and the
RDATA is a URI, encoded as one text field.
See also above (Section 1).
E. Description of the proposed RR type.
The format of the URI resource record is as follows:
Ownername TTL Class URI Priority Weight Target
The URI RR has service information encoded in its ownername. In
order to encode the service for a specific owner name one uses
service parameters. Valid service parameters used are either
Enumservice Registrations registered by IANA, or prefixes used
for the SRV resource record.
The wire format of the RDATA is as follows:
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1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ /
/ Target /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
F. What existing RRTYPE or RRTYPEs come closest to filling that
need and why are they unsatisfactory?
The RRTYPE that come closest is the NAPTR resource record. It
is for example used in the DDDS and S-NAPTR algorithms. The
main problem with the NAPTR is that selection of what record (or
records) one is interested in is based on data stored in the
RDATA portion of the NAPTR resource record. This, as explained
in RFC 5507 [RFC5507], is not optimal for DNS lookups. Further,
most applications using NAPTR resource records uses regular
expression based rewrite rules for creation of the URI, and that
has shown be complicated to implement.
The second closest RRTYPE is the SRV record that given a
prefixed based naming just like is suggested for the URI
resource record, one get back a port number and domain name.
This can also be used for creation of a URI, but, only URIs
without path components.
G. What mnemonic is requested for the new RRTYPE (optional)?
URI
H. Does the requested RRTYPE make use of any existing IANA Registry
or require the creation of a new IANA sub-registry in DNS
Parameters?
Yes, partially.
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One of the mechanisms to select a service is to use the
Enumservice Registry managed by IANA. Another is to use
services and protocols used for SRV records.
I. Does the proposal require/expect any changes in DNS servers/
resolvers that prevent the new type from being processed as an
unknown RRTYPE (see RFC 3597 [RFC3597])?
No
J. Comments:
None
Authors' Addresses
Patrik Faltstrom
Netnod
Email: paf@netnod.se
Olaf Kolkman
Internet Society
Email: kolkman@isoc.org
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