Definitions

mail exchange record

List of DNS record types

The Domain name system (DNS) implements a distributed, hierarchical, and redundant database for information associated with Internet domain names and addresses. This List of DNS record types provides an overview of types of database records (resource records) stored in the zone files of this system.

Code Number Defining RFC Description Function
A
1 RFC 1035 address record Returns a 32-bit IPv4 address, most commonly used to map hostnames to an IP address of the host.
AAAA
28 RFC 3596 IPv6 address record Returns a 128-bit IPv6 address, most commonly used to map hostnames to an IP address of the host.
AFSDB
18 RFC 1183 AFS database record Location of database servers of an AFS cell. This record is commonly used by AFS clients to contact AFS cells outside their local domain. A subtype of this record is used by the obsolete DCE/DFS file system.
AXFR 252 RFC 1035 Full Zone Transfer Transfer entire zone file from the master name server to secondary name servers.
CERT
37 RFC 4398 Certificate record Stores PKIX, SPKI, PGP, etc.
CNAME
5 RFC 1035 Canonical name record Alias of one name to another: the DNS lookup will continue by retrying the lookup with the new name. This helps when running multiple services (like an FTP and a webserver; each running on different ports) from a single IP address. Each service can then have its own entry in DNS (like ftp.example.com. and www.example.com.). Network administrators also use CNAMEs when running multiple HTTP servers on the same port, with different names, on the same physical host. This however requires host headers support for the two sites to both listen on the default port (port 80).
DHCID
49 RFC 4701 DHCP identifier Used in conjunction with the FQDN option to DHCP
DLV
32769 RFC 4431 DNSSEC Lookaside Validation record For publishing DNSSEC trust anchors outside of the DNS delegation chain
DNAME
39 RFC 2672 delegation name Unlike the CNAME record, which creates a single alias, a DNAME will delegate an entire portion of the DNS tree under a new name. Like the CNAME record, the DNS lookup will continue by retrying the lookup with the new name.
DNSKEY
48 RFC 3755 DNS Key record The key record used in DNSSEC
DS
43 RFC 3658 Delegation signer The record used to identify the DNSSEC signing key of a delegated zone
HIP 55 RFC 5205 Host Identity Protocol Method of separating the end-point identifier and locator roles of IP addresses.
IPSECKEY
45 RFC 4025 IPSEC Key Key record that can be used with IPSEC
IXFR 251 RFC 1995 Incremental Zone Transfer Transfer the changed parts of the zone file from the master name server to secondary name servers.
KEY
25 RFC 4034 Key record Used only for TKEY (RFC 2930). Before RFC 3755 was published, this was also used for DNSSEC, but DNSSEC now uses DNSKEY.
LOC 29 RFC 1876 Location record Specifies a geographical location associated with a domain name
MX 15 RFC 1035 mail exchange record Maps a domain name to a list of mail exchange servers for that domain
NAPTR 35 RFC 3403 Naming Authority Pointer Newer type of DNS record that supports regular expression based rewriting
NS
2 RFC 1035 name server record Delegates a DNS zone to use the given authoritative name servers
NSEC
47 RFC 3755 Next-Secure record Part of DNSSEC—used to prove a name does not exist
NSEC record version 3
An extension to DNSSEC that allows proof of nonexistence for a name without permitting zonewalking
NSEC3PARAM
51 RFC 5155 NSEC3 parameters Parameter record for use with NSEC3
OPT
41 RFC 2671 Option This is a "pseudo DNS record type" needed to support EDNS
PTR
12 RFC 1035 pointer record Pointer to a canonical name. Unlike a CNAME, DNS processing does NOT proceed, just the name is returned. The most common use is for implementing reverse DNS lookups by putting a PTR record for a hostname in the in-addr.arpa. domain that corresponds to an IP address. For example (at the time of writing), www.icann.net has the IP address 192.0.34.164, but a PTR record maps 164.34.0.192.in-addr.arpa to its canonical name, referrals.icann.org.
RRSIG
46 RFC 3755 DNSSEC signature Signature for a DNSSEC-secured record set
SIG
24 RFC 2535 Signature Signature record used in SIG(0) (RFC 2931). Until RFC 3755 was published, the SIG record was part of DNSSEC; now RRSIG is used for that.
SOA
6 RFC 1035 start of authority record Specifies authoritative information about a DNS zone, including the primary name server, the email of the domain administrator, the domain serial number, and several timers relating to refreshing the zone.
SPF
99 RFC 4408 SPF record Specified as part of the SPF protocol, as an alternative to storing SPF data in TXT records.
SRV 33 RFC 2782 Service locator Generalized service location record, used for newer protocols instead of creating protocol-specific records such as MX.
SSHFP
44 RFC 4255 SSH Public Key Fingerprint Resource record for publishing SSH public host key fingerprints in the DNS System, in order to aid in verifying the authenticity of the host.
TA
32768 None DNSSEC Trust Authorities Part of a deployment proposal for DNSSEC without a signed DNS root. See the IANA database and Weiler Spec] for details
TKEY 249 RFC 2930 Transaction Key Record that supports one set of security mechanisms for the DNS. Used between DNS resolvers and Name servers, in contrast to DNSSEC, which secures DNS records.
TSIG 250 RFC 2845 Transaction Signature Record that supports one set of security mechanisms for DNS. Used between DNS resolvers and Name servers, in contrast to DNSSEC, which secures DNS records.
TXT
16 RFC 1035 Text record Originally for arbitrary human-readable text in a DNS record. Since the early 1990s, however, this record more often carries machine-readable data, such as specified by RFC 1464, opportunistic encryption, Sender Policy Framework and DomainKeys.

Other types

Other types of records simply provide some types of information (for example, an HINFO record gives a description of the type of computer/OS a host uses), or others return data used in experimental features.

The "type" field is also used in the protocol for various operations; type 255 is a request for "all cached records of all types", 252 (AXFR) is a request for transfer of a zone, TKEY and TSIG are used for transaction signing (different from record signing).

Obsolete record types

Progress has obsoleted some of the originally-defined record-types. Of the records listed at IANA, some have limited use, for various reasons. Some are marked obsolete in the list, some are for very obscure services, some are for older versions of services, and some have special notes saying they're "not right".

  • Obsoleted by RFC 973: MD(3), MF (4), MAILA (254)
  • Records to publish mailing list subscriber lists in the DNS: MB(7), MG(8), MR(9), MINFO(14), MAILB (253). The intent, as specified by RFC 883, was for MB to replace the SMTP VRFY command, MG to replace the SMTP EXPN command, and MR to replace the "551 User Not Local" SMTP error. Later, RFC 2505 recommends that both the VRFY and EXPN commands be disabled.
  • Declared "not to be relied upon" by RFC 1123: WKS(11)
  • Mistakes: NB(32), NBSTAT(33) (from RFC 1002); the numbers are now assigned to NIMLOC and SRV.
  • Obsoleted by RFC 1035: NULL(10) (RFC 883 defined "completion queries", opcode 2, which used this record. RFC 1035 reserved this opcode.)
  • Defined as part of early IPv6 but downgraded to experimental by RFC 3363: A6(38)
  • Obsoleted by DNSSEC updates (RFC 3755): NXT(30). The domain of applicability for KEY and SIG was also limited to not include DNSSEC use.
  • Part of the first version of DNSSEC (RFC 2230/RFC 2065), now obsolete: KX(36)
  • Not in current use by any notable application: HINFO(13), RP(17), X25(19), ISDN(20), RT(21), NSAP(22), NSAP-PTR(23), PX(26), EID(31), NIMLOC(32), ATMA(34), APL(42)
  • Defined by the Kitchen Sink internet draft, but never made it to RFC status: SINK(40)
  • A more limited early version of the LOC record: GPOS(27)
  • IANA reserved, no RFC documented them and support was removed from BIND in the early 90s: UINFO(100), UID(101), GID(102), UNSPEC(103)

Further reading

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References

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