Internet Engineering Task Force (IETF) D. Eastlake 3rd
Request for Comments: 6895 Huawei
BCP: 42 April 2013
Updates: 1183, 2845, 2930, 3597
Category: Best Current Practice
Domain Name System (DNS) IANA Considerations
This document specifies Internet Assigned Numbers Authority (IANA)
parameter assignment considerations for the allocation of Domain Name
System (DNS) resource record types, CLASSes, operation codes, error
codes, DNS protocol message header bits, and AFSDB resource record
subtypes. It obsoletes RFC 6195 and updates RFCs 1183, 2845, 2930,
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 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
Copyright (c) 2013 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
(http://trustee.ietf.org/license-info) in effect on the date of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................21.1. Terminology ................................................32. DNS Query/Response Headers ......................................32.1. One Spare Bit? .............................................42.2. OpCode Assignment ..........................................42.3. RCODE Assignment ...........................................43. DNS Resource Records ............................................63.1. RRTYPE IANA Considerations .................................73.1.1. DNS RRTYPE Allocation Policy ........................83.1.2. DNS RRTYPE Expert Guidelines .......................103.1.3. Special Note on the OPT RR .........................103.1.4. The AFSDB RR Subtype Field .........................103.2. RR CLASS IANA Considerations ..............................113.3. Label Considerations ......................................133.3.1. Label Types ........................................133.3.2. Label Contents and Use .............................134. Security Considerations ........................................145. IANA Considerations ............................................14Appendix A. RRTYPE Allocation Template ............................15Appendix B. Changes from RFC 6195 .................................16
Normative References ..............................................17
Informative References ............................................18
Acknowledgements ..................................................191. Introduction
The Domain Name System (DNS) provides replicated distributed secure
hierarchical databases that store "resource records" (RRs) under
domain names. DNS data is structured into CLASSes and zones that can
be independently maintained. Familiarity with [RFC1034], [RFC1035],
[RFC2136], [RFC2181], and [RFC4033] is assumed.
This document provides, either directly or by reference, the general
IANA parameter assignment considerations that apply across DNS query
and response headers and all RRs. There may be additional IANA
considerations that apply to only a particular RRTYPE or
query/response OpCode. See the specific RFC defining that RRTYPE or
query/response OpCode for such considerations if they have been
defined, except for AFSDB RR considerations [RFC1183], which are
included herein. This RFC obsoletes [RFC6195]; however, the only
significant changes are those to the RRTYPE IANA allocation process,
aimed at streamlining it and clarifying the expected behavior of the
parties involved, and the closing of the AFSDB subtype registry.
IANA currently maintains a web page of DNS parameters available from
"Standards Action", "IETF Review", "Specification Required", and
"Private Use" are as defined in [RFC5226].
2. DNS Query/Response Headers
The header for DNS queries and responses contains field/bits in the
following diagram taken from [RFC2136]:
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
| ID |
|QR| OpCode |AA|TC|RD|RA| Z|AD|CD| RCODE |
| QDCOUNT/ZOCOUNT |
| ANCOUNT/PRCOUNT |
| NSCOUNT/UPCOUNT |
| ARCOUNT |
The ID field identifies the query and is echoed in the response so
they can be matched.
The QR bit indicates whether the header is for a query or a response.
The AA, TC, RD, RA, and CD bits are each theoretically meaningful
only in queries or only in responses, depending on the bit. The AD
bit was only meaningful in responses but is expected to have a
separate but related meaning in queries (see Section 5.7 of
[RFC6840]). Only the RD and CD bits are expected to be copied from
the query to the response; however, some DNS implementations copy all
the query header as the initial value of the response header. Thus,
any attempt to use a "query" bit with a different meaning in a
response or to define a query meaning for a "response" bit may be
dangerous, given the existing implementation. Meanings for these
bits may only be assigned by a Standards Action.
The unsigned integer fields query count (QDCOUNT), answer count
(ANCOUNT), authority count (NSCOUNT), and additional information
count (ARCOUNT) express the number of records in each section for all
OpCodes except Update [RFC2136]. These fields have the same
structure and data type for Update but are instead the counts for the
zone (ZOCOUNT), prerequisite (PRCOUNT), update (UPCOUNT), and
additional information (ARCOUNT) sections.
2.1. One Spare Bit?
There have been ancient DNS implementations for which the Z bit being
on in a query meant that only a response from the primary server for
a zone is acceptable. It is believed that current DNS
implementations ignore this bit.
Assigning a meaning to the Z bit requires a Standards Action.
2.2. OpCode Assignment
Currently, DNS OpCodes are assigned as follows:
OpCode Name Reference
0 Query [RFC1035]
1 IQuery (Inverse Query, OBSOLETE) [RFC3425]
2 Status [RFC1035]
4 Notify [RFC1996]
5 Update [RFC2136]
Although the Status OpCode is reserved in [RFC1035], its behavior has
not been specified. New OpCode assignments require a Standards
Action with early allocation permitted as specified in [RFC4020].
2.3. RCODE Assignment
It would appear from the DNS header above that only four bits of
RCODE, or response/error code, are available. However, RCODEs can
appear not only at the top level of a DNS response but also inside
TSIG RRs [RFC2845], TKEY RRs [RFC2930], and extended by OPT RRs
[RFC6891]. The OPT RR provides an 8-bit extension to the 4 header
bits, resulting in a 12-bit RCODE field, and the TSIG and TKEY RRs
have a 16-bit field designated in their RFCs as the "Error" field.
Error codes appearing in the DNS header and in these other RR types
all refer to the same error code space with the exception of error
code 16, which has a different meaning in the OPT RR than in the TSIG
RR, and error code 9, whose variations are described after the table
below. The duplicate assignment of 16 was accidental. To the extent
that any prior RFCs imply any sort of different error number space
for the OPT, TSIG, or TKEY RRs, they are superseded by this unified
DNS error number space. (This paragraph is the reason this document
updates [RFC2845] and [RFC2930].) With the existing exceptions of
error numbers 9 and 16, the same error number must not be assigned
for different errors even if they would only occur in different RR
types. See table below.
RCODE Name Description Reference
0 NoError No Error [RFC1035]
1 FormErr Format Error [RFC1035]
2 ServFail Server Failure [RFC1035]
3 NXDomain Non-Existent Domain [RFC1035]
4 NotImp Not Implemented [RFC1035]
5 Refused Query Refused [RFC1035]
6 YXDomain Name Exists when it should not [RFC2136]
7 YXRRSet RR Set Exists when it should not [RFC2136]
8 NXRRSet RR Set that should exist does not [RFC2136]
9 NotAuth Server Not Authoritative for zone [RFC2136]
9 NotAuth Not Authorized [RFC2845]
10 NotZone Name not contained in zone [RFC2136]
11 - 15
0xB - 0xF Unassigned
16 BADVERS Bad OPT Version [RFC6891]
16 BADSIG TSIG Signature Failure [RFC2845]
17 BADKEY Key not recognized [RFC2845]
18 BADTIME Signature out of time window [RFC2845]
19 BADMODE Bad TKEY Mode [RFC2930]
20 BADNAME Duplicate key name [RFC2930]
21 BADALG Algorithm not supported [RFC2930]
22 BADTRUNC Bad Truncation [RFC4635]
23 - 3,840
0x0017 - 0x0F00 Unassigned
3,841 - 4,095
0x0F01 - 0x0FFF Reserved for Private Use
4,096 - 65,534
0x1000 - 0xFFFE Unassigned
0xFFFF Reserved; can only be allocated by Standards
Note on error number 9 (NotAuth): This error number means either
"Not Authoritative" [RFC2136] or "Not Authorized" [RFC2845]. If 9
appears as the RCODE in the header of a DNS response without a
TSIG RR or with a TSIG RR having a zero error field, then it means
"Not Authoritative". If 9 appears as the RCODE in the header of a
DNS response that includes a TSIG RR with a non-zero error field,
then it means "Not Authorized".
Since it is important that RCODEs be understood for interoperability,
assignment of a new RCODE in the ranges listed above as "Unassigned"
requires an IETF Review.
3. DNS Resource Records
All RRs have the same top-level format, shown in the figure below
taken from [RFC1035].
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
/ NAME /
| TYPE |
| CLASS |
| TTL |
| RDLENGTH |
/ RDATA /
NAME is an owner name, i.e., the name of the node to which this
resource record pertains. NAMEs are specific to a CLASS as described
in Section 3.2. NAMEs consist of an ordered sequence of one or more
labels, each of which has a label type [RFC1035] [RFC6891].
TYPE is a 2-octet unsigned integer containing one of the RRTYPE
codes. See Section 3.1.
CLASS is a 2-octet unsigned integer containing one of the RR CLASS
codes. See Section 3.2.
TTL is a 4-octet (32-bit) unsigned integer that specifies, for data
TYPEs, the number of seconds that the resource record may be cached
before the source of the information should again be consulted. Zero
is interpreted to mean that the RR can only be used for the
transaction in progress.
RDLENGTH is an unsigned 16-bit integer that specifies the length in
octets of the RDATA field.
RDATA is a variable-length string of octets that constitutes the
resource. The format of this information varies according to the
TYPE and, in some cases, the CLASS of the resource record.
3.1. RRTYPE IANA Considerations
There are three subcategories of RRTYPE numbers: data TYPEs, QTYPEs,
Data TYPEs are the means of storing data. QTYPES can only be used in
queries. Meta-TYPEs designate transient data associated with a
particular DNS message and, in some cases, can also be used in
queries. Thus far, data TYPEs have been assigned from 1 upward, plus
the block from 100 through 103, and from 32,768 upward, while Q and
Meta-TYPEs have been assigned from 255 downward except for the OPT
Meta-RR, which is assigned TYPE 41. There have been DNS
implementations that made caching decisions based on the top bit of
the bottom byte of the RRTYPE.
There are currently three Meta-TYPEs assigned: OPT [RFC6891], TSIG
[RFC2845], and TKEY [RFC2930]. There are currently five QTYPEs
assigned: * (ALL/ANY), MAILA, MAILB, AXFR, and IXFR.
Allocated RRTYPEs have mnemonics that must be completely disjoint
from the mnemonics used for CLASSes and that must match the regular
expression below. In addition, the generic CLASS and RRTYPE names
specified in Section 5 of [RFC3597] cannot be assigned as new RRTYPE
Considerations for the allocation of new RRTYPEs are as follows:
Hexadecimal Assignment Policy
0x0000 RRTYPE zero is used as a special indicator for the
SIG(0) RR [RFC2931] [RFC4034] and in other
circumstances and must never be allocated for
1 - 127
0x0001 - 0x007F Remaining RRTYPEs in this range are assigned for
data TYPEs by the DNS RRTYPE Allocation Policy as
specified in Section 3.1.1.
128 - 255
0x0080 - 0x00FF Remaining RRTYPEs in this range are assigned for Q
and Meta-TYPEs by the DNS RRTYPE Allocation Policy
as specified in Section 3.1.1.
256 - 61,439
0x0100 - 0xEFFF Remaining RRTYPEs in this range are assigned for
data RRTYPEs by the DNS RRTYPE Allocation Policy
as specified in Section 3.1.1. (32,768 and 32,769
(0x8000 and 0x8001) have been assigned.)
61,440 - 65,279
0xF000 - 0xFEFF Reserved for future use. IETF Review required to
65,280 - 65,534
0xFF00 - 0xFFFE Reserved for Private Use.
0xFFFF Reserved (Standards Action)
3.1.1. DNS RRTYPE Allocation Policy
Parameter values specified in Section 3.1 above, as assigned based on
DNS RRTYPE Allocation Policy, are allocated by Expert Review if they
meet the two requirements listed below. There will be a pool of a
small number of Experts appointed by the IESG. Each application will
be judged by an Expert selected by IANA. In any case where the
selected Expert is unavailable or states they have a conflict of
interest, IANA may select another Expert from the pool. Some
guidelines for the Experts are given in Section 3.1.2.
RRTYPEs that do not meet the requirements below may nonetheless be
allocated by a Standards Action with early allocation permitted as
specified in [RFC4020].
1. A complete template as specified in Appendix A has been posted to
the email@example.com mailing list and received by
Note that the posting of partially completed, draft, or formally
submitted templates to firstname.lastname@example.org by the applicant or Expert
for comment and discussion is highly encouraged. Before formal
submission of an RRTYPE template, we recommend submitting it for
community review and considering the responses in order to reduce
the probability of initial rejection and the need for modification
2. The RR for which an RRTYPE code is being requested is either (a) a
data TYPE that can be handled as an Unknown RR as described in
[RFC3597] or (b) a Meta-TYPE whose processing is optional, i.e.,
it is safe to simply discard RRs with that Meta-TYPE in queries or
Note that such RRs may include additional section processing,
provided such processing is optional.
After the applicant submits their formal application to IANA by
sending the completed template specified in Appendix A to the
email@example.com mailing list, IANA appoints an
Expert and sends the completed template to the Expert, copying the
applicant. No more than two weeks after receiving the application,
the Expert shall explicitly approve or reject the application,
informing IANA, the applicant, and the firstname.lastname@example.org mailing list.
A rejection should include the reason for rejection and may include
suggestions for improvement. The Expert should consult with other
technical experts and the email@example.com mailing list as necessary.
If the Expert does not approve the application within this period, it
is considered rejected. IANA should report non-responsive Experts to
IANA shall maintain a public archive of approved templates. In
addition, if the required description of the RRTYPE applied for is
referenced by URL, a copy of the document so referenced should be
included in the archive.
3.1.2. DNS RRTYPE Expert Guidelines
The Designated Expert should normally be lenient, preferring to
approve most requests. However, the Expert should usually reject any
RRTYPE allocation request that meets one or more of the following
1. The request was documented in a manner that was not sufficiently
clear or complete to evaluate or implement. (Additional
documentation can be provided during the Expert Review period.)
2. The proposed RRTYPE or RRTYPEs affect DNS processing and do not
meet the criteria in point 2 of Section 3.1.1 above.
3. Application use as documented makes incorrect assumptions about
DNS protocol behavior, such as wildcards, CNAME, DNAME, etc.
4. An excessive number of RRTYPE values is being requested when the
purpose could be met with a smaller number of values or with
Private Use values.
3.1.3. Special Note on the OPT RR
The OPT (OPTion) RR (RRTYPE 41) and its IANA considerations are
specified in [RFC6891]. Its primary purpose is to extend the
effective field size of various DNS fields, including RCODE, label
type, OpCode, flag bits, and RDATA size. In particular, for
resolvers and servers that recognize it, it extends the RCODE field
from 4 to 12 bits.
3.1.4. The AFSDB RR Subtype Field
The AFSDB RR [RFC1183] is a CLASS-insensitive RR that has the same
RDATA field structure as the MX RR [RFC1035], but the 16-bit unsigned
integer field at the beginning of the RDATA is interpreted as a
subtype as shown below. Use of the AFSDB RR to locate AFS cell
database servers was deprecated by [RFC5864]. This subtype registry
is hereby closed, and allocation of new subtypes is no longer
Hexadecimal Assignment Policy
0x0000 Reserved; registry closed
0x0001 AFS v3.0 Location Service [RFC1183]
0x0002 DCE/NCA root cell directory node [RFC1183]
3 - 65,279
0x0003 - 0xFEFF Not allocated; registry closed
65,280 - 65,534
0xFF00 - 0xFFFE Private Use
0xFFFF Reserved; registry closed
3.2. RR CLASS IANA Considerations
There are currently two subcategories of DNS CLASSes: normal, data-
containing classes; and QCLASSes that are only meaningful in queries
DNS CLASSes have been little used but constitute another dimension of
the DNS distributed database. In particular, there is no necessary
relationship between the namespace or root servers for one data CLASS
and those for another data CLASS. The same DNS NAME can have
completely different meanings in different CLASSes. The label types
are the same, and the null label is usable only as root in every
CLASS. As global networking and DNS have evolved, the IN, or
Internet, CLASS has dominated DNS use.
As yet, there has not been a requirement for "Meta-CLASSes". That
would be a CLASS to designate transient data associated with a
particular DNS message, which might be usable in queries. However,
it is possible that there might be a future requirement for one or
Assigned CLASSes have mnemonics that must be completely disjoint from
the mnemonics used for RRTYPEs and that must match the regular
expression below. In addition, the generic CLASS and RRTYPE names
specified in Section 5 of [RFC3597] cannot be assigned as new CLASS
The current CLASS assignments and considerations for future
assignments are as follows:
Hexadecimal Assignment / Policy, Reference
0x0000 Reserved; assignment requires a Standards Action.
0x0001 Internet (IN) [RFC1035]
0x0002 Available for assignment by IETF Review as a data
0x0003 Chaos (CH) [Moon1981]
0x0004 Hesiod (HS) [Dyer1987]
5 - 127
0x0005 - 0x007F Available for assignment by IETF Review for data
128 - 253
0x0080 - 0x00FD Available for assignment by IETF Review for
QCLASSes and Meta-CLASSes only.
0x00FE QCLASS NONE [RFC2136]
0x00FF QCLASS * (ANY) [RFC1035]
256 - 32,767
0x0100 - 0x7FFF Available for assignment by IETF Review.
32,768 - 57,343
0x8000 - 0xDFFF Available for assignment to data CLASSes only;
57,344 - 65,279
0xE000 - 0xFEFF Available for assignment to QCLASSes and
Meta-CLASSes only; Specification Required.
65,280 - 65,534
0xFF00 - 0xFFFE Private Use
0xFFFF Reserved; can only be assigned by a Standards
3.3. Label Considerations
DNS NAMEs are sequences of labels [RFC1035].
3.3.1. Label Types
At the present time, there are two categories of label types: data
labels and compression labels. Compression labels are pointers to
data labels elsewhere within an RR or DNS message and are intended to
shorten the wire encoding of NAMEs.
The two existing data label types are sometimes referred to as Text
and Binary. Text labels can, in fact, include any octet value
including zero-value octets, but many current uses involve only
printing ASCII characters [US-ASCII]. For retrieval, Text labels are
defined to treat ASCII uppercase and lowercase letter codes as
matching [RFC4343]. Binary labels are bit sequences [RFC2673]. The
Binary Label type is Historic [RFC6891].
3.3.2. Label Contents and Use
The last label in each NAME is "ROOT", which is the zero-length
label. By definition, the null or ROOT label cannot be used for any
other NAME purpose.
NAMEs are local to a CLASS. The Hesiod [Dyer1987] and Chaos
[Moon1981] CLASSes are for essentially local use. The IN, or
Internet, CLASS is thus the only DNS CLASS in global use on the
Internet at this time.
A somewhat out-of-date description of name allocation in the IN CLASS
is given in [RFC1591]. Some information on reserved top-level domain
names is in BCP 32 [RFC2606].
4. Security Considerations
This document addresses IANA considerations in the allocation of
general DNS parameters, not security. See [RFC4033], [RFC4034], and
[RFC4035] for secure DNS considerations.
5. IANA Considerations
This document consists entirely of DNS IANA considerations.
IANA has established a process for accepting Appendix A templates and
selecting an Expert from those appointed to review such template form
applications. IANA forwards the template to the Expert, copying the
applicant. IANA archives and makes available all approved RRTYPE
allocation templates and referred documentation (unless it is readily
available at a stable URI). It is the duty of the applicant to post
the formal application template to the
firstname.lastname@example.org mailing list, which IANA will
monitor. The email@example.com mailing list is for community
discussion and comment. See Section 3.1 and Appendix A for more
Appendix A. RRTYPE Allocation Template
DNS RRTYPE PARAMETER ALLOCATION TEMPLATE
When ready for formal consideration, this template is to be submitted
to IANA for processing by emailing the template to dns-rrtype-
A. Submission Date:
B.1 Submission Type: [ ] New RRTYPE [ ] Modification to RRTYPE
B.2 Kind of RR: [ ] Data RR [ ] Meta-RR
C. Contact Information for submitter (will be publicly posted):
Name: Email Address:
International telephone number:
Other contact handles:
D. Motivation for the new RRTYPE application.
Please keep this part at a high level to inform the Expert and
reviewers about uses of the RRTYPE. Most reviewers will be DNS
experts that may have limited knowledge of your application space.
E. Description of the proposed RR type.
This description can be provided in-line in the template, as an
attachment, or with a publicly available URL.
F. What existing RRTYPE or RRTYPEs come closest to filling that need
and why are they unsatisfactory?
G. What mnemonic is requested for the new RRTYPE (optional)?
Note: If a mnemonic is not supplied, not allowed, or duplicates an
existing RRTYPE or CLASS mnemonic, the Expert will assign a
H. Does the requested RRTYPE make use of any existing IANA registry
or require the creation of a new IANA subregistry in DNS
Parameters? If so, please indicate which registry is to be used
or created. If a new subregistry is needed, specify the
allocation policy for it and its initial contents. Also include
what the modification procedures will be.
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 [RFC3597])?
Appendix B. Changes from RFC 6195
Dropped description of changes from RFC 5395 to [RFC6195], since
those changes have already happened and we don't need to do them
again. Added description of changes from [RFC6195] to this document.
Cut back RRTYPE Expert Review period to two weeks and eliminated the
mandatory firstname.lastname@example.org comment period. Changed workflow
description for RRTYPE review and allocation to correspond more
closely to actual practice.
Closed the AFSDB subtype registry and added an informative reference
to [RFC5864] where the use of the AFSDB RR to locate AFS cell
database servers is deprecated.
Clarified IANA archiving of referenced documentation as well as
approved RRTYPE application template.
In the RRTYPE application template, changed the label of question "B"
to "B.1" and added "B.2" to ask about the kind of RR.
Added text and an exclusory regular expression to Sections 3.1 and
3.2 to prohibit the use of a slight generalization of the generic
CLASS and RRTYPE names specified in [RFC3597] as the mnemonics for
new CLASSes and RRTYPEs.
Parenthetically listed "ANY" as well as "ALL" as a meaning for the
Clarified that there is one DNS error number space for headers, OPT
extended headers, TSIG RRs, and TKEY RRs. Noted that this is
considered to update [RFC2845] and [RFC2930]. Noted the overloading
of error number 9 as well as 16.
Updated references for revised versions.
Incorporated a number of editorial changes and typo fixes.
[RFC1034] Mockapetris, P., "Domain names - concepts and
facilities", STD 13, RFC 1034, November 1987.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone
Changes (DNS NOTIFY)", RFC 1996, August 1996.
[RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)",
RFC 2136, April 1997.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, July 1997.
[RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
Wellington, "Secret Key Transaction Authentication for
DNS (TSIG)", RFC 2845, May 2000.
[RFC2930] Eastlake 3rd, D., "Secret Key Establishment for DNS (TKEY
RR)", RFC 2930, September 2000.
[RFC3425] Lawrence, D., "Obsoleting IQUERY", RFC 3425,
[RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record
(RR) Types", RFC 3597, September 2003.
[RFC4020] Kompella, K. and A. Zinin, "Early IANA Allocation of
Standards Track Code Points", BCP 100, RFC 4020,
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, March 2005.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, March 2005.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005.
[RFC4635] Eastlake 3rd, D., "HMAC SHA (Hashed Message
Authentication Code, Secure Hash Algorithm) TSIG
Algorithm Identifiers", RFC 4635, August 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
[RFC6840] Weiler, S., Ed., and D. Blacka, Ed., "Clarifications and
Implementation Notes for DNS Security (DNSSEC)",
RFC 6840, February 2013.
[RFC6891] Damas, J., Graff, M., and Vixie, P., "Extension
Mechanisms for DNS (EDNS(0))", STD 75, RFC 6891, April
[US-ASCII] American National Standards Institute (formerly United
States of America Standards Institute), "USA Code for
Information Interchange", ANSI X3.4-1968, 1968.
ANSI X3.4-1968 has been replaced by newer versions with
slight modifications, but the 1968 version remains
definitive for the Internet.
[Dyer1987] Dyer, S., and F. Hsu, "Hesiod", Project Athena Technical
Plan - Name Service, April 1987.
[Moon1981] Moon, D., "Chaosnet", A.I. Memo 628, Massachusetts
Institute of Technology Artificial Intelligence
Laboratory, June 1981.
[RFC1183] Everhart, C., Mamakos, L., Ullmann, R., and P.
Mockapetris, "New DNS RR Definitions", RFC 1183,
[RFC1591] Postel, J., "Domain Name System Structure and
Delegation", RFC 1591, March 1994.
[RFC2606] Eastlake 3rd, D. and A. Panitz, "Reserved Top Level DNS
Names", BCP 32, RFC 2606, June 1999.
[RFC2673] Crawford, M., "Binary Labels in the Domain Name System",
RFC 2673, August 1999.
[RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures
( SIG(0)s )", RFC 2931, September 2000.
[RFC4343] Eastlake 3rd, D., "Domain Name System (DNS) Case
Insensitivity Clarification", RFC 4343, January 2006.
[RFC5864] Allbery, R., "DNS SRV Resource Records for AFS",
RFC 5864, April 2010.
[RFC6195] Eastlake 3rd, D., "Domain Name System (DNS) IANA
Considerations", RFC 6195, March 2011.
Alfred Hoenes' contributions are gratefully acknowledged as are those
by Mark Andrews, Dick Franks, and Michael Sheldon.
Donald E. Eastlake 3rd
155 Beaver Street
Milford, MA 01757