Network Working Group P. Hoffman Internet-Draft VPN Consortium Intended status: Experimental August 20, 2014 Expires: February 21, 2015 Representing DNS Messages in JSON draft-hoffman-dns-in-json-00 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 fully describes a standardized format for DNS message data in JSON. 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 February 21, 2015. Copyright Notice Copyright (c) 2014 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 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 Hoffman Expires February 21, 2015 [Page 1] Internet-Draft DNS in JSON August 2014 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 3. JSON Format for Streams of DNS Messages . . . . . . . . . . . 6 4. JSON Format for a Paired DNS Query and Response . . . . . . . 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 7 6. Local Format Policy . . . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 10.1. Normative References . . . . . . . . . . . . . . . . . . 9 10.2. Informative References . . . . . . . . . . . . . . . . . 9 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10 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 RFC 1035 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 stream of DNS queries or a stream of DNS responses, and how to describe a paired DNS query and response; these are useful for logging on a DNS server. Hoffman Expires February 21, 2015 [Page 2] Internet-Draft DNS in JSON August 2014 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 All values that are eight bits or shorter (even booleans) are represented by JSON integers. o Many values that can have non-ASCII data in them have names that end in "*" and are stored in base16 encoding (hex with uppercase letters) defined in [RFC4648]. o Some values will be very long and implementations might care about the size of the records on the wire. Values that are expected to be long (the entire record, some resource records such as those with cryptographic keys, and so on) have names that end in "!" and are stored in base64url encoding defined in [RFC4648]. o All names used in RFC 1035 are used in this format as-is. Names not defined in RFC 1035 use "camel case" with the first letter lowercase. o Because domain names that follow the host name rules are so common, there are additional members for domain names that are also host names and can be shown as unencoded strings. See [RFC1123] for the host name rules. 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 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. Hoffman Expires February 21, 2015 [Page 3] Internet-Draft DNS in JSON August 2014 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. Note that an object in this format can have zero or more of the members defined here; that is, no members are required. Also, an object can have members that are not defined in this document. 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 o ARCOUNT - Integer whose value is 0 to 65535 o QNAME* - The octets of the QNAME of the first Question section of the message o hostQNAME - The host name of the domain name in the QNAME, or an empty string if the QNAME is not a host name o QTYPE - Integer whose value is 0 to 65535, of the QTYPE of the first Question section of the message Hoffman Expires February 21, 2015 [Page 4] Internet-Draft DNS in JSON August 2014 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* - The octets of the NAME field of the resource record o hostNAME - The host name of the domain name in the NAME, or an empty string if the NAME is not a host name o expandedNAME* - The octets of the NAME field after RFC 1035 removing name compression o TYPE - Integer whose value is 0 to 65535 o CLASS - Integer whose value is 0 to 65535 o TTL - Integer whose value is 0 to 4294967295 o RDLENGTH - Integer whose value is 0 to 65535 o RDATA* - The octets of the RDATA field of the resource record o RDATA! - The octets of the RDATA field of the resource record The values of the NAME* and hostNAME and expandedNAME* members might all be the same, or could be different. A Question section can be expressed as a resource record. When doing so, the TTL, RDLENGTH, and RDATA* members make no sense. Hoffman Expires February 21, 2015 [Page 5] Internet-Draft DNS in JSON August 2014 2.3. The Message and Its Parts as Octets The following can be members of a message object. o messageOctets* - The octets of the message 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 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 o rrOctets! - The octets of a particular resource record 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] 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. 3. JSON Format for Streams of DNS Messages A strem of DNS messages is represented as an array of zero or more message objects. Hoffman Expires February 21, 2015 [Page 6] Internet-Draft DNS in JSON August 2014 4. 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. 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. { "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*": "076578616D706C6503636F6D00", "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 pity goes here" "dateSeconds": 1408504748.657783 "headerOctets*": "4CDE00000001000000000000" "hostQNAME": "example.com" "messageOctets*": "4CDE00000001000000000000076578616D706C6503636F6D0000010001" "messageOctets!": "TN4AAAABAAAAAAAAB2V4YW1wbGUDY29tAAABAAE=" "questionOctets*": "076578616D706C6503636F6D0000010001" "questionRRs": [ { "NAME*": "076578616D706C6503636F6D00", "TYPE": 1, "CLASS": 1, "hostNAME" : "example.com" } ] 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. Hoffman Expires February 21, 2015 [Page 7] Internet-Draft DNS in JSON August 2014 { "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*": "076578616D706C6503636F6D00", "QTYPE": 1, "QCLASS": 1 }, "responseRecord": { "ID": 32784, "QR": 1, "AA": 1, "RCODE": 0, "QDCOUNT": 1, "ANCOUNT": 1, "NSCOUNT": 1, "ARCOUNT": 0, "answerRRs": [ { "NAME*": "076578616D706C6503636F6D00", "TYPE": 1, "CLASS": 1, "TTL": 3600, "RDLENGTH": 4, "RDATA*": "16212C37" } ], "authorityRRs": [ { "NAME*": "026E73076578616D706C6503636F6D00", "TYPE": 1, "CLASS": 1, "TTL": 28800, "RDLENGTH": 4, "RDATA*": "A5E3F903", "hostNAME": "ns.example.com" } ] } } 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. 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 Hoffman Expires February 21, 2015 [Page 8] Internet-Draft DNS in JSON August 2014 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 discussions with Stephane Bortzmeyer. 10. References 10.1. Normative References [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987. [RFC1123] Braden, R., "Requirements for Internet Hosts - Application and Support", STD 3, RFC 1123, October 1989. [RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data Interchange Format", RFC 7159, March 2014. 10.2. Informative References [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. [RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, July 2002. [RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom Syndication Format", RFC 4287, December 2005. [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, October 2006. Hoffman Expires February 21, 2015 [Page 9] Internet-Draft DNS in JSON August 2014 Author's Address Paul Hoffman VPN Consortium Email: paul.hoffman@vpnc.org Hoffman Expires February 21, 2015 [Page 10]