Internet DRAFT - draft-yao-dnsop-accompanying-questions
draft-yao-dnsop-accompanying-questions
dnsop J. Yao
Internet-Draft P. Vixie
Intended status: Standards Track CNNIC-Farsight Joint Laboratory
Expires: March 21, 2018 N. Kong
X. Li
CNNIC
September 17, 2017
A DNS Query including A Main Question with Accompanying Questions
draft-yao-dnsop-accompanying-questions-04
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 extension enables a range of initiators to look up
"X, or failing that, Y" in a better way than both current
alternatives. This mechanism can reduce the number of DNS round-
trips per application work-unit.
Status of This Memo
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This Internet-Draft will expire on March 21, 2018.
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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 . . . . . . . . . . . . . . . . . . . . 6
5. Initiator Processing . . . . . . . . . . . . . . . . . . . . 7
6. Query and Response Example . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
10. Change History . . . . . . . . . . . . . . . . . . . . . . . 9
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
10.4. draft-yao-dnsop-accompanying-questions: Version 03 . . . 10
10.5. draft-yao-dnsop-accompanying-questions: Version 04 . . . 10
11. Normative References . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Sometimes, when DNS lookup of X, an application will lookup Y if X
fails. For examples, the initiator may fall back to A record if the
lookup of MX record fails.
Some initiators do it in sequence, X and after a few seconds, then Y.
Although it is simple, this leads to unpleasant waiting whenever X
times out or answers negatively.
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Some initiators use concurrent X/Y lookups and a state machine to
decide whether to use X or Y. If an answer to Y arrives but none to
X, the initiator needs to wait a little or else fall back to Y
inappropriately. Concurrent lookup is faster if the X lookup takes
time and falling back to Y is appropriate, but rather complex, with
four states to test, and the initiator needs to wait for an answer to
X or a timeout before it can use Y.
This document enables a quicker, more easily tested failover. There
is no need to test different answer sequences, there's no need for a
state machine, there's no need for timeouts beyond receiving the
reply. 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. It has the
following advantages compared to other solutions.
o Compared to sequential lookups: It's roughly as simple, but much
faster in case a fallback to Y is necessary.
o Compared to the concurrent mechanism: It is slightly faster (if
the initiator needs to wait for an X timeout) and/or prevents
inappropriate fallback (if the answer to X arrives too late), and
it has a simpler state machine.
This mechanism can also be used in the scenarios when the application
needs more records of the same domain name or its sub-domain name.
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].
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].
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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 6 accompanying questions with AQ-RCODE.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| Reserved | AQ-RCODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-TYPE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-ANCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-NSCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-ARCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| |
/ Prefix /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| Reserved | AQ-RCODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-TYPE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-ANCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-NSCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-ARCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
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| |
/ Prefix /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| Reserved | AQ-RCODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-TYPE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-ANCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-NSCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| AQ-ARCOUNT |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| |
/ Prefix /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| |
/ ...... /
/ /
o Reserved field is kept for the future use.
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.
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o Prefix field indicates a domain name with the form of a dot 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 and its accompanying questions. Since the value for the
accompanying questions' ANCOUNT, NSCOUNT and ARCOUNT can be known
from the respective value of AQ-ANCOUNT, AQ-NSCOUNT and AQ-ARCOUNT,
the actual value of the main question's ANCOUNT, NSCOUNT and ARCOUNT
can be calculated from the ANCOUNT, NSCOUNT and ARCOUNT in the DNS
response header. When the answer is negative for the accompanying
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. If some DNS resource records
are needed to be processed at the same time, the DNS administrator
may configure it together. 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
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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 each accompanying question
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 dot 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
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 |
+---------------------------------------------------+
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Answer | |
+---------------------------------------------------+
Authority | <empty> |
+---------------------------------------------------+
Additional | |
| AQ-TYPE=AAAA,AQ-RCODE=111111110100, |
| Prefix=., |
| AQ-TYPE=TLSA,,AQ-RCODE=111111110100, |
| Prefix=_443._tcp., |
+---------------------------------------------------+
The response from AQ aware responders would be:
+---------------------------------------------------+
Header | OPCODE=SQUERY, RESPONSE, AA, RCODE=NOERROR |
| ANCOUNT=3, 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=., |
| AQ-TYPE=TLSA, AQ-RCODE=NOERROR, AQ-ANCOUNT=1, |
| AQ-ARCOUNT=0, AQ-NSCOUNT=0, |
| Prefix=_443._tcp., |
+---------------------------------------------------+
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 | |
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| AQ-TYPE=AAAA,AQ-RCODE=111111110100, |
| Prefix=., |
| AQ-TYPE=TLSA, AQ-RCODE=111111110100, |
| Prefix=_443._tcp., |
+---------------------------------------------------+
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,
Bob Harold, Arnt Gulbrandsen, Olafur Gudmundsson and Stephane
Bortzmeyer 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.
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
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10.4. draft-yao-dnsop-accompanying-questions: Version 03
o Improve the introduction and explains the motivation of this draft
10.5. draft-yao-dnsop-accompanying-questions: Version 04
o Improve the document
11. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[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>.
[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>.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
DOI 10.17487/RFC5321, October 2008,
<https://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, <https://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,
<https://www.rfc-editor.org/info/rfc6891>.
Authors' Addresses
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
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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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