Network Working Group P. Hoffman
Internet-Draft ICANN
Intended status: Experimental March 07, 2016
Expires: September 8, 2016
Representing DNS Messages in JSON
draft-hoffman-dns-in-json-06
Abstract
Some applications use DNS messages, or parts of DNS messages, as
data. For example, a system that captures DNS queries and responses
might want to be able to easily search those without having to decode
the messages each time. Another example is a system that puts
together DNS queries and responses from message parts. This document
describes a standardized format for DNS message data in JSON.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 8, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
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include Simplified BSD License text as described in Section 4.e 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 . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Design of the Format . . . . . . . . . . . . . . . . . . 3
2. JSON Format for DNS Messages . . . . . . . . . . . . . . . . 4
2.1. Message Object Members . . . . . . . . . . . . . . . . . 4
2.2. Resource Record Object Members . . . . . . . . . . . . . 5
2.3. The Message and Its Parts as Octets . . . . . . . . . . . 6
2.4. Additional Message Object Members . . . . . . . . . . . . 6
2.5. Name Fields . . . . . . . . . . . . . . . . . . . . . . . 7
3. JSON Format for a Paired DNS Query and Response . . . . . . . 7
4. Streaming DNS Objects . . . . . . . . . . . . . . . . . . . . 7
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Example of the Format of a DNS Query . . . . . . . . . . 7
5.2. Example of the Format of a Paired DNS Query and Response 8
6. Local Format Policy . . . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
The DNS message format is defined in [RFC1035]. DNS queries and DNS
responses have exactly the same structure. Many of the field names
and data type names given in [RFC1035] are commonly used in
discussions of DNS. For example, it is common to hear things like
"the query had a QNAME of 'example.com'" or "the RDATA has a simple
structure".
There are hundreds of data interchange formats for serializing
structured data. Currently, JSON [RFC7159] is quite popular for many
types of data, particularly data that has named sub-fields and
optional parts.
This document uses JSON to describe DNS messages. It also defines
how to describe a paired DNS query and response, and how to stream
DNS objects.
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1.1. Design of the Format
There are many ways to design a data format. This document uses a
specific design methodology based on the DNS format.
o The format is based on JSON objects in order to allow a writer to
include or exclude parts of the format at will. No object members
are ever required.
o This format is purposely overly-general. Protocols and
applications that use this format are expected to use only a
subset of the items defined here.
o All values that are eight bits or shorter (even booleans) are
represented by JSON integers.
o The encoding for the DNS object is ASCII as described in
[RFC0020]. This is done to prevent an attempt to use a different
encoding such as UTF-8 for octets in names or data.
o Values for domain names and RDATA can be expressed using the
decimal escaping ("\DDD") defined in [RFC1035].
o Names of items that have string values can have an "*" or "!"
appended to them to indicate a non-ASCII encoding of the value.
Names that end in "*" have values stored in base16 encoding (hex
with uppercase letters) defined in [RFC4648]. This is
particularly useful for RDATA that is binary. Names that end in
"!" have values stored in base64url encoding defined in [RFC4648].
This is particularly useful for RDATA that very long (such as
cryptographic keys) or entire records.
o All field names used in [RFC1035] are used in this format as-is.
Names not defined in [RFC1035] use "camel case" with the first
letter lowercase.
o The same data may be represented in multiple object members
multiple times. For example, there is a member for the octets of
the DNS message header, and there are members for each named part
of the header. A message object can thus inadvertently have
inconsistent data, such as a header member whose value does not
match the value of the first bits in the entire message member.
o The design explicitly allows for the description of malformed DNS
messages. This is important for systems that are logging messages
seen on the wire, particularly messages that might be used as part
of an attack. For example, an RR might have an RDLENGTH of 4 but
an RDATA whose length is longer than 4 (if it is the last RR in a
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message); a DNS message whose QDCOUNT is 0; a DNS message whose
length is less than 12 octets, meaning it doesn't even have a full
header; and so on.
o An object in this format can have zero or more of the members
defined here; that is, no members are required by the format
itself. Instead, profiles that use this format might have
requirements for mandatory members, optional members, and
prohibited members from the format. Also, this format does not
prohibit members that are not defined in this format; profiles of
the format are free to add new members in the profile.
This document defines DNS messages, not zone files. A later
specification could be written to extend it to represent zone files.
2. JSON Format for DNS Messages
The following gives all of the members defined for a DNS message. It
is organized approximately by levels of the DNS message.
2.1. Message Object Members
o ID - Integer whose value is 0 to 65535
o QR - Integer whose value is 0 or 1
o Opcode - Integer whose value is 0 to 15
o AA - Integer whose value is 0 or 1
o TC - Integer whose value is 0 or 1
o RD - Integer whose value is 0 or 1
o RA - Integer whose value is 0 or 1
o AD - Integer whose value is 0 or 1
o CD - Integer whose value is 0 or 1
o RCODE - Integer whose value is 0 to 15
o QDCOUNT - Integer whose value is 0 to 65535
o ANCOUNT - Integer whose value is 0 to 65535
o NSCOUNT - Integer whose value is 0 to 65535
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o ARCOUNT - Integer whose value is 0 to 65535
o QNAME - String of the name of the first Question section of the
message; see Section 2.5 for a desciption of the contents
o compressedQNAME - The octets of the name of the first Questing
section of the message before removing [RFC1035] name compression
o QTYPE - Integer whose value is 0 to 65535, of the QTYPE of the
first Question section of the message
o QCLASS - Integer whose value is 0 to 65535, of the QCLASS of the
first Question section of the message
o questionRRs - Array of zero or more resource records in the
Question section
o answerRRs - Array of zero or more resource records in the Answer
section
o authorityRRs - Array of zero or more resource records in the
Authority section
o additionalRRs - Array of zero or more resource records in the
Additional section
2.2. Resource Record Object Members
A resource record is represented as an object with the following
members.
o NAME - String of the NAME field of the resource record; see
Section 2.5 for a description of the contents
o compressedNAME - String of the octets of the NAME field before
removing [RFC1035] name compression
o TYPE - String whose value is from the IANA RR TYPEs registry, or
that has the format in [RFC3597]
o CLASS - String whose value is from the IANA DNS CLASSes registry,
or that has the format in [RFC3597]
o TTL - Integer whose value is 0 to 4294967295
o RDLENGTH - Integer whose value is 0 to 65535. Applications using
this format are unlikely to use this value directly, and instead
calculate the value from the RDATA.
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o RDATA - String of the octets of the RDATA field of the resource
record. This will most likely be given as RDATA* or RDATA!, not
as an ASCII string with \DDD encoding. (This format does not have
a way of expressing RDATA by the fields for each DNS record type.
Instead, it assumes that a processor of these records probably
already knows how to split up an RDATA using master file format.)
A Question section can be expressed as a resource record. When doing
so, the TTL, RDLENGTH, and RDATA members make no sense.
2.3. The Message and Its Parts as Octets
The following can be members of a message object. These names will
most likely be given as "*" or "!" to indicate encoding that is not
plain ASCII. All these items are strings.
o messageOctets - The octets of the message
o headerOctets - The first 12 octets of the message (or fewer, if
the message is truncated)
o questionOctets - The octets of the Question section
o answerOctets - The octets of the Answer section
o authorityOctets - The octets of the Authority section
o additionalOctets - The octets of the Additional section
The following can be a member of a resource record object.
o rrOctets - The octets of a particular resource record
The items in this section are useful in applications to canonically
reproduce what appeared on the wire. For example, an application
that is converting wire-format requests and responses might do
decompression of names, but the system reading the converted data may
want to be sure the decompression was done correctly. Such a system
would need to see the part of the message where the decompressed
labels resided, such as in one of the items in this section.
2.4. Additional Message Object Members
The following are members that might appear in a message object:
o dateString - The date that the message was sent or received, given
as a string in the standard format described in [RFC3339], as
refined by Section 3.3 of [RFC4287]
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o dateSeconds - The date that the message was sent or received,
given as the number of seconds since 1970-01-01T00:00Z in UTC
time; this number can be fractional
o comment - An unstructured comment as a string
2.5. Name Fields
Names are represented by JSON strings. The rules for how names are
encoded are described in Section 1.1. The contents of these fields
are always uncompressed, that is after [RFC1035] name compression has
been removed.
There are three encodings for names:
o If the member name does not end in "*" or "!", the value is a
domain name encoded as ASCII. non-ASCII octets in the domain name
can be expressed using the decimal escaping ("\DDD"). Periods
indicate separation between labels.
o If the member name ends in "*", the value is the wire format for
an entire domain name stored in base16 encoding.
o If the member name ends in "!", the value is the wire format for
an entire domain name stored in base64url encoding.
3. JSON Format for a Paired DNS Query and Response
A paired DNS query and response is represented as an object. Two
optional members of this object are names "queryRecord" and
"responseRecord", and each has a value that is an message object.
This design was chosen (as compared to the more obvious array of two
values) so that a paired DNS query and response could be
differentiated from a stream of DNS messages whose length happens to
be two.
4. Streaming DNS Objects
Streaming DNS objects is performed using [RFC7464].
5. Examples
5.1. Example of the Format of a DNS Query
The following is an example of a query for the A record of
example.com.
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{ "ID": 19678, "QR": 0, "Opcode": 0,
"AA": 0, "TC": 0, "RD": 0, "RA": 0, "AD": 0, "CD": 0, "RCODE": 0,
"QDCOUNT": 1, "ANCOUNT": 0, "NSCOUNT": 0, "ARCOUNT": 0,
"QNAME": "example.com", "QTYPE": 1, "QCLASS": 1
}
As stated earlier, all members of an object are optional. This
example object could have one or more of the following members as
well:
"answerRRs": []
"authorityOctets*": ""
"comment": "Something pithy goes here"
"dateSeconds": 1408504748.657783
"headerOctets*": "4CDE00000001000000000000"
"QNAME*": "076578616D706C6503636F6D00",
"messageOctets*":
"4CDE00000001000000000000076578616D706C6503636F6D0000010001"
"messageOctets!": "TN4AAAABAAAAAAAAB2V4YW1wbGUDY29tAAABAAE="
"questionOctets*": "076578616D706C6503636F6D0000010001"
"questionRRs": [ { "NAME*": "076578616D706C6503636F6D00", "TYPE": 1,
"CLASS": 1, "hostNAME" : "example.com." } ]
"questionRRs": [ { "NAME": "example.com.", "TYPE": 1,
"CLASS": 1, } ]
5.2. Example of the Format of a Paired DNS Query and Response
The following is a paired DNS query and response for a query for the
A record of example.com.
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{
"queryRecord": { "ID": 32784, "QR": 0, "Opcode": 0, "AA": 0,
"TC": 0, "RD": 0, "RA": 0, "AD": 0, "CD": 0,
"RCODE": 0, "QDCOUNT": 1, "ANCOUNT": 0,
"NSCOUNT": 0, "ARCOUNT": 0,
"QNAME": "example.com.",
"QTYPE": 1, "QCLASS": 1 },
"responseRecord": { "ID": 32784, "QR": 1, "AA": 1, "RCODE": 0,
"QDCOUNT": 1, "ANCOUNT": 1, "NSCOUNT": 1,
"ARCOUNT": 0,
"answerRRs": [ { "NAME": "example.com.",
"TYPE": 1, "CLASS": 1,
"TTL": 3600, "RDLENGTH": 4,
"RDATA*": "16212C37" } ],
"authorityRRs": [ { "NAME": "ns.example.com.",
"TYPE": 1, "CLASS": 1,
"TTL": 28800,
"RDLENGTH": 4,
"RDATA*": "A5E3F903" } ]
}
}
6. Local Format Policy
Systems using this format in this document will likely have policy
about what must be in the objects. Those policies are outside the
scope of this document.
For example, private DNS systems such as those described in
[I-D.dulaunoy-kaplan-passive-dns-cof] covers just DNS responses.
Such a system might have a policy that makes QNAME, QTYPE, and
answerRRs mandatory. That document also describes two mandatory
times that are not in this format, so the policy would possibly also
define those members and make them mandatory. The policy could also
define additional members that might appear in a record.
As another example, a program that uses this format for configuring
what a test client sends on the wire might have a policy of "each
record object can have as few members as it wants; all unstated
members are filled in from previous records".
7. IANA Considerations
This document has no effect on IANA registries.
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8. Security Considerations
As described in Section 1.1, a message object can have inconsistent
data, such as a message with an ANCOUNT of 1 but that has either an
empty answerRRs array or an answerRRs array that has 2 or more RRs.
Other examples of inconsistent data would be resource records whose
RDLENGTH does not match the length of the decoded value in the RDATA*
member, or a record whose various header fields do not match the
value in headerOctets*, and so on. A reader of this format must
never assume that all of the data in an object are all consistent
with each other.
Numbers in JSON do not have any bounds checking. Thus, integer
values in a record might have invalid values, such as an ID value
that is negative, or greater than or equal to 2^16, or has a
fractional part.
9. Acknowledgements
Some of the ideas in this document were inspired by
[I-D.dulaunoy-kaplan-passive-dns-cof]. The document was also
inspired by early ideas from Stephane Bortzmeyer. There was earlier,
abandoned work on encoding DNS messages in XML ([I-D.daley-dnsxml]
and [I-D.mohan-dns-query-xml], to name just two).
10. References
10.1. Normative References
[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>.
[RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record
(RR) Types", RFC 3597, DOI 10.17487/RFC3597, September
2003, <http://www.rfc-editor.org/info/rfc3597>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <http://www.rfc-editor.org/info/rfc7159>.
[RFC7464] Williams, N., "JavaScript Object Notation (JSON) Text
Sequences", RFC 7464, DOI 10.17487/RFC7464, February 2015,
<http://www.rfc-editor.org/info/rfc7464>.
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10.2. Informative References
[I-D.daley-dnsxml]
Daley, J., Morris, S., and J. Dickinson, "dnsxml - A
standard XML representation of DNS data", draft-daley-
dnsxml-00 (work in progress), July 2013.
[I-D.dulaunoy-kaplan-passive-dns-cof]
Dulaunoy, A., Kaplan, A., Vixie, P., and H. Stern,
"Passive DNS - Common Output Format", draft-dulaunoy-
kaplan-passive-dns-cof-02 (work in progress), March 2014.
[I-D.mohan-dns-query-xml]
Parthasarathy, M. and P. Vixie, "Representing DNS messages
using XML", draft-mohan-dns-query-xml-00 (work in
progress), September 2011.
[RFC0020] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969,
<http://www.rfc-editor.org/info/rfc20>.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
<http://www.rfc-editor.org/info/rfc3339>.
[RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom
Syndication Format", RFC 4287, DOI 10.17487/RFC4287,
December 2005, <http://www.rfc-editor.org/info/rfc4287>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<http://www.rfc-editor.org/info/rfc4648>.
Author's Address
Paul Hoffman
ICANN
Email: paul.hoffman@icann.org
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