TXT record

A TXT record (short for text record) is a type of resource record in the Domain name systemically[1] (DNS) used to provide the ability to associate arbitrary text with a host or other name, such as human readable information about a server, network, data center, or other accounting information.[2]

Internet protocol suite
Application layer
Transport layer
Internet layer
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It is also often used in a more structured fashion to record small amounts of machine-readable data into the DNS.

Background

A domain may have multiple TXT records associated with it, provided the DNS server implementation supports this.[3] Each record can in turn have one or more character strings.[1] Traditionally these text fields were used for a variety of non-standardised uses, such as a full company or organisation name, or the address of a host.

In 1993 RFC 1464 proposed a simple approach to storing attributes and their values in these text fields. This is now used extensively in:

Format

As unstructured text, organisations can use the TXT string in any way they define, for example:

example.com.   IN   TXT   "This domain name is reserved for use in documentation"

RFC 1464 defines a structured format that can be used to define attributes and their values in a single record,[3] as in these examples:

host.widgets.com.   IN   TXT   "printer=lpr5"
sam.widgets.com.    IN   TXT   "favorite drink=orange juice"

In practice, services using TXT records often do not follow this RFC, but instead have their own specific format.[10][11]

Example usage

The character string from a TXT record used for SPF:

"v=spf1 ip4:192.0.2.0/24 ip4:198.51.100.123 ip6:2620:0:860::/46 a -all"

An example of use for DMARC: 

"v=DMARC1;p=none;sp=quarantine;pct=100;rua=mailto:dmarcreports@example.com;"

Use for site verification:

"google-site-verification=6P08Ow5E-8Q0m6vQ7FMAqAYIDprkVV8fUf_7hZ4Qvc8"

Use for custom email service:

_amazonses.example.com.   IN   TXT   "pmBGN/7MjnfhTKUZ06Enqq1PeGUaOkw8lGhcfwefcHU="
gollark: I know some people with "Apple Watches" and stuff, but they don't actually seem very useful.
gollark: (it's smart because it has a microcontroller in it, probably)
gollark: The best smartwatch is a Casio F-91W.
gollark: I checked, and MacOS also only has it as an option.
gollark: Theoretically you can also use this via setting up your own secure boot keys, if you trust the (closed-source, probably never really audited) UEFI implementation.

See also

References
  1. P. Mockapetris (November 1987). "TXT RDATA format". Domain names - implementation and specification. IETF. sec. 3.3.14. doi:10.17487/RFC1035. RFC 1035.
  2. Rich Rosenbaum (May 1993). RFC 1464 Using the Domain Name System To Store Arbitrary String Attributes. IETF. doi:10.17487/RFC1464. RFC 1464. Retrieved 2016-02-05.
  3. Rosenbaum, R. "Using the Domain Name System To Store Arbitrary String Attributes". Tools.ietf.org. Retrieved 14 October 2018.
  4. "Verify your site ownership". Retrieved 18 December 2018.
  5. "Domain Verification". Facebook. Retrieved 18 December 2018.
  6. Scott Kitterman (April 2014). "DNS Resource Records". Sender Policy Framework (SPF) for Authorizing Use of Domains in Email, Version 1. IETF. sec. 3.1. doi:10.17487/RFC7208. RFC 7208. Retrieved 2014-04-26.
  7. "About TXT records". Google Apps Administration. Retrieved 2014-08-17.
  8. S. Cheshire and M. Krochmal, Apple Inc. (February 2013). Multicast DNS. IETF. doi:10.17487/RFC6762. RFC 6762.
  9. S. Cheshire and M. Krochmal, Apple Inc. (February 2013). DNS-Based Service Discovery. IETF. doi:10.17487/RFC6763. RFC 6763.
  10. "DNS Record Verification". WebNots. Retrieved 21 December 2018.
  11. "Amazon SES Domain Verification TXT Records". Amazon. Retrieved 21 December 2018.
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