dnsop J. Yao
Internet-Draft P. Vixie
Intended status: Standards Track CNNIC-Farsight Joint Laboratory
Expires: May 3, 2017 N. Kong
X. Li
CNNIC
October 30, 2016
A DNS Query including A Main Question with Accompanying Questions
draft-yao-dnsop-accompanying-questions-02
Abstract
This document enables DNS initiators to send a main question
accompanying with several related questions in a single DNS query,
and enables DNS responders to put the answers into a single DNS
response. This mechanism can reduce the number of DNS round-trips
per application work-unit.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Mechanism for a main question with accompanying questions . . 3
4. Responder Processing . . . . . . . . . . . . . . . . . . . . 5
5. Initiator Processing . . . . . . . . . . . . . . . . . . . . 6
6. Query and Response Example . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. Change History . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. draft-yao-dnsop-accompanying-questions: Version 00 . . . 9
10.2. draft-yao-dnsop-accompanying-questions: Version 01 . . . 9
10.3. draft-yao-dnsop-accompanying-questions: Version 02 . . . 9
11. Normative References . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
There are many scenarios in which an application must send several
related questions to a DNS responder. For examples, when asking
about a QTYPE=A RRset, a QTYPE=AAAA RRset may also be of use [RFC
5321]; When asking for some RRset of www.example.com about A and
AAAA, records of a sub-domain name such as _443._tcp.www.example.com
for TLSA may be of interest[RFC 6698].
Query example.com for A and AAAA
Query www.example.com for A and AAAA, and _443._tcp.www.example.com
for TLSA
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This document describes a method by which DNS initiators can send a
main question accompanying with several related questions in a single
DNS query, and enables DNS responders place all related answers into
a single DNS response. This mechanism can reduce the number of DNS
round-trips per application work-unit, by carrying several related
queries in a single query transaction.
2. Terminology
The basic key words such as "MUST", "MUST NOT", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "MAY", and "MAYNOT" are to be interpreted as
described in [RFC2119].
The basic DNS terms used in this specification are defined in the
documents [RFC1034] and [RFC1035].
3. Mechanism for a main question with accompanying questions
The initiator still puts a main question into the question section of
the DNS query packet, as described in [RFC1035]. Accompanying
questions will be put into the variable part of an OPT RR [RFC6891].
The variable part of an OPT RR is encoded in its RDATA and is
structured as the following:
+0 (MSB) +1 (LSB)
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | |
/ OPTION-DATA /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
OPTION-CODE (Assigned by IANA.)
OPTION-LENGTH Size (in octets) of OPTION-DATA.
OPTION-DATA including at most 8 accompanying questions with AQ-RCODE.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| Reserved | AQ-RCODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
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| AQ-TYPE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-ANCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-NSCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-ARCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| |
/ Prefix /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| Reserved | AQ-RCODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-TYPE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-ANCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-NSCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-ARCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| |
/ Prefix /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| Reserved | AQ-RCODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-TYPE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-ANCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-NSCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-ARCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| |
/ Prefix /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| |
/ ...... /
/ /
o Reserved field is kept for the future use.
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o AQ-RCODE field will be set to 111111110100 bits when being
initialized. The AQ-RCODE with the value of 111111110100 bits
means that the mechanism for accompanying has not been
implemented, where "0100" in the RCODE value means "not been
implemented". The AQ aware responders will put the RCODE value
for the query of this question into AQ-RCODE fields.
o AQ-ANCOUNT field will indicate the number of resource records in
the answer section for this accompanying question. The AQ aware
responders will put the ANCOUNT value for the query of this
question into AQ-ANCOUNT field.
o AQ-NSCOUNT field will indicate the number of name server resource
records in the authority records section for this accompanying
question. The AQ aware responders will put the NSCOUNT value for
the query of this question into AQ-NSCOUNT field.
o AQ-ARCOUNT field will indicate the number of resource records in
the additional records section for this accompanying question.
The AQ aware responders will put the ARCOUNT value for the query
of this question into AQ-ARCOUNT field.
o Prefix field indicates a domain name with the form of a pointer or
a sequence of labels ending with a pointer using the message
compression defined in section 4.1.4. of RFC 1035. The domain
name for accompanying questions MUST be same with the domain name
for a main question or be children name of it. For an example, if
the main domain name is example.com and the accompanying domain
name is mail.example.com., the prefix is "mail." ending with a
pointer pointing to "example.com.".
4. Responder Processing
The AQ aware responder will check the main question first, and put
the results into the DNS response packet following RFC 1034. If the
AQ OPT is present, the responder assembles the prefix with the main
domain name and makes it to be an accompanying question, checks the
accompanying questions in order, and put the results into the DNS
answer section, authority section or additional records section of
the response following RFC 1034; but the response code is placed in
the respective AQ-RCODE field in AQ OPT of the response. The RCODE
field in the DNS response header refers to the main question only.
The AQ aware responders will put the ANCOUNT, NSCOUNT and ARCOUNT
value for the query of this accompanying question into the respective
AQ-ANCOUNT, AQ-NSCOUNT and AQ-ARCOUNT fields. The ANCOUNT, NSCOUNT
and ARCOUNT fields in the DNS response header refer to the main
question only. When the answer is negative for the accompanying
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question, the SOA resource record will be put in the authority
section.
The mechanism proposed in this document is intended for both between
stub resolvers and recursive resolvers, and between recursive
resolvers and authoritative servers. Most DNS resource records
needed to process parallel query are normally located in the same
zone. In case of that some children domain names are delegated and
not in the main domain name's zone, the delegation information will
be returned to the recursive resolvers. The recursive resolvers then
check the children domain based on the delegation information, and
get the answer for the respective children domain names.
When a stub resolver sends an AQ query to the recursive resolver, the
recursive resolver may have some answers for one or more questions in
the cache, but not for all questions. Under that case, the recursive
resolver SHOULD forward this AQ query to some relative authoritative
servers for full answers instead of using the existing insufficient
cache information.
An AQ unaware responder is expected to ignore the AQ OPT of the
query, and may echo the received OPT back into additional section of
the response message.
5. Initiator Processing
An AQ aware initiator will put the main question into the question
section of the DNS query packet, and put related accompanying
questions into the related accompanying question fields of OPTION-
DATA of OPT RR. AQ-RCODE value will be sent as 111111110100 bits.
The AQ-TYPE value should be set as the query type related to
accompanying questions. The Prefix value should be set as a pointer
or a sequence of labels ending with a pointer pointing to the the
main domain name of the main question for the respective accompanying
domain name of the accompanying question.
An AQ aware initiator SHOULD set the limitation of what is the
maximum number of accompanying questions a AQ query can bring. This
document suggests that the maximum number is six since most DNS
resource records which need parallel query will not larger than six.
The implementers may set six as the defaul value in the
implementation. The responder can refuse to answer the AQ query if
the maximum number of the accompanying questions is larger than the
default maximum value, and return "not been implemented, too many
accompanying-questions." information to the initiator.
If the initial value of the AQ-RCODE is unchanged in the response or
the AQ OPT is not echo back, it indicates that the responder is AQ
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unaware. In that case, the responder will deal with the main
question only. The initiator should sent the accompanying questions
one by one via the normal DNS query. In such followup related
queries, AQ processing should probably not be attempted, to reduce
waste of network resources.
6. Query and Response Example
Example: one main question with 2 accompanying questions
The query would look like:
+---------------------------------------------------+
Header | OPCODE=SQUERY |
+---------------------------------------------------+
Question | QNAME=EXAMPLE.COM., QCLASS=IN, QTYPE=A |
+---------------------------------------------------+
Answer | |
+---------------------------------------------------+
Authority | <empty> |
+---------------------------------------------------+
Additional | |
| AQ-TYPE=AAAA,AQ-RCODE=111111110100, |
| Prefix=EXAMPLE.COM., |
| AQ-TYPE=TLSA,,AQ-RCODE=111111110100, |
| Prefix=_443._tcp.EXAMPLE.COM., |
+---------------------------------------------------+
The response from AQ aware responders would be:
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE, AA, RCODE=NOERROR |
| ANCOUNT=1, ARCOUNT=1, NSCOUNT=0 |
+---------------------------------------------------+
Question | QNAME=EXAMPLE.COM., QCLASS=IN, QTYPE=A |
+---------------------------------------------------+
Answer | example.com IN A 192.168.0.1 |
| example.com. IN AAAA 2001:cc8::1 |
| _443._tcp.example.com. IN TLSA |
| ( 3 0 0 30820307308201efa003020102020... ) |
+---------------------------------------------------+
Authority | <empty> |
+---------------------------------------------------+
Additional | |
| AQ-TYPE=AAAA, AQ-RCODE=NOERROR, AQ-ANCOUNT=1, |
| AQ-ARCOUNT=0, AQ-NSCOUNT=0, |
| Prefix=EXAMPLE.COM., |
| AQ-TYPE=TLSA, AQ-RCODE=NOERROR, AQ-ANCOUNT=1, |
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| AQ-ARCOUNT=0, AQ-NSCOUNT=0, |
| Prefix=_443._tcp.EXAMPLE.COM., |
+---------------------------------------------------+
The response from AQ unaware responders would be:
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE, AA, RCODE=NOERROR |
+---------------------------------------------------+
Question | QNAME=EXAMPLE.COM., QCLASS=IN, QTYPE=A |
+---------------------------------------------------+
Answer | example.com. IN A 192.168.0.1 |
+---------------------------------------------------+
Authority | <empty> |
+---------------------------------------------------+
Additional | |
| AQ-TYPE=AAAA,AQ-RCODE=111111110100, |
| Prefix=EXAMPLE.COM., |
| AQ-TYPE=TLSA, AQ-RCODE=111111110100, |
| Prefix=_443._tcp.EXAMPLE.COM., |
+---------------------------------------------------+
7. IANA Considerations
IANA should allocate DNS EDNS0 Option Codes (OPT) following this
document. IANA should reserve RCODE with the value of 111111110100
bits for this document.
8. Security Considerations
TBD
9. Acknowledgements
The authors thank the members in DNSOP mailing list for helpful
discussions, and especially thank Kazunori Fujiwara, JINMEI Tatuya
and Bob Harold for kind comments, suggestions and improvements for
the document. The authors also thanks Likun Zhang for helpful
discussion about some topics related to implementation.
10. Change History
RFC Editor: Please remove this section.
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10.1. draft-yao-dnsop-accompanying-questions: Version 00
o A Mechanism for DNS query including one main question with several
accompanying questions
10.2. draft-yao-dnsop-accompanying-questions: Version 01
o Simpilfy the mechanism.
10.3. draft-yao-dnsop-accompanying-questions: Version 02
o Remove the AQ and Count bits, and add AQ-ANCOUNT AQ-ARCOUNT AQ-
NSCOUNT
11. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <http://www.rfc-editor.org/info/rfc1035>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
DOI 10.17487/RFC5321, October 2008,
<http://www.rfc-editor.org/info/rfc5321>.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
2012, <http://www.rfc-editor.org/info/rfc6698>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013,
<http://www.rfc-editor.org/info/rfc6891>.
Authors' Addresses
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Jiankang Yao
CNNIC-Farsight Joint Laboratory
4 South 4th Street,Zhongguancun,Haidian District
Beijing, Beijing 100190
China
Phone: +86 10 5881 3007
Email: yaojk@cnnic.cn
Paul Vixie
CNNIC-Farsight Joint Laboratory
4 South 4th Street,Zhongguancun,Haidian District
Beijing, Beijing 100190
China
Phone: +1 650 489 7919
Email: vixie@fsi.io
Ning Kong
CNNIC
4 South 4th Street,Zhongguancun,Haidian District
Beijing, Beijing 100190
China
Phone: +86 10 5881 3147
Email: nkong@cnnic.cn
Xiaodong Li
CNNIC
4 South 4th Street,Zhongguancun,Haidian District
Beijing, Beijing 100190
China
Phone: +86 10 5881 3020
Email: xl@cnnic.cn
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