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BEST CURRENT PRACTICE
Internet Engineering Task Force (IETF) D. Crocker
Request for Comments: 8553 Brandenburg InternetWorking
BCP: 222 March 2019
Updates: 2782, 3263, 3529, 3620, 3832,
3887, 3958, 4120, 4227, 4386,
4387, 4976, 5026, 5328, 5389,
5415, 5518, 5555, 5617, 5679,
5766, 5780, 5804, 5864, 5928,
6120, 6186, 6376, 6733, 6763,
7208, 7489, 8145
Category: Best Current Practice
ISSN: 2070-1721
DNS AttrLeaf Changes:
Fixing Specifications That Use Underscored Node Names
Abstract
Using an underscore for a prefix creates a space for constrained
interoperation of resource records. Original uses of an underscore
character as a domain node name prefix were specified without the
benefit of an IANA registry. This produced an entirely uncoordinated
set of name-creation activities, all drawing from the same namespace.
A registry for these names has now been defined by RFC 8552.
However, the existing specifications that use underscored naming need
to be modified in order to be in line with the new registry. This
document specifies those changes. The changes preserve existing
software and operational practice, while adapting the specifications
for those practices to the newer underscore registry model.
Status of This Memo
This memo documents an Internet Best Current Practice.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8553.
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Copyright Notice
Copyright (c) 2019 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 Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Underscored RRset Use in Specifications . . . . . . . . . . . 3
2.1. TXT RRset . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. SRV RRset . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. URI RRset . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Underscored Template Specifications . . . . . . . . . . . . . 7
3.1. SRV Specification Changes . . . . . . . . . . . . . . . . 7
3.2. URI Specification Changes . . . . . . . . . . . . . . . . 8
3.3. DNSSEC Signaling Specification Changes . . . . . . . . . 10
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Normative References . . . . . . . . . . . . . . . . . . 11
6.2. Informative References . . . . . . . . . . . . . . . . . 12
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
Original uses of an underscore character as a domain node name
[RFC1035] prefix, which creates a space for constrained
interpretation of resource records, were specified without the
benefit of an IANA registry [IANA-reg]. This produced an entirely
uncoordinated set of name-creation activities, all drawing from the
same namespace. A registry has now been defined (see Section 4 of
[RFC8552]); the RFC that defined it discusses the background for the
use of underscored domain names [RFC8552].
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The basic model for underscored name registration, as specified in
[RFC8552], is to have each registry entry be unique in terms of the
combination of a resource record type and a "global" (highest-level)
underscored node name; that is, the node name beginning with an
underscore that is the closest to the DNS root.
The specifications describing the existing uses of underscored naming
do not reflect the existence of this integrated registry. For the
new reader or the new editor of one of those documents, there is
currently nothing signaling that the underscored name(s) defined in
the document are now processed through an IANA registry. This
document remedies that, by marking such a published document with an
update that indicates the nature of the change.
Further, the documents that define the SRV [RFC2782] and URI
[RFC7553] DNS resource records provide a meta-template for
underscored name assignments, partially based on separate registries
[RFC6335]. For the portion that selects the global (highest-level)
underscored node name, this perpetuates uncoordinated assignment
activities by separate technical specifications, out of the same
namespace. This document remedies that by providing detail for
revisions to the SRV and URI specifications to bring their use in
line with the single, integrated "Underscored and Globally Scoped DNS
Node Names" registry.
The result of these changes preserves existing software and
operations practices while adapting the technical specifications to
the newer underscore registry model.
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. Underscored RRset Use in Specifications
The use of underscored node names is specific to each RR TYPE that is
being scoped. Each name defines a place but does not define the
rules for what appears underneath that place, either as additional
underscored naming or as a leaf node with resource records. Details
for those rules are provided by specifications for individual RR
TYPEs. The sections below describe the way that existing underscored
names are used with the RR TYPEs that they name.
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2.1. TXT RRset
NOTE - Documents falling into this category include: [RFC5518],
[RFC5617], [RFC6120], [RFC6376], [RFC6763], [RFC7208], and
[RFC7489].
This section provides a generic approach for changes to existing
specifications that define straightforward use of underscored node
names when scoping the use of a TXT RRset. The approach provides the
information needed for adapting such specifications to the use of the
IANA "Underscored and Globally Scoped DNS Node Names" registry
[RFC8552]. Hence, the approach is meant both as an update to these
existing specifications and as guidance for changes when those
documents are revised.
For any document that specifies the use of a TXT RRset under one or
more underscored names, the global node name is expected to be
registered in the IANA "Underscored and Globally Scoped DNS Node
Names" registry [RFC8552]. An effort has been made to locate
existing documents that do this, to register the global underscored
node names, and to list them in the initial set of names added to the
registry.
If a public specification defines use of a TXT RRset and calls for
the use of an underscored node name, here is a template of suggested
text for registering the global underscored node name -- the one
closest to the root -- that can be used through the IANA
Considerations section of the specification:
"Per [RFC8552], please add the following entry to the "Underscored
and Globally Scoped DNS Node Names" registry:"
+--------+----------------+-----------------------------------------+
| RR | _NODE NAME | Reference |
| Type | | |
+--------+----------------+-----------------------------------------+
| TXT | _{DNS node | {citation for the document making the |
| | name} | addition} |
+--------+----------------+-----------------------------------------+
Table 1: Entry for the "Underscored and Globally Scoped DNS
Node Names" Registry for TXT RR Use
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2.2. SRV RRset
NOTE - Documents falling into this category include:
[RFC3263], [RFC3529], [RFC3620], [RFC3832], [RFC3887],
[RFC3958], [RFC4120], [RFC4227], [RFC4386], [RFC4387],
[RFC4976], [RFC5026], [RFC5328], [RFC5389], [RFC5415],
[RFC5555], [RFC5679], [RFC5766], [RFC5780], [RFC5804],
[RFC5864], [RFC5928], and [RFC6186].
Specification of the SRV resource record [RFC2782] provides a
template for use of underscored node names. The global node name is
characterized as referencing the 'protocol' that is associated with
SRV RRset usage.
This section provides a generic approach for changes to existing
specifications that define the use of an SRV RRset. The approach
provides the information needed for adapting such specifications to
the use of the IANA "Underscored and Globally Scoped DNS Node Names"
registry [RFC8552]. Hence, the approach is meant both as an update
to these existing specifications and as guidance for changes when
those documents are revised.
For any document that specifies the use of an SRV RRset, the global
('protocol') underscored node name is expected to be registered in
the IANA "Underscored and Globally Scoped DNS Node Names" registry
[RFC8552]. An effort has been made to locate existing documents that
do this, to register the global underscored node names, and to list
them in the initial set of names added to the registry.
If a public specification defines use of an SRV RRset and calls for
the use of an underscored node name, here is a template of suggested
text for registering the global underscored node name -- the one
closest to the root -- that can be used through the IANA
Considerations section of the specification:
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"Per [RFC8552], please add the following entry to the "Underscored
and Globally Scoped DNS Node Names" registry:
+--------+----------------------+-----------------------------------+
| RR | _NODE NAME | Reference |
| Type | | |
+--------+----------------------+-----------------------------------+
| SRV | _{DNS 'protocol' | {citation for the document making |
| | node name} | the addition} |
+--------+----------------------+-----------------------------------+
Table 2: Entry for the "Underscored and Globally Scoped DNS Node
Names" Registry for SRV RR Use
2.3. URI RRset
Specification of the URI resource record [RFC7553] provides a
template for use of underscored node names. The global node name is
characterized as naming the 'protocol' that is associated with URI RR
usage or by reversing an Enumservice sequence [RFC6117].
This section provides a generic approach for changes to existing
specifications that define use of a URI RRset. The approach provides
the information needed for adapting such specifications to the use of
the IANA "Underscored and Globally Scoped DNS Node Names" registry
[RFC8552]. Hence, the approach is meant both as an update to these
existing specifications and as guidance for changes when those
documents are revised.
For any document that specifies the use of a URI RRset, the global
('protocol' or highest-level Enumservice) underscored node name is
expected to be registered in the IANA "Underscored and Globally
Scoped DNS Node Names" registry [RFC8552]. An effort has been made
to locate existing documents that do this, to register the global
underscored node names, and to list them in the initial set of names
added to the registry.
If a public specification defines use of a URI RRset and calls for
the use of an underscored node name, here is a template of suggested
text for registering the global underscored node name -- the one
closest to the root -- that can be used through the IANA
Considerations section of the specification:
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"Per [RFC8552], please add the following entry to the "Underscored
and Globally Scoped DNS Node Names" registry:
+-------+----------------------------+------------------------------+
| RR | _NODE NAME | Reference |
| Type | | |
+-------+----------------------------+------------------------------+
| URI | _{DNS 'protocol' or | {citation for the document |
| | Enumservice node name} | making the addition} |
+-------+----------------------------+------------------------------+
Table 3: Entry for the "Underscored and Globally Scoped DNS Node
Names" Registry for URI RR Use
3. Underscored Template Specifications
3.1. SRV Specification Changes
The specification for a domain name, under which an SRV resource
record [RFC2782] appears, provides a template for use of underscored
node names. The global underscored node name is characterized as
indicating the 'protocol' that is associated with SRV RR usage.
The text of [RFC2782] is changed as described below. In addition,
note that a normative reference to RFC 8552 is added to the
References section of RFC 2782.
OLD:
The format of the SRV RR
Here is the format of the SRV RR, whose DNS type code is 33:
_Service._Proto.Name TTL Class SRV Priority Weight Port Target
...
Proto
The symbolic name of the desired protocol, with an underscore
(_) prepended to prevent collisions with DNS labels that occur
in nature. _TCP and _UDP are at present the most useful values
for this field, though any name defined by Assigned Numbers or
locally may be used (as for Service). The Proto is case
insensitive.
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NEW:
The format of the SRV RR
Here is the format of the SRV RR, whose DNS type code is 33:
"_Service._Proto.Name TTL Class SRV Priority Weight Port
Target"
_..._
Proto
The symbolic name of the desired protocol with an underscore
(e.g., "_name") prepended to prevent collisions with DNS
labels that occur in nature. _TCP and _UDP are at present
the most useful values for this field. The Proto is case
insensitive.
The SRV RRset 'protocol' (global) underscored node name
SHOULD be registered in the IANA "Underscored and Globally
Scoped DNS Node Names" registry [RFC8552].
3.2. URI Specification Changes
Specification for the domain name (under which a URI resource record
[RFC7553] occurs) is similar to that for the SRV resource record
[RFC2782], although the text refers only to 'service' name, rather
than distinguishing 'service' from 'protocol'. Further, the URI RR
specification permits alternative underscored naming schemes:
One matches what is used for SRV, with the global underscored node
name called 'protocol'.
The other is based on a reversing of an Enumservice [RFC6117]
sequence.
Text of [RFC7553] is changed as described below. In addition, a
normative reference to RFC 8552 is added to the References section of
RFC 7553.
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OLD:
4.1. Owner Name, Class, and Type
The URI owner name is subject to special conventions.
Just like the SRV RR [RFC2782], the URI RR has service information
encoded in its owner name. In order to encode the service for a
specific owner name, one uses service parameters. Valid service
parameters 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 (i.e., 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").
NEW:
4.1. Owner Name, Class, and Type
The URI owner name is subject to special conventions.
As for the SRV RRset [RFC2782], the URI RRset global (highest-
level) underscored node name SHOULD be registered in the IANA
"Underscored and Globally Scoped DNS Node Names" registry
[RFC8552].
Just like the SRV RRset, the URI RRset has service information
encoded in its owner name. In order to encode the service for
a specific owner name, one uses service parameters. Valid
service parameters are:
+ Those registered by IANA in the "Service Name and Transport
Protocol Port Number Registry" [RFC6335]. The underscore is
prepended to the service parameters to avoid collisions with
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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).
+ Those listed in "Enumservice Registrations" [RFC6117]. The
Enumservice Registration parameters are reversed (i.e.,
subtype(s) before type), prepended with an underscore (e.g.,
"_name"), and prepended to the owner name in separate
labels. The highest-level (global) underscored Enumservice
name becomes the global name per RFC 8552 to register.
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").
3.3. DNSSEC Signaling Specification Changes
"Signaling Trust Anchor Knowledge in DNS Security Extensions
(DNSSEC)" [RFC8145] defines a use of DNS node names that effectively
consumes all names beginning with the string "_ta-" when using the
NULL RR in the query.
Text of Section 5.1, "Query Format", of RFC 8145 is changed as
described below. In addition, a normative reference to RFC 8552 is
added to the References section of RFC 8145.
OLD:
For example, a validating DNS resolver ...
QNAME=_ta-4444.
NEW:
For example, a validating DNS resolver ... "QNAME=_ta-4444".
Under the NULL RR, an entry is registered in the IANA
"Underscored and Globally Scoped DNS Node Names" registry
[RFC8552] for all node names beginning with "_ta-".
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4. IANA Considerations
Although this document makes reference to IANA registries, it
introduces no new IANA registries or procedures.
5. Security Considerations
This memo raises no security issues.
6. References
6.1. 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>.
[RFC6117] Hoeneisen, B., Mayrhofer, A., and J. Livingood, "IANA
Registration of Enumservices: Guide, Template, and IANA
Considerations", RFC 6117, DOI 10.17487/RFC6117, March
2011, <https://www.rfc-editor.org/info/rfc6117>.
[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, DOI 10.17487/RFC6335, August 2011,
<https://www.rfc-editor.org/info/rfc6335>.
[RFC7553] Faltstrom, P. and O. Kolkman, "The Uniform Resource
Identifier (URI) DNS Resource Record", RFC 7553,
DOI 10.17487/RFC7553, June 2015,
<https://www.rfc-editor.org/info/rfc7553>.
[RFC8145] Wessels, D., Kumari, W., and P. Hoffman, "Signaling Trust
Anchor Knowledge in DNS Security Extensions (DNSSEC)",
RFC 8145, DOI 10.17487/RFC8145, April 2017,
<https://www.rfc-editor.org/info/rfc8145>.
[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>.
[RFC8552] Crocker, D., "Scoped Interpretation of DNS Resource
Records through "Underscored" Naming of Attribute Leaves",
RFC 8552, DOI 10.17487/RFC8552, March 2019,
<https://www.rfc-editor.org/info/rfc8552>.
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6.2. Informative References
[IANA-reg]
IANA, "Protocol Registries",
<https://www.iana.org/protocols>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
DOI 10.17487/RFC2782, February 2000,
<https://www.rfc-editor.org/info/rfc2782>.
[RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation
Protocol (SIP): Locating SIP Servers", RFC 3263,
DOI 10.17487/RFC3263, June 2002,
<https://www.rfc-editor.org/info/rfc3263>.
[RFC3529] Harold, W., "Using Extensible Markup Language-Remote
Procedure Calling (XML-RPC) in Blocks Extensible Exchange
Protocol (BEEP)", RFC 3529, DOI 10.17487/RFC3529, April
2003, <https://www.rfc-editor.org/info/rfc3529>.
[RFC3620] New, D., "The TUNNEL Profile", RFC 3620,
DOI 10.17487/RFC3620, October 2003,
<https://www.rfc-editor.org/info/rfc3620>.
[RFC3832] Zhao, W., Schulzrinne, H., Guttman, E., Bisdikian, C., and
W. Jerome, "Remote Service Discovery in the Service
Location Protocol (SLP) via DNS SRV", RFC 3832,
DOI 10.17487/RFC3832, July 2004,
<https://www.rfc-editor.org/info/rfc3832>.
[RFC3887] Hansen, T., "Message Tracking Query Protocol", RFC 3887,
DOI 10.17487/RFC3887, September 2004,
<https://www.rfc-editor.org/info/rfc3887>.
[RFC3958] Daigle, L. and A. Newton, "Domain-Based Application
Service Location Using SRV RRs and the Dynamic Delegation
Discovery Service (DDDS)", RFC 3958, DOI 10.17487/RFC3958,
January 2005, <https://www.rfc-editor.org/info/rfc3958>.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
DOI 10.17487/RFC4120, July 2005,
<https://www.rfc-editor.org/info/rfc4120>.
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[RFC4227] O'Tuathail, E. and M. Rose, "Using the Simple Object
Access Protocol (SOAP) in Blocks Extensible Exchange
Protocol (BEEP)", RFC 4227, DOI 10.17487/RFC4227, January
2006, <https://www.rfc-editor.org/info/rfc4227>.
[RFC4386] Boeyen, S. and P. Hallam-Baker, "Internet X.509 Public Key
Infrastructure Repository Locator Service", RFC 4386,
DOI 10.17487/RFC4386, February 2006,
<https://www.rfc-editor.org/info/rfc4386>.
[RFC4387] Gutmann, P., Ed., "Internet X.509 Public Key
Infrastructure Operational Protocols: Certificate Store
Access via HTTP", RFC 4387, DOI 10.17487/RFC4387, February
2006, <https://www.rfc-editor.org/info/rfc4387>.
[RFC4976] Jennings, C., Mahy, R., and A. Roach, "Relay Extensions
for the Message Sessions Relay Protocol (MSRP)", RFC 4976,
DOI 10.17487/RFC4976, September 2007,
<https://www.rfc-editor.org/info/rfc4976>.
[RFC5026] Giaretta, G., Ed., Kempf, J., and V. Devarapalli, Ed.,
"Mobile IPv6 Bootstrapping in Split Scenario", RFC 5026,
DOI 10.17487/RFC5026, October 2007,
<https://www.rfc-editor.org/info/rfc5026>.
[RFC5328] Adolf, A. and P. MacAvock, "A Uniform Resource Name (URN)
Namespace for the Digital Video Broadcasting Project
(DVB)", RFC 5328, DOI 10.17487/RFC5328, September 2008,
<https://www.rfc-editor.org/info/rfc5328>.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
DOI 10.17487/RFC5389, October 2008,
<https://www.rfc-editor.org/info/rfc5389>.
[RFC5415] Calhoun, P., Ed., Montemurro, M., Ed., and D. Stanley,
Ed., "Control And Provisioning of Wireless Access Points
(CAPWAP) Protocol Specification", RFC 5415,
DOI 10.17487/RFC5415, March 2009,
<https://www.rfc-editor.org/info/rfc5415>.
[RFC5518] Hoffman, P., Levine, J., and A. Hathcock, "Vouch By
Reference", RFC 5518, DOI 10.17487/RFC5518, April 2009,
<https://www.rfc-editor.org/info/rfc5518>.
[RFC5555] Soliman, H., Ed., "Mobile IPv6 Support for Dual Stack
Hosts and Routers", RFC 5555, DOI 10.17487/RFC5555, June
2009, <https://www.rfc-editor.org/info/rfc5555>.
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[RFC5617] Allman, E., Fenton, J., Delany, M., and J. Levine,
"DomainKeys Identified Mail (DKIM) Author Domain Signing
Practices (ADSP)", RFC 5617, DOI 10.17487/RFC5617, August
2009, <https://www.rfc-editor.org/info/rfc5617>.
[RFC5679] Bajko, G., "Locating IEEE 802.21 Mobility Services Using
DNS", RFC 5679, DOI 10.17487/RFC5679, December 2009,
<https://www.rfc-editor.org/info/rfc5679>.
[RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)", RFC 5766,
DOI 10.17487/RFC5766, April 2010,
<https://www.rfc-editor.org/info/rfc5766>.
[RFC5780] MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery
Using Session Traversal Utilities for NAT (STUN)",
RFC 5780, DOI 10.17487/RFC5780, May 2010,
<https://www.rfc-editor.org/info/rfc5780>.
[RFC5804] Melnikov, A., Ed. and T. Martin, "A Protocol for Remotely
Managing Sieve Scripts", RFC 5804, DOI 10.17487/RFC5804,
July 2010, <https://www.rfc-editor.org/info/rfc5804>.
[RFC5864] Allbery, R., "DNS SRV Resource Records for AFS", RFC 5864,
DOI 10.17487/RFC5864, April 2010,
<https://www.rfc-editor.org/info/rfc5864>.
[RFC5928] Petit-Huguenin, M., "Traversal Using Relays around NAT
(TURN) Resolution Mechanism", RFC 5928,
DOI 10.17487/RFC5928, August 2010,
<https://www.rfc-editor.org/info/rfc5928>.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120,
March 2011, <https://www.rfc-editor.org/info/rfc6120>.
[RFC6186] Daboo, C., "Use of SRV Records for Locating Email
Submission/Access Services", RFC 6186,
DOI 10.17487/RFC6186, March 2011,
<https://www.rfc-editor.org/info/rfc6186>.
[RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
"DomainKeys Identified Mail (DKIM) Signatures", STD 76,
RFC 6376, DOI 10.17487/RFC6376, September 2011,
<https://www.rfc-editor.org/info/rfc6376>.
Crocker Best Current Practice [Page 14]
RFC 8553 DNS AttrLeaf Fix March 2019
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/info/rfc6763>.
[RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for
Authorizing Use of Domains in Email, Version 1", RFC 7208,
DOI 10.17487/RFC7208, April 2014,
<https://www.rfc-editor.org/info/rfc7208>.
[RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
Message Authentication, Reporting, and Conformance
(DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,
<https://www.rfc-editor.org/info/rfc7489>.
Acknowledgements
Thanks go to Bill Fenner, Dick Franks, Tony Hansen, Peter Koch, Olaf
Kolkman, and Andrew Sullivan for diligent review of the (much)
earlier draft versions. For the later enhancements, thanks to Tim
Wicinski, John Levine, Bob Harold, Joel Jaeggli, Ondrej Sury, and
Paul Wouters.
Special thanks to Ray Bellis for his persistent encouragement to
continue this effort, as well as the suggestion for an essential
simplification to the registration model.
Author's Address
Dave Crocker
Brandenburg InternetWorking
675 Spruce Dr.
Sunnyvale, CA 94086
United States of America
Phone: +1.408.246.8253
Email: dcrocker@bbiw.net
URI: http://bbiw.net/
Crocker Best Current Practice [Page 15]
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