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Domain Name System Operations A. Dulaunoy
Internet-Draft CIRCL
Intended status: Informational A. Kaplan
Expires: 29 October 2024
P. Vixie
H. Stern
Farsight Security, Inc.
W. Kumari
Google
27 April 2024
Passive DNS - Common Output Format
draft-dulaunoy-dnsop-passive-dns-cof-11
Abstract
This document describes a common output format of Passive DNS Servers
that clients can query. The output format description also includes
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 https://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 29 October 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Limitation . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Common Output Format . . . . . . . . . . . . . . . . . . . . 4
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. ABNF grammar . . . . . . . . . . . . . . . . . . . . . . 4
3.3. Mandatory Fields . . . . . . . . . . . . . . . . . . . . 5
3.3.1. rrname . . . . . . . . . . . . . . . . . . . . . . . 5
3.3.2. rrtype . . . . . . . . . . . . . . . . . . . . . . . 5
3.3.3. rdata . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3.4. time_first . . . . . . . . . . . . . . . . . . . . . 6
3.3.5. time_last . . . . . . . . . . . . . . . . . . . . . . 6
3.4. Optional Fields . . . . . . . . . . . . . . . . . . . . . 6
3.4.1. count . . . . . . . . . . . . . . . . . . . . . . . . 6
3.4.2. bailiwick . . . . . . . . . . . . . . . . . . . . . . 7
3.5. Additional Fields . . . . . . . . . . . . . . . . . . . . 7
3.5.1. sensor_id . . . . . . . . . . . . . . . . . . . . . . 7
3.5.2. zone_time_first . . . . . . . . . . . . . . . . . . . 7
3.5.3. zone_time_last . . . . . . . . . . . . . . . . . . . 7
3.5.4. origin . . . . . . . . . . . . . . . . . . . . . . . 7
3.5.5. time_first_ms . . . . . . . . . . . . . . . . . . . . 7
3.5.6. time_last_ms . . . . . . . . . . . . . . . . . . . . 8
3.6. Additional Fields Registry . . . . . . . . . . . . . . . 8
3.7. Additional notes . . . . . . . . . . . . . . . . . . . . 8
3.8. Suggested MIME Types . . . . . . . . . . . . . . . . . . 8
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. References . . . . . . . . . . . . . . . . . . . . . . . 10
8.3. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
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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 have evolved over time. Users of
these Passive DNS servers may query a server (often via WHOIS
[RFC3912] or 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], [DNSDBQ] , [PDNSCERTAT], [PDNSCIRCL]
and [PDNSCOF]) that are in use today and that already share a nearly
identical output format. As the format and the meaning of output
fields from each Passive DNS need to be consistent, this document
proposes a solution to commonly name each field along with its
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. Each of these are separate topics and deserve
their own RFC documents. This document describes the current best
practices implemented in various Passive DNS server implementations.
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 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-in-time answer at the time of
querying. Clients MUST NOT rely on existing answers from different
Passive DNS database. Nor should they assume that answers will be
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identical across multiple Passive DNS Servers.
3. Common Output Format
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 newline )
entry = ws "{" ws keyvallist ws "}" ws
keyvallist = [ member *( value-separator member ) ]
member = field name-separator value
name-separator = ws %x3A ws ; : colon
value-separator = ws %x2C ws ; , comma
field = field-name | futureField
field-name = "rrname" | "rrtype" | "rdata" | "time_first" |
"time_last" | "count" | "bailiwick" | "sensor_id" |
"zone_time_first" | "zone_time_last" | "origin" |
"time_first_ms" | "time_last_ms"
futureField = string
newline = [ CR ] LF
CR = %x0D ; Carrige return
LF = %x0A ; Line feed or New line
qm = %x22 ; " Quotation mark
ws = *(
%x20 | ; Space
%x09 ; Horizontal tab
)
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Note that value is defined in JSON [RFC4627] and has the same
specification as there. The same goes for the definition of string.
Note the changed definition of ws does not include CR or LF as those
are NOT allowed in NDJSON, and thus the definition here MUST be used
for other ABNF defitions in JSON [RFC4627] .
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
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 or a JSON array containing one JSON string.
Senders SHOULD send an array for rdata, but receivers MUST be able to
accept a single-string result for rdata.
3.3.1. rrname
This field returns the name of the queried resource. Represented as
a JSON [RFC4627] string.
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). Supported textual
descriptions of rrtypes include: A, AAAA, CNAME, etc. 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) answer represented as a JSON
[RFC4627] number.
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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 containing JSON strings. In the case of a single resource
record being returned, rdata MUST be a JSON string or a JSON array
containing one 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
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.
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3.4.2. bailiwick
The bailiwick is the best estimate of the apex of the zone where this
data is authoritative. This field is represented as a JSON [RFC4627]
string.
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.
If the data originate from sensors or probes which are part of a
publicly-known gathering or measurement system (e.g. RIPE Atlas), a
JSON [RFC4627] string SHOULD be prefixed.
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.
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)
in the form of a JSON [RFC4627] string.
3.5.5. time_first_ms
Same meaning as the field "time_first", with the only difference,
that the resolution is in milliseconds since 1st of January 1970
(UTC).
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3.5.6. time_last_ms
Same meaning as the field "time_last", with the only difference, that
the resolution is in milliseconds since 1st of January 1970 (UTC).
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.
3.7. Additional notes
An implementer of a passive DNS Server MAY chose to either return
time_first and time_last OR return zone_time_first and
zone_time_last. In pseudocode: (time_first AND time_last) OR
(zone_time_first AND zone_time_last). In this case,
zone_time_{first,last} replace the time_{first,last} fields.
However, this is not encouraged since it might be confusing for
parsers who will expect the mandatory fields time_{first,last}. See:
[github_issue_17]
3.8. Suggested MIME Types
An implementer of a passive DNS Server SHOULD serve a document in
this Common Output Format with a MIME header of "application/
x-ndjson".
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 collection
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
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Servers are able to find out much about the actual person querying
the DNS records. 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 taken into
consideration when designing any application which uses Passive DNS
data.
In the scope of the General Data Protection Regulation (GDPR -
Directive 95/46/EC), operators of Passive DNS Server needs to ensure
the legal ground and lawfulness of its operation.
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,
<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>.
[RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, DOI 10.17487/RFC2234,
November 1997, <https://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, <https://www.rfc-editor.org/info/rfc3597>.
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[RFC3912] Daigle, L., "WHOIS Protocol Specification", RFC 3912,
DOI 10.17487/RFC3912, September 2004,
<https://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,
<https://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,
<https://www.rfc-editor.org/info/rfc4627>.
[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,
<https://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,
<https://www.rfc-editor.org/info/rfc6973>.
8.2. References
[BAILIWICK]
Edmonds, R., "Passive DNS Hardening", 2010,
<https://archive.farsightsecurity.com/Passive_DNS/
passive_dns_hardening_handout.pdf>.
[CACHEPOISONING]
Kaminsky, D., "Black ops 2008: It's the end of the cache
as we know it.", 2008,
<http://kurser.lobner.dk/dDist/DMK_BO2K8.pdf>.
[DNSDB] Security, F., "DNSDB API", 2013,
<https://api.dnsdb.info/>.
[DNSDBQ] Vixie, P., "DNSDB API Client, C Version", 2018,
<https://github.com/dnsdb/dnsdbq>.
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[github_issue_17]
et.al, P. V. W. A. K., "Discussion on the existing
implementations of returning either zone_time{first,last}
OR time_{first,last}", 2020,
<https://github.com/adulau/pdns-qof/issues/17>.
[PDNSCERTAT]
CERT.at, "pDNS presentation at 4th Centr R&D workshop
Frankfurt Jun 5th 2012", 2012,
<http://www.centr.org/system/files/agenda/attachment/d4-
papst-passive_dns.pdf>.
[PDNSCIRCL]
Luxembourg, C. -. I. R. C., "CIRCL Passive DNS", 2012,
<https://www.circl.lu/services/passive-dns/>.
[PDNSCLIENT]
Lee, C., "Queries 5 major Passive DNS databases: BFK,
CERTEE, DNSParse, ISC, and VirusTotal.", 2013,
<https://github.com/chrislee35/passivedns-client>.
[PDNSCOF] Dulaunoy, D. P. A., "Passive DNS server interface using
the common output format", 2019,
<https://github.com/D4-project/analyzer-d4-passivedns/>.
[REST] Fielding, R. T., "Representational State Transfer (REST)",
2000, <http://www.ics.uci.edu/~fielding/pubs/dissertation/
rest_arch_style.htm>.
[WEIMERPDNS]
Weimer, F., "Passive DNS Replication", 2005,
<http://www.enyo.de/fw/software/dnslogger/
first2005-paper.pdf>.
8.3. Informative References
Appendix A. Examples
The JSON output are represented on multiple lines for readability but
each JSON object should be on a single line.
If you query a passive DNS for the rrname www.ietf.org, the passive
dns common output format can be:
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{"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:
{"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 the examples imply that a single query returns a
single set of JSON objects. For example, two queries were made; one
query returned a set of two JSON objects and the other query returned
a set of three JSON objects. This specification requires each JSON
object individually MUST conform to the common output format, but
this specification does not require that a query will return a set of
JSON objects.
Please note that in the examples above, any backslashes "\" can be
ignored and are an artifact of the tools which produced this
document.
Authors' Addresses
Alexandre Dulaunoy
CIRCL
122, rue Adolphe Fischer
L-1521 Luxembourg
Luxembourg
Phone: (+352) 247 88444
Email: alexandre.dulaunoy@circl.lu
URI: http://www.circl.lu/
L. Aaron Kaplan
A-1170 Vienna
Austria
Email: aaron@lo-res.org
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Paul Vixie
Farsight Security, Inc.
11400 La Honda Road
Woodside, California 94062
United States of America
Email: paul@redbarn.org
URI: https://www.farsightsecurity.com/
Henry Stern
Farsight Security, Inc.
11400 La Honda Road
Woodside, California 94062
United States of America
Phone: +1 650 542-7836
Email: henry@stern.ca
URI: https://www.farsightsecurity.com/
Warren Kumari
Google
Email: warren@kumari.net
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