DNS Multiple QTYPEs
draft-ietf-dnssd-multi-qtypes-14
| Document | Type | Active Internet-Draft (dnssd WG) | |
|---|---|---|---|
| Author | Ray Bellis | ||
| Last updated | 2026-03-06 (Latest revision 2026-02-27) | ||
| Replaces | draft-bellis-dnsext-multi-qtypes | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
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| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Tim Wicinski | ||
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draft-ietf-dnssd-multi-qtypes-14
DNSSD R. Bellis
Internet-Draft ISC
Intended status: Standards Track 27 February 2026
Expires: 31 August 2026
DNS Multiple QTYPEs
draft-ietf-dnssd-multi-qtypes-14
Abstract
This document specifies a method for a DNS client to request
additional DNS record types to be delivered alongside the primary
record type specified in the question section of a DNS QUERY
(OpCode=0).
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://dnssd-
wg.github.io/draft-ietf-dnssd-multi-qtypes/draft-ietf-dnssd-multi-
qtypes.html. Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-dnssd-multi-qtypes/.
Discussion of this document takes place on the DNSSD Working Group
mailing list (mailto:dnssd@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/dnssd/. Subscribe at
https://www.ietf.org/mailman/listinfo/dnssd/.
Source for this draft and an issue tracker can be found at
https://github.com/dnssd-wg/draft-ietf-dnssd-multi-qtypes.
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-
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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."
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This Internet-Draft will expire on 31 August 2026.
Copyright Notice
Copyright (c) 2026 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Specification . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Multiple QTYPE EDNS Options Format . . . . . . . . . . . 3
3.2. Client Request Generation . . . . . . . . . . . . . . . . 4
3.3. Server Request Parsing . . . . . . . . . . . . . . . . . 5
3.4. Server Response Generation . . . . . . . . . . . . . . . 5
3.5. Client Response Processing . . . . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
References . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Normative References . . . . . . . . . . . . . . . . . . . . . 9
Informative References . . . . . . . . . . . . . . . . . . . . 9
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . 10
A.1. Stub query for A with MQType-Query for AAAA + HTTPS . . . 10
A.2. Stub query for DS with MQType-Query for DNSKEY . . . . . 11
A.3. Recursive query for DS with MQType-Query for NS . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
A commonly requested DNS [STD13] feature is the ability to receive
multiple related resource records (RRs) in a single DNS response.
For example, it may be desirable to receive the A, AAAA, and HTTPS
RRs for a domain name together, rather than having to issue multiple
queries.
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The DNS wire protocol in theory supported having multiple questions
in a single packet, but in practice this does not work. In
[RFC9619], RFC1035 is updated to only permit a single question in a
QUERY (OpCode=0) request.
Sending QTYPE=ANY does not guarantee that all resource record sets
(RRsets) will be returned. Section 4.1 of [RFC8482] specifies that
responders may return a single RRset of their choosing.
This document provides a solution for those cases where only the
QTYPE varies by specifying a new option for the Extension Mechanisms
for DNS (EDNS) [RFC6891] that contains an additional list of QTYPE
values that the client wishes to receive in addition to the single
QTYPE appearing in the question section. A different EDNS option is
used in response packets as protection against DNS middleboxes that
echo EDNS options verbatim.
The specification described herein is applicable both for queries
from a stub resolver to recursive servers, and from recursive
resolvers to authoritative servers. It does not apply to Multicast
DNS queries [RFC6762], which are already designed to allow requesting
multiple records in a single query, but is applicable to DNS-Based
Service Discovery (DNS-SD) [RFC6763].
2. Terminology
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.
This document makes use of DNS terminology defined in [RFC9499].
3. Specification
3.1. Multiple QTYPE EDNS Options Format
The overall format of an EDNS option is shown for reference in
Figure 1, per [RFC6891], followed by the option specific data.
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+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | |
: OPTION-DATA :
| |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 1: EDNS Option Format
OPTION-CODE: MQTYPE-Query (20) in queries and MQTYPE-Response (21) in
responses.
OPTION-LENGTH: Size (in octets) of OPTION-DATA.
OPTION-DATA: Option specific, as depicted in Figure 2.
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | QT1 |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | |
: ... :
| |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| QTn |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 2: MQTYPE OPTION-DATA Format
A list of 2-octet values in network order (MSB first) each specifying
a DNS RRTYPE that must be for a data RRTYPE as described in
Section 3.1 of [RFC6895]. Individual values from the list (with
unspecified index "x") are referred to as QTx in the following
sections.
3.2. Client Request Generation
DNS clients implementing this specification MUST generate packets
that conform to the server request parsing rules described in
Section 3.3.
The choice of when a client implementation should attempt to coalesce
queries for multiple QTYPEs using this method is implementation
specific and not discussed further herein. However, careful
considerations should be taken into account when coalescing queries
on behalf of an application if such a feature is not explicitly
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requested by the application. How an application interacts with an
underlying name resolution library is internal to the implementation
and is thus out of scope.
3.3. Server Request Parsing
In addition to the error cases discussion in Section 7 of [RFC6891],
the server MUST return a FORMERR response if the server receives:
* An MQTYPE-Query option in any inbound DNS message with an OpCode
other than QUERY (0).
* An MQTYPE-Response option in any inbound DNS message.
* More than one MQTYPE-Query option in a query.
* An MQTYPE-Query in a query that contains no primary question (i.e.
QDCOUNT=0).
* An MQTYPE-Query option in a query where the primary question is a
non-data RRTYPE (e.g. ANY, AXFR).
* An MQTYPE-Query option with an empty QT list.
* An invalid QTx (e.g. one corresponding to a Meta RRTYPE).
* A duplicate QTx (or one duplicating the primary QTYPE field) in a
query.
3.4. Server Response Generation
A conforming server that receives an MQTYPE-Query option in a valid
query MUST return an MQTYPE-Response option in its response, even if
that response is truncated (TC=1). This is necessary to indicate
that the server does support this extension. Refer to Section 3.3
for invalid queries.
The server MUST first start constructing a response for the primary
(QNAME, QCLASS, QTYPE) tuple specified in the Question section per
the existing DNS sections. The RCODE and all other flags (such as AA
or AD) MUST be determined at this time.
If this initial response results in truncation (TC=1) then the
additional queries specified in the MQTYPE-Query option MUST NOT be
processed.
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After the initial response is prepared, the server MUST attempt to
combine the responses for individual (QNAME, QCLASS, QTx)
combinations into the response for the first query. If a recursive
server does not yet have those responses available it MAY first make
appropriate outbound queries to populate its caches.
For each individual combination the server MUST evaluate the
resulting RCODE and other flags and check that they all match the
values generated from the primary query.
If any mismatch is detected the mismatching additional response MUST
NOT be included in the final combined response and its QTx value MUST
NOT be included in the MQTYPE-Response option's list. This might
happen, for example, if the primary query resulted in a NOERROR
response but a QTx query resulted in a SERVFAIL, or if the primary
response has AA=0 but a QTx response has AA=1, such as might happen
if the NS and DS records were both requested at the parent side of a
zone cut.
The server MUST attempt to combine the remaining individual RRs into
the same sections in which they would have appeared in a standalone
query, i.e. as if each combination had been "the question" per
Section 4.1 of [RFC1035].
The server MUST detect duplicate RRs and keep only a single copy of
each RR in its respective section. Duplicates can occur, for
example, in the Answer section if a CNAME chain is involved, or in
the Authority section if multiple QTYPEs don't exist, etc. Note that
RRs can be legitimately duplicated in different sections such as for
the (SOA, TYPE12345) combination at a zone apex where TYPE12345 is
not present.
Handling of an MQTYPE-Query option MUST NOT itself trigger a
truncated response. If response size (or other) limits do not allow
all of the data obtained by querying for an additional QTx to be
included in the final response in their entirety (i.e. as complete
RRsets) then the server MUST NOT include the respective QTx in the
MQTYPE-Response option's list and MAY stop processing further QTx
combinations.
If all RRs for a single QTx combination fit into the message then the
server MUST include the respective QTx in the MQTYPE-Response
option's list to indicate that the given query type was completely
processed.
Note that it is possible for the resulting MQTYPE-Response option to
contain an empty list, but as described above the option must still
be returned.
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3.5. Client Response Processing
If the response to a query containing an MQTYPE-Query option does not
contain an MQTYPE-Response option, or if it erroneously contains an
MQTYPE-Query option, the client MUST treat the response as if this
option is unsupported by the server and MUST process the primary
response as if the MQTYPE-Query option had not been used.
In the above case, or if the server generates a FORMERR response, the
client MUST issue additional standalone queries (that is, without
using the MQTYPE-Query option) for all QTYPEs for which an answer is
still required.
If the MQTYPE-Response option is present more than once or if a QTx
value is duplicated (or duplicates the primary QTYPE field) the
client MUST treat the answer as invalid (equivalent to FORMERR).
The Question section and the list of types present in the MQTYPE-
Response option indicates the list of (QNAME, QCLASS, qtypes)
combinations which are completely answered and contained within the
received response. The answers to all query combinations share the
same RCODE and all other flags.
All RRs required by existing DNS specifications are expected to be
present in the respective sections of the DNS message, including
proofs of nonexistence where required. The client MUST NOT rely on
any particular order of RRs in the message sections.
For the purposes of Section 5.4.1 of [RFC2181] any authoritative
answers received MUST be ranked the same as the answer for the
primary question.
Clients MUST take into account that individual RRs might originate
from different DNS zones and that proofs of non-existence might have
been produced by different signers.
Absence of QTx values which were requested by the client but are not
present in the MQTYPE-Response option indicates that:
* (for responses from recursive servers) the server does not have
any records for that QTx value in cache, and/or
* the individual responses could not be combined into one message
because of RCODE or other flag mismatches, and/or
* the server was unwilling to process the request (for example,
because a limit was exceeded), and/or
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* the response size limit would be exceeded
The client MUST subsequently initiate separate standalone queries for
all QTx values for which an answer is still required.
4. Security Considerations
The method documented here does not change any of the security
properties of the DNS protocol itself.
It should however be noted that this method does increase the
potential amplification factor when the DNS protocol is used as a
vector for a denial-of-service attack. A further risk is being able
to maliciously cause recursive servers to perform large amounts of
additional work.
Implementors SHOULD therefore allow operators to configure limits on
the number of QTx values specified and/or the resulting response
size. The recommended values of those limits will depend on the
environment in which this specification is used. In public DNS it is
expected that a limit of four QTx values would be appropriate, but
when used with DNS-SD or within private networks higher limits would
be acceptable.
5. IANA Considerations
IANA has assigned the following values in the "DNS EDNS0 Option Codes
(OPT)" registry within "Domain Name System (DNS) Parameters" registry
group:
+=======+=================+==========+===========+
| Value | Name | Status | Reference |
+=======+=================+==========+===========+
| 20 | MQTYPE-Query | Optional | RFC TBD |
+-------+-----------------+----------+-----------+
| 21 | MQTYPE-Response | Optional | RFC TBD |
+-------+-----------------+----------+-----------+
Table 1: MQTYPE EDNS Option Numbers
Acknowledgements
The author wishes to thank the following for their feedback and
reviews during the initial development of this document: Michael
Graff, Olafur Gudmundsson, Matthijs Mekking, and Paul Vixie.
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In addition the author wishes to thank the following for subsequent
review during discussion in the DNSSD Working Group: Chris Box,
Stuart Cheshire, Esko Dijk, Ted Lemon, David Schinazi and Petr
Spacek.
References
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/rfc/rfc2119>.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
<https://www.rfc-editor.org/rfc/rfc2181>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013,
<https://www.rfc-editor.org/rfc/rfc6891>.
[RFC6895] Eastlake 3rd, D., "Domain Name System (DNS) IANA
Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895,
April 2013, <https://www.rfc-editor.org/rfc/rfc6895>.
[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/rfc/rfc8174>.
[RFC9619] Bellis, R. and J. Abley, "In the DNS, QDCOUNT Is (Usually)
One", RFC 9619, DOI 10.17487/RFC9619, July 2024,
<https://www.rfc-editor.org/rfc/rfc9619>.
[STD13] Internet Standard 13,
<https://www.rfc-editor.org/info/std13>.
At the time of writing, this STD comprises the following:
Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
Informative References
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[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<https://www.rfc-editor.org/rfc/rfc6762>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/rfc/rfc6763>.
[RFC8482] Abley, J., Gudmundsson, O., Majkowski, M., and E. Hunt,
"Providing Minimal-Sized Responses to DNS Queries That
Have QTYPE=ANY", RFC 8482, DOI 10.17487/RFC8482, January
2019, <https://www.rfc-editor.org/rfc/rfc8482>.
[RFC9499] Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219,
RFC 9499, DOI 10.17487/RFC9499, March 2024,
<https://www.rfc-editor.org/rfc/rfc9499>.
Appendix A. Examples
The examples below are shown as might be reported by the ISC Dig
utility. For the purposes of brevity irrelevant content is omitted.
A.1. Stub query for A with MQType-Query for AAAA + HTTPS
In this example a stub resolver has requested the A record for
www.example.com, along with an MQTYPE-Query option requesting AAAA
and HTTPS records. The stub resolver has also set the DO bit,
indicating DNSSEC support.
The presence of the HTTPS QTYPE in the MQTYPE-Response option of the
response coupled with its absence from the answer section indicates
that the recursive server currently holds no data for this QTYPE.
The corresponding type fields in the NSEC3 record further provide a
cryptographic proof of non-existence for the HTTPS QTYPE and the SOA
record also indicates a "negative answer".
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;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 11111
;; flags: qr rd ra ad
;; QUERY: 1, ANSWER: 4, AUTHORITY: 4, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags: do; udp: 1232
; MQTYPE-Response: AAAA HTTPS
;; QUESTION SECTION:
;www.example.com. IN A
;; ANSWER SECTION:
www.example.com. 2849 IN A 192.0.2.1
www.example.com. 2849 IN RRSIG A [...]
www.example.com. 3552 IN AAAA 3fff::1234
www.example.com. 3552 IN RRSIG AAAA [...]
;; AUTHORITY SECTION:
example.com. 2830 IN SOA ns.example.com. [...]
example.com. 2830 IN RRSIG SOA 13 2 [...]
[...].example.com. 2830 IN NSEC3 [...] A TXT AAAA RRSIG
[...].example.com. 2830 IN RRSIG NSEC3 [...]
Figure 3: A + AAAA + HTTPS
A.2. Stub query for DS with MQType-Query for DNSKEY
In this similar example, the primary QTYPE is for DS and the MQTYPE-
Query field only contains DNSKEY.
Both the DS and DNSKEY records are returned, along with their
corresponding RRSIG records.
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;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 33333
;; flags: qr rd ra ad
;; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags: do; udp: 1232
; MQTYPE-Response: DNSKEY
;; QUESTION SECTION:
;example.com. IN DS
;; ANSWER SECTION:
example.com. 625 IN DNSKEY 256 3 13 [...]
example.com. 625 IN DNSKEY 257 3 13 [...]
example.com. 625 IN RRSIG DNSKEY [...] example.com. [...]
example.com. 86185 IN DS 370 13 2 [...]
example.com. 86185 IN RRSIG DS [...] com. [...]
Figure 4: Stub DS + DNSKEY
A.3. Recursive query for DS with MQType-Query for NS
In this instance, a recursive resolver is sending a DS record query
to the parent zone's authoritative server and simultaneously
requesting the NS records for the zone.
Since the DS record response is marked as authoritative (AA = 1) but
the NS record data on the parent side of a zone cut is not
authoritative (AA = 0) the server is unable to merge the responses,
and the NS QTYPE is omitted from the MQTYPE-Response field.
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 33333
;; flags: qr aa
;; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags: do; udp: 1232
; MQTYPE-Response: [empty]
;; QUESTION SECTION:
;example.com. IN DS
;; ANSWER SECTION:
example.com. 86185 IN DS 370 13 2 [...]
example.com. 86185 IN RRSIG DS [...] com. [...]
Figure 5: Recursive DS + NS
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Author's Address
Ray Bellis
Internet Systems Consortium, Inc.
PO Box 360
Newmarket, NH 03857
United States of America
Phone: +1 650 423 1300
Email: ray@isc.org
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