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Domain Name System Operations A. Dulaunoy
Internet-Draft CIRCL
Intended status: Informational A. Kaplan
Expires: May 16, 2016 CERT.at
P. Vixie
H. Stern
Farsight Security, Inc.
November 13, 2015
Passive DNS - Common Output Format
draft-dulaunoy-dnsop-passive-dns-cof-01
Abstract
This document describes a common output format of Passive DNS Servers
which clients can query. The output format description includes also
in addition a common semantic for each Passive DNS system. By having
multiple Passive DNS Systems adhere to the same output format for
queries, users of multiple Passive DNS servers will be able to
combine result sets easily.
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-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on May 16, 2016.
Copyright Notice
Copyright (c) 2015 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
publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Limitation . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Common Output Format . . . . . . . . . . . . . . . . . . . . 3
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. ABNF grammar . . . . . . . . . . . . . . . . . . . . . . 4
3.3. Mandatory Fields . . . . . . . . . . . . . . . . . . . . 4
3.3.1. rrname . . . . . . . . . . . . . . . . . . . . . . . 5
3.3.2. rrtype . . . . . . . . . . . . . . . . . . . . . . . 5
3.3.3. rdata . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3.4. time_first . . . . . . . . . . . . . . . . . . . . . 5
3.3.5. time_last . . . . . . . . . . . . . . . . . . . . . . 6
3.4. Optional Fields . . . . . . . . . . . . . . . . . . . . . 6
3.4.1. count . . . . . . . . . . . . . . . . . . . . . . . . 6
3.4.2. bailiwick . . . . . . . . . . . . . . . . . . . . . . 6
3.5. Additional Fields . . . . . . . . . . . . . . . . . . . . 6
3.5.1. sensor_id . . . . . . . . . . . . . . . . . . . . . . 6
3.5.2. zone_time_first . . . . . . . . . . . . . . . . . . . 6
3.5.3. zone_time_last . . . . . . . . . . . . . . . . . . . 7
3.5.4. origin . . . . . . . . . . . . . . . . . . . . . . . 7
3.6. Additional Fields Registry . . . . . . . . . . . . . . . 7
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. References . . . . . . . . . . . . . . . . . . . . . . . 9
8.3. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Passive DNS is a technique described by Florian Weimer in 2005 in
Passive DNS replication, F Weimer - 17th Annual FIRST Conference on
Computer Security [WEIMERPDNS]. Since then multiple Passive DNS
implementations were created and evolved over time. Users of these
Passive DNS servers may query a server (often via WHOIS [RFC3912] or
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HTTP REST [REST]), parse the results and process them in other
applications.
There are multiple implementations of Passive DNS software. Users of
passive DNS query each implementation and aggregate the results for
their search. This document describes the output format of four
Passive DNS Systems ([DNSDB], [PDNSCERTAT], [PDNSCIRCL] and
[PDNSCOF]) which are in use today and which already share a nearly
identical output format. As the format and the meaning of output
fields from each Passive DNS need to be consistent, we propose in
this document a solution to commonly name each field along with their
corresponding interpretation. The format follows a simple key-value
structure in JSON [RFC4627] format. The benefit of having a
consistent Passive DNS output format is that multiple client
implementations can query different servers without having to have a
separate parser for each individual server. passivedns-client
[PDNSCLIENT] currently implements multiple parsers due to a lack of
standardization. The document does not describe the protocol (e.g.
WHOIS [RFC3912], HTTP REST [REST]) nor the query format used to query
the Passive DNS. Neither does this document describe "pre-recursor"
Passive DNS Systems. Both of these are separate topics and deserve
their own RFC document.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Limitation
As a Passive DNS servers can include protection mechanisms for their
operation, results might be different due to those protection
measures. These mechanisms filter out DNS answers if they fail some
criteria. The bailiwick algorithm [BAILIWICK] protects the Passive
DNS Database from cache poisoning attacks [CACHEPOISONING]. Another
limitation that clients querying the database need to be aware of is
that each query simply gets a snapshot-answer of the time of
querying. Clients MUST NOT rely on consistent answers. Nor must
they assume that answers must be identical across multiple Passive
DNS Servers.
3. Common Output Format
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3.1. Overview
The formatting of the answer follows the JSON [RFC4627] format. In
fact, it is a subset of the full JSON language. Notable differences
are the modified definition of whitespace ("ws"). The order of the
fields is not significant for the same resource type.
The intent of this output format is to be easily parsable by scripts.
Each JSON object is expressed on a single line to be processed by the
client line-by-line. Every implementation MUST support the JSON
output format.
Examples of JSON (Appendix A) output are in the appendix.
3.2. ABNF grammar
Formal grammar as defined in ABNF [RFC2234]
answer = entries
entries = * ( entry CR)
entry = "{" keyvallist "}"
keyvallist = [ member *( value-separator member ) ]
member = qm field qm name-separator value
name-separator = ws %x3A ws ; a ":" colon
value = value ; as defined in the JSON RFC
value-separator = ws %x2C ws ; , comma. As defined in JSON
field = "rrname" | "rrtype" | "rdata" | "time_first" |
"time_last" | "count" | "bailiwick" | "sensor_id" |
"zone_time_first" | "zone_time_last" | futureField
futureField = string
CR = %x0D
qm = %x22 ; " a quotation mark
ws = *(
%x20 | ; Space
%x09 ; Horizontal tab
)
Note that value is defined in JSON [RFC4627] and has the exact same
specification as there. The same goes for the definition of string.
3.3. Mandatory Fields
Implementation MUST support all the mandatory fields.
Uniqueness property: the tuple (rrname,rrtype,rdata) will always be
unique within one answer per server. While rrname and rrtype are
always individual JSON primitive types (strings, numbers, booleans or
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null), rdata MAY return multiple resource records or a single record.
When multiple resource records are returned, rdata MUST be a JSON
array. In the case of a single resource record is returned, rdata
MUST be a JSON string.
3.3.1. rrname
This field returns the name of the queried resource.
3.3.2. rrtype
This field returns the resource record type as seen by the passive
DNS. The key is rrtype and the value is in the interpreted record
type represented as a JSON [RFC4627] string. If the value cannot be
interpreted the decimal value is returned following the principle of
transparency as described in RFC 3597 [RFC3597]. Then the decimal
value is represented as a JSON [RFC4627] number. The resource record
type can be any values as described by IANA in the DNS parameters
document in the section 'Resource Record (RR) TYPEs'
(http://www.iana.org/assignments/dns-parameters). Currently known
and supported textual descriptions of rrtypes are: A, AAAA, CNAME,
PTR, SOA, TXT, DNAME, NS, SRV, RP, NAPTR, HINFO, A6. A client MUST
be able to understand these textual rrtype values represented as a
JSON [RFC4627] string. In addition, a client MUST be able to handle
a decimal value (as mentioned above) as answer represented as a JSON
[RFC4627] number.
3.3.3. rdata
This field returns the resource records of the queried resource.
When multiple resource records are returned, rdata MUST be a JSON
array. In the case of a single resource record is returned, rdata
MUST be a JSON string. Each resource record is represented as a JSON
[RFC4627] string. Each resource record MUST be escaped as defined in
section 2.6 of RFC4627 [RFC4627]. Depending on the rrtype, this can
be an IPv4 or IPv6 address, a domain name (as in the case of CNAMEs),
an SPF record, etc. A client MUST be able to interpret any value
which is legal as the right hand side in a DNS master file RFC 1035
[RFC1035] and RFC 1034 [RFC1034]. If the rdata came from an unknown
DNS resource records, the server must follow the transparency
principle as described in RFC 3597 [RFC3597].
3.3.4. time_first
This field returns the first time that the record / unique tuple
(rrname, rrtype, rdata) has been seen by the passive DNS. The date
is expressed in seconds (decimal) since 1st of January 1970 (Unix
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timestamp). The time zone MUST be UTC. This field is represented as
a JSON [RFC4627] number.
3.3.5. time_last
This field returns the last time that the unique tuple (rrname,
rrtype, rdata) record has been seen by the passive DNS. The date is
expressed in seconds (decimal) since 1st of January 1970 (Unix
timestamp). The time zone MUST be UTC. This field is represented as
a JSON [RFC4627] number.
3.4. Optional Fields
Implementations SHOULD support one or more fields.
3.4.1. count
Specifies how many authoritative DNS answers were received at the
Passive DNS Server's collectors with exactly the given set of values
as answers (i.e. same data in the answer set - compare with the
uniqueness property in "Mandatory Fields"). The number of requests
is expressed as a decimal value. This field is represented as a JSON
[RFC4627] number.
3.4.2. bailiwick
The bailiwick is the best estimate of the apex of the zone where this
data is authoritative.
3.5. Additional Fields
Implementations MAY support the following fields:
3.5.1. sensor_id
This field returns the sensor information where the record was seen.
It is represented as a JSON [RFC4627] string.
3.5.2. zone_time_first
This field returns the first time that the unique tuple (rrname,
rrtype, rdata) record has been seen via master file import. The date
is expressed in seconds (decimal) since 1st of January 1970 (Unix
timestamp). The time zone MUST be UTC. This field is represented as
a JSON [RFC4627] number.
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3.5.3. zone_time_last
This field returns the last time that the unique tuple (rrname,
rrtype, rdata) record has been seen via master file import. The date
is expressed in seconds (decimal) since 1st of January 1970 (Unix
timestamp). The time zone MUST be UTC. This field is represented as
a JSON [RFC4627] number.
3.5.4. origin
Specifies the resource origin of the Passive DNS response. This
field is represented as a Uniform Resource Identifier [RFC3986]
(URI).
3.6. Additional Fields Registry
In accordance with [RFC6648], designers of new passive DNS
applications that would need additional fields can request and
register new field name at https://github.com/adulau/pdns-qof/wiki/
Additional-Fields.
4. Acknowledgements
Thanks to the Passive DNS developers who contributed to the document.
5. IANA Considerations
This memo includes no request to IANA.
6. Privacy Considerations
Passive DNS Servers capture DNS answers from multiple collecting
points ("sensors") which are located on the Internet-facing side of
DNS recursors ("post-recursor passive DNS"). In this process, they
intentionally omit the source IP, source port, destination IP and
destination port from the captured packets. Since the data is
captured "post-recursor", the timing information (who queries what)
is lost, since the recursor will cache the results. Furthermore,
since multiple sensors feed into a passive DNS server, the resulting
data gets mixed together, reducing the likelihood that Passive DNS
Servers are able to find out much about the actual person querying
the DNS records nor who actually sent the query. In this sense,
passive DNS Servers are similar to keeping an archive of all previous
phone books - if public DNS records can be compared to phone numbers
- as they often are. Nevertheless, the authors strongly encourage
Passive DNS implementors to take special care of privacy issues.
bortzmeyer-dnsop-dns-privacy is an excellent starting point for this.
Finally, the overall recommendations in RFC6973 [RFC6973] should be
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taken into consideration when designing any application which uses
Passive DNS data.
7. Security Considerations
In some cases, Passive DNS output might contain confidential
information and its access might be restricted. When a user is
querying multiple Passive DNS and aggregating the data, the
sensitivity of the data must be considered.
8. References
8.1. 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>.
[RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, DOI 10.17487/RFC2234,
November 1997, <http://www.rfc-editor.org/info/rfc2234>.
[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>.
[RFC3912] Daigle, L., "WHOIS Protocol Specification", RFC 3912,
DOI 10.17487/RFC3912, September 2004,
<http://www.rfc-editor.org/info/rfc3912>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>.
[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627,
DOI 10.17487/RFC4627, July 2006,
<http://www.rfc-editor.org/info/rfc4627>.
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[RFC5001] Austein, R., "DNS Name Server Identifier (NSID) Option",
RFC 5001, DOI 10.17487/RFC5001, August 2007,
<http://www.rfc-editor.org/info/rfc5001>.
[RFC6648] Saint-Andre, P., Crocker, D., and M. Nottingham,
"Deprecating the "X-" Prefix and Similar Constructs in
Application Protocols", BCP 178, RFC 6648,
DOI 10.17487/RFC6648, June 2012,
<http://www.rfc-editor.org/info/rfc6648>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<http://www.rfc-editor.org/info/rfc6973>.
8.2. References
[BAILIWICK]
"Passive DNS Hardening", 2010,
<https://archive.farsightsecurity.com/Passive_DNS/
passive_dns_hardening_handout.pdf>.
[CACHEPOISONING]
"Black ops 2008: It's the end of the cache as we know
it.", 2008, <http://kurser.lobner.dk/dDist/DMK_BO2K8.pdf>.
[DNSDB] "DNSDB API", 2013, <https://api.dnsdb.info/>.
[PDNSCERTAT]
"pDNS presentation at 4th Centr R&D workshop Frankfurt Jun
5th 2012", 2012,
<http://www.centr.org/system/files/agenda/attachment/
rd4-papst-passive_dns.pdf>.
[PDNSCIRCL]
"CIRCL Passive DNS", 2012, <https://www.circl.lu/services/
passive-dns/>.
[PDNSCLIENT]
"Queries 5 major Passive DNS databases: BFK, CERTEE,
DNSParse, ISC, and VirusTotal.", 2013,
<https://github.com/chrislee35/passivedns-client>.
[PDNSCOF] "Passive DNS server interface using the common output
format", 2013, <https://github.com/adulau/pdns-qof-
server/>.
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[REST] "Representational State Transfer (REST)", 2000,
<http://www.ics.uci.edu/~fielding/pubs/dissertation/
rest_arch_style.htm>.
[WEIMERPDNS]
"Passive DNS Replication", 2005,
<http://www.enyo.de/fw/software/dnslogger/
first2005-paper.pdf>.
8.3. Informative References
[I-D.narten-iana-considerations-rfc2434bis]
Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", draft-narten-iana-
considerations-rfc2434bis-09 (work in progress), March
2008.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<http://www.rfc-editor.org/info/rfc3552>.
Appendix A. Examples
The JSON output are represented on multiple lines for readability but
each JSON object should on a single line.
If you query a passive DNS for the rrname www.ietf.org, the passive
dns common output format can be:
{"count": 102, "time_first": 1298412391, "rrtype": "AAAA",
"rrname": "www.ietf.org", "rdata": "2001:1890:1112:1::20",
"time_last": 1302506851}
{"count": 59, "time_first": 1384865833, "rrtype": "A",
"rrname": "www.ietf.org", "rdata": "4.31.198.44",
"time_last": 1389022219}
If you query a passive DNS for the rrname ietf.org, the passive dns
common output format can be:
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{"count": 109877, "time_first": 1298398002, "rrtype": "NS",
"rrname": "ietf.org", "rdata": "ns1.yyz1.afilias-nst.info",
"time_last": 1389095375}
{"count": 4, "time_first": 1298495035, "rrtype": "A",
"rrname": "ietf.org", "rdata": "64.170.98.32",
"time_last": 1298495035}
{"count": 9, "time_first": 1317037550, "rrtype": "AAAA",
"rrname": "ietf.org", "rdata": "2001:1890:123a::1:1e",
"time_last": 1330209752}
Please note that in the examples above, any backslashes "\" can be
ignored and are an artefact of the tools which produced this
document.
Authors' Addresses
Alexandre Dulaunoy
CIRCL
41, avenue de la gare
Luxembourg L-1611
Luxembourg
Phone: (+352) 247 88444
Email: alexandre.dulaunoy@circl.lu
URI: http://www.circl.lu/
L. Aaron Kaplan
CERT.at
Karlsplatz 1/2/9
Vienna A-1010
Austria
Phone: +43 1 5056416 78
Email: kaplan@cert.at
URI: http://www.cert.at/
Paul Vixie
Farsight Security, Inc.
11400 La Honda Road
Woodside, California 94062
U.S.A.
Email: paul@redbarn.org
URI: https://www.farsightsecurity.com/
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Henry Stern
Farsight Security, Inc.
11400 La Honda Road
Woodside, California 94062
U.S.A.
Phone: +1 650 542-7836
Email: henry@stern.ca
URI: https://www.farsightsecurity.com/
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<?rfc symrefs="yes"?>
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<?rfc sortrefs="yes" ?>
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<?rfc compact="yes" ?>
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<?rfc subcompact="no" ?>
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<rfc category="info" docName="draft-dulaunoy-dnsop-passive-dns-cof-01" ipr="trust200902">
<!-- category values: std, bcp, info, exp, and historic
ipr values: full3667, noModification3667, noDerivatives3667
you can add the attributes updates="NNNN" and obsoletes="NNNN"
they will automatically be output with "(if approved)" -->
<!-- ***** FRONT MATTER ***** -->
<front>
<title abbrev="Passive DNS - Common Output Format">Passive DNS - Common Output Format</title>
<author fullname="Alexandre Dulaunoy" initials="A."
surname="Dulaunoy">
<organization>CIRCL</organization>
<address>
<postal>
<street>41, avenue de la gare</street>
<city>Luxembourg</city>
<region></region>
<code>L-1611</code>
<country>Luxembourg</country>
</postal>
<phone>(+352) 247 88444</phone>
<email>alexandre.dulaunoy@circl.lu</email>
<uri>http://www.circl.lu/</uri>
<!-- uri and facsimile elements may also be added -->
</address>
</author>
<author fullname="L. Aaron Kaplan" initials="A."
surname="Kaplan">
<organization>CERT.at</organization>
<address>
<postal>
<street>Karlsplatz 1/2/9</street>
<city>Vienna</city>
<region></region>
<code>A-1010</code>
<country>Austria</country>
</postal>
<phone>+43 1 5056416 78</phone>
<email>kaplan@cert.at</email>
<uri>http://www.cert.at/</uri>
</address>
</author>
<author fullname="Paul Vixie" initials="P."
surname="Vixie">
<organization>Farsight Security, Inc.</organization>
<address>
<postal>
<street>11400 La Honda Road</street>
<city>Woodside</city>
<region>California</region>
<code>94062</code>
<country>U.S.A.</country>
</postal>
<phone></phone>
<email>paul@redbarn.org</email>
<uri>https://www.farsightsecurity.com/</uri>
</address>
</author>
<author fullname="Henry Stern" initials="H." surname="Stern">
<organization>Farsight Security, Inc.</organization>
<address>
<postal>
<street>11400 La Honda Road</street>
<city>Woodside</city>
<region>California</region>
<code>94062</code>
<country>U.S.A.</country>
</postal>
<phone>+1 650 542-7836</phone>
<email>henry@stern.ca</email>
<uri>https://www.farsightsecurity.com/</uri>
</address>
</author>
<date month="November" year="2015" />
<area>General</area>
<workgroup>Domain Name System Operations</workgroup>
<keyword>dns</keyword>
<abstract>
<t>This document describes a common output format of Passive DNS Servers which clients can query. The output format description includes also in addition a common semantic for each Passive DNS system. By having multiple Passive DNS Systems adhere to the same output format for queries, users of multiple Passive DNS servers will be able to combine result sets easily.</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>Passive DNS is a technique described by Florian Weimer in 2005 in <xref target="WEIMERPDNS">Passive DNS replication, F Weimer - 17th Annual FIRST Conference on Computer Security</xref>. Since then multiple Passive DNS implementations were created and evolved over time. Users of these Passive DNS servers may query a server (often via <xref target="RFC3912">WHOIS</xref> or HTTP <xref target="REST">REST</xref>), parse the results and process them in other applications.</t>
<t>
There are multiple implementations of Passive DNS software. Users of passive DNS query each implementation and aggregate the results for their search. This document describes the output format of four Passive DNS Systems (<xref target="DNSDB"/>, <xref target="PDNSCERTAT"/>, <xref target="PDNSCIRCL"/> and <xref target="PDNSCOF"/>) which are in use today and which already share a nearly identical output format.
As the format and the meaning of output fields from each Passive DNS need to be consistent, we propose in this document a solution to commonly name each field along with their corresponding interpretation. The format follows a simple key-value structure in <xref target="RFC4627">JSON</xref> format.
The benefit of having a consistent Passive DNS output format is that multiple client implementations can query different servers without having to have a separate parser for each
individual server. <xref target="PDNSCLIENT">passivedns-client</xref> currently implements multiple parsers due to a lack of standardization.
The document does not describe the protocol (e.g. <xref target="RFC3912">WHOIS</xref>, HTTP <xref target="REST">REST</xref>) nor the query format used to query the Passive DNS. Neither does this document describe "pre-recursor" Passive DNS Systems. Both of these are separate topics and deserve their own RFC document.
</t>
<section title="Requirements Language">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in <xref
target="RFC2119">RFC 2119</xref>.</t>
</section>
</section>
<section title="Limitation">
<t> As a Passive DNS servers can include protection mechanisms for their operation, results might be different due to those protection measures. These mechanisms filter out DNS answers if they fail some criteria. The <xref target="BAILIWICK">bailiwick algorithm</xref> protects the Passive DNS Database from <xref target="CACHEPOISONING">cache poisoning attacks</xref>.
Another limitation that clients querying the database need to be aware of is that each query simply gets a snapshot-answer of the time of querying. Clients MUST NOT rely on consistent answers. Nor must they assume that answers must be identical across multiple Passive DNS Servers.
</t>
</section>
<section title="Common Output Format">
<section title="Overview">
<t>The formatting of the answer follows the <xref target="RFC4627">JSON</xref> format. In fact, it is a subset of the full JSON language. Notable differences are the modified definition of whitespace ("ws"). The order of the fields is not significant for the same resource type. </t>
<t>The intent of this output format is to be easily parsable by scripts. Each JSON object is expressed on a single line to be processed by the client line-by-line. Every implementation MUST support the JSON output format.</t> <!-- note: it is "parsable" if you want to be really nit-picking. See: https://en.wiktionary.org/wiki/parsable -->
<t><xref target="app-additional">Examples of JSON</xref> output are in the appendix.</t>
</section>
<section title="ABNF grammar">
<figure><preamble>Formal grammar as defined in <xref target="RFC2234">ABNF</xref></preamble><artwork><![CDATA[
answer = entries
entries = * ( entry CR)
entry = "{" keyvallist "}"
keyvallist = [ member *( value-separator member ) ]
member = qm field qm name-separator value
name-separator = ws %x3A ws ; a ":" colon
value = value ; as defined in the JSON RFC
value-separator = ws %x2C ws ; , comma. As defined in JSON
field = "rrname" | "rrtype" | "rdata" | "time_first" |
"time_last" | "count" | "bailiwick" | "sensor_id" |
"zone_time_first" | "zone_time_last" | futureField
futureField = string
CR = %x0D
qm = %x22 ; " a quotation mark
ws = *(
%x20 | ; Space
%x09 ; Horizontal tab
)
]]></artwork></figure>
<t>Note that value is defined in <xref target="RFC4627">JSON</xref> and has the exact same specification as there. The same goes for the definition of string.</t>
</section>
<section title="Mandatory Fields">
<t>Implementation MUST support all the mandatory fields.</t>
<t>Uniqueness property: the tuple (rrname,rrtype,rdata) will always be unique within one answer per server. While rrname and rrtype are always individual JSON primitive types (strings, numbers, booleans or null), rdata MAY return multiple resource records or a single record. When multiple resource records are returned, rdata MUST be a JSON array. In the case of a single resource record is returned, rdata MUST be a JSON string.</t>
<section title="rrname">
<t>This field returns the name of the queried resource.</t>
</section>
<section title="rrtype">
<t>This field returns the resource record type as seen by the passive DNS. The key is rrtype and the value is in the interpreted record type represented as a <xref target="RFC4627">JSON</xref> string. If the value cannot be interpreted the decimal value is returned following the principle of transparency as described in <xref target="RFC3597">RFC 3597</xref>. Then the decimal value is represented as a <xref target="RFC4627">JSON</xref> number.
The resource record type can be any values as described by IANA in the DNS parameters document in the section 'Resource Record (RR) TYPEs' (http://www.iana.org/assignments/dns-parameters).
Currently known and supported textual descriptions of rrtypes are: A, AAAA, CNAME, PTR, SOA, TXT, DNAME, NS, SRV, RP, NAPTR, HINFO, A6.
A client MUST be able to understand these textual rrtype values represented as a <xref target="RFC4627">JSON</xref> string. In addition, a client MUST be able to handle a decimal value (as mentioned above) as answer represented as a <xref target="RFC4627">JSON</xref> number.
</t>
</section>
<section title="rdata">
<t>This field returns the resource records of the queried resource. When multiple resource records are returned, rdata MUST be a JSON array. In the case of a single resource record is returned, rdata MUST be a JSON string. Each resource record is represented as a <xref target="RFC4627">JSON</xref> string. Each resource record MUST be escaped as defined in section 2.6 of <xref target="RFC4627">RFC4627</xref>. Depending on the rrtype, this can be an IPv4 or IPv6 address, a domain name (as in the case of CNAMEs), an SPF record, etc. A client MUST be able to interpret any value which is legal as the right hand side in a DNS master file <xref target="RFC1035">RFC 1035</xref> and <xref target="RFC1034">RFC 1034</xref>. If the rdata came from an unknown DNS resource records, the server must follow the transparency principle as described in <xref target="RFC3597">RFC 3597</xref>.</t>
</section>
<section title="time_first">
<t>This field returns the first time that the record / unique tuple (rrname, rrtype, rdata) has been seen by the passive DNS. The date is expressed in seconds (decimal) since 1st of January 1970 (Unix timestamp). The time zone MUST be UTC. This field is represented as a <xref target="RFC4627">JSON</xref> number.</t>
</section>
<section title="time_last">
<t>This field returns the last time that the unique tuple (rrname, rrtype, rdata) record has been seen by the passive DNS. The date is expressed in seconds (decimal) since 1st of January 1970 (Unix timestamp). The time zone MUST be UTC. This field is represented as a <xref target="RFC4627">JSON</xref> number.</t>
</section>
</section>
<section title="Optional Fields">
<t>Implementations SHOULD support one or more fields.</t>
<section title="count">
<t>Specifies how many authoritative DNS answers were received at the Passive DNS Server's collectors with exactly the given set of values as answers (i.e. same data in the answer set - compare with the uniqueness property in "Mandatory Fields"). The number of requests is expressed as a decimal value. This field is represented as a <xref target="RFC4627">JSON</xref> number.</t>
</section>
<section title="bailiwick">
<t>The bailiwick is the best estimate of the apex of the zone where this data is authoritative.</t>
</section>
</section>
<section title="Additional Fields">
<t>Implementations MAY support the following fields:</t>
<section title="sensor_id">
<t>This field returns the sensor information where the record was seen. It is represented as a <xref target="RFC4627">JSON</xref> string.</t>
</section>
<section title="zone_time_first">
<t>This field returns the first time that the unique tuple (rrname, rrtype, rdata) record has been seen via master file import. The date is expressed in seconds (decimal) since 1st of January 1970 (Unix timestamp). The time zone MUST be UTC. This field is represented as a <xref target="RFC4627">JSON</xref> number.</t>
</section>
<section title="zone_time_last">
<t>This field returns the last time that the unique tuple (rrname, rrtype, rdata) record has been seen via master file import. The date is expressed in seconds (decimal) since 1st of January 1970 (Unix timestamp). The time zone MUST be UTC. This field is represented as a <xref target="RFC4627">JSON</xref> number.</t>
</section>
<section title="origin">
<t>Specifies the resource origin of the Passive DNS response. This field is represented as a <xref target="RFC3986">Uniform Resource Identifier</xref> (URI).
</t>
</section>
</section>
<section title="Additional Fields Registry">
<t>In accordance with <xref target="RFC6648"/>, designers of new passive DNS applications that would need additional fields can request and register new field name at https://github.com/adulau/pdns-qof/wiki/Additional-Fields.</t>
</section>
</section>
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<?rfc needLines="8" ?>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>Thanks to the Passive DNS developers who contributed to the document.</t>
</section>
<!-- Possibly a 'Contributors' section ... -->
<section anchor="IANA" title="IANA Considerations">
<t>This memo includes no request to IANA.</t>
</section>
<section anchor="Privacy" title="Privacy Considerations">
<t>Passive DNS Servers capture DNS answers from multiple collecting points ("sensors") which are located on the Internet-facing side of DNS recursors ("post-recursor passive DNS"). In this process, they intentionally omit the source IP, source port, destination IP and destination port from the captured packets. Since the data is captured "post-recursor", the timing information (who queries what) is lost, since the recursor will cache the results. Furthermore, since multiple sensors feed into a passive DNS server, the resulting data gets mixed together, reducing the likelihood that Passive DNS Servers are able to find out much about the actual person querying the DNS records nor who actually sent the query. In this sense, passive DNS Servers are similar to keeping an archive of all previous phone books - if public DNS records can be compared to phone numbers - as they often are.
Nevertheless, the authors strongly encourage Passive DNS implementors to take special care of privacy issues. bortzmeyer-dnsop-dns-privacy is an excellent starting point for this.
Finally, the overall recommendations in <xref target="RFC6973">RFC6973</xref> should be taken into consideration when designing any application which uses Passive DNS data.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>In some cases, Passive DNS output might contain confidential information and its access might be restricted. When a user is querying multiple Passive DNS and aggregating the data, the sensitivity of the data must be considered.</t>
</section>
</middle>
<!-- *****BACK MATTER ***** -->
<back>
<!-- References split into informative and normative -->
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2. simply use a PI "less than character"?rfc include="reference.RFC.2119.xml"?> here
(for I-Ds: include="reference.I-D.narten-iana-considerations-rfc2434bis.xml")
Both are cited textually in the same manner: by using xref elements.
If you use the PI option, xml2rfc will, by default, try to find included files in the same
directory as the including file. You can also define the XML_LIBRARY environment variable
with a value containing a set of directories to search. These can be either in the local
filing system or remote ones accessed by http (http://domain/dir/... ).-->
<references title="Normative References">
<!--?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml"?-->
&RFC2119;
&RFC1035;
&RFC1034;
&RFC3912;
&RFC4627;
&RFC5001;
&RFC3597;
&RFC6648;
&RFC2234;
&RFC6973;
&RFC3986;
</references>
<references>
<reference anchor="WEIMERPDNS" target="http://www.enyo.de/fw/software/dnslogger/first2005-paper.pdf">
<front>
<title>Passive DNS Replication</title>
<author fullname="Florian Weimer"/>
<date year="2005"/>
</front>
</reference>
<reference anchor="CACHEPOISONING" target="http://kurser.lobner.dk/dDist/DMK_BO2K8.pdf">
<front>
<title>Black ops 2008: It&#8217;s the end of the cache as we know it.</title>
<author fullname="Dan Kaminsky"/>
<date year="2008"/>
</front>
</reference>
<reference anchor="BAILIWICK" target="https://archive.farsightsecurity.com/Passive_DNS/passive_dns_hardening_handout.pdf">
<front>
<title>Passive DNS Hardening</title>
<author fullname="Robert Edmonds"/>
<date year="2010"/>
</front>
</reference>
<reference anchor="PDNSCLIENT" target="https://github.com/chrislee35/passivedns-client">
<front>
<title>Queries 5 major Passive DNS databases: BFK, CERTEE, DNSParse, ISC, and VirusTotal.</title>
<author fullname="Chris Lee"/>
<date year="2013"/>
</front>
</reference>
<reference anchor="REST" target="http://www.ics.uci.edu/~fielding/pubs/dissertation/rest_arch_style.htm">
<front>
<title>Representational State Transfer (REST)</title>
<author fullname="Roy Thomas Fielding"/>
<date year="2000"/>
</front>
</reference>
<reference anchor="DNSDB" target="https://api.dnsdb.info/">
<front>
<title>DNSDB API</title>
<author fullname="Farsight Security"/>
<date year="2013"/>
</front>
</reference>
<reference anchor="PDNSCERTAT" target="http://www.centr.org/system/files/agenda/attachment/rd4-papst-passive_dns.pdf">
<front>
<title>pDNS presentation at 4th Centr R&amp;D workshop Frankfurt Jun 5th 2012</title>
<author fullname="CERT.at"/>
<date year="2012"/>
</front>
</reference>
<reference anchor="PDNSCIRCL" target="https://www.circl.lu/services/passive-dns/">
<front>
<title>CIRCL Passive DNS</title>
<author fullname="CIRCL -Computer Incident Response Center Luxembourg"/>
<date year="2012"/>
</front>
</reference>
<reference anchor="PDNSCOF" target="https://github.com/adulau/pdns-qof-server/">
<front>
<title>Passive DNS server interface using the common output format</title>
<author fullname="Alexandre Dulaunoy"/>
<date year="2013"/>
</front>
</reference>
</references>
<references title="Informative References">
<!-- Here we use entities that we defined at the beginning. -->
&RFC3552;
&I-D.narten-iana-considerations-rfc2434bis;
<!-- &I-D.draft-bortzmeyer-dnsop-dns-privacy; -->
</references>
<section anchor="app-additional" title="Examples">
<t>The JSON output are represented on multiple lines for readability but each JSON object should on a single line.</t>
<t>If you query a passive DNS for the rrname www.ietf.org, the passive dns common output format can be:</t>
<figure><artwork>
<![CDATA[
{"count": 102, "time_first": 1298412391, "rrtype": "AAAA",
"rrname": "www.ietf.org", "rdata": "2001:1890:1112:1::20",
"time_last": 1302506851}
{"count": 59, "time_first": 1384865833, "rrtype": "A",
"rrname": "www.ietf.org", "rdata": "4.31.198.44",
"time_last": 1389022219}
]]>
</artwork></figure>
<t>If you query a passive DNS for the rrname ietf.org, the passive dns common output format can be:</t>
<figure><artwork>
<![CDATA[
{"count": 109877, "time_first": 1298398002, "rrtype": "NS",
"rrname": "ietf.org", "rdata": "ns1.yyz1.afilias-nst.info",
"time_last": 1389095375}
{"count": 4, "time_first": 1298495035, "rrtype": "A",
"rrname": "ietf.org", "rdata": "64.170.98.32",
"time_last": 1298495035}
{"count": 9, "time_first": 1317037550, "rrtype": "AAAA",
"rrname": "ietf.org", "rdata": "2001:1890:123a::1:1e",
"time_last": 1330209752}
]]>
</artwork></figure>
<t>Please note that in the examples above, any backslashes "\" can be ignored and are an artefact of the tools which produced this document.</t>
</section>
</back>
</rfc>