DNS Record Types

A — IPv4 address (We support)

The A or “address” DNS record type was created to hold IPv4 addresses. Translating names to addresses is one of the most fundamental uses of the DNS!

The A record type was introduced in the original DNS specifications (RFC 1034 and 1035) in 1987. Each type A record holds an IPv4 address. IPv6 did not yet exist in 1987 so all addresses were 32-bit IPv4 addresses. The AAAA DNS record type for IPv6 records would come later.

The DNS was created because the original system for mapping names to address, the “hosts” file, was quickly becoming unsustainable. The DNS would allow applications to map human-readable names into addresses in a massive globally distributed database. The A record type associates IPv4 addresses with DNS names.

Today, the DNS performs many other critical functions. But one of its most important jobs remains the mapping of names to addresses.

AAAA — IPv6 address (We support)

The AAAA DNS record type was created to hold IPv6 addresses. AAAA records, pronounced “quad A records” are similar to A records. They hold a 128-bit IPv6 address instead of a 32-bit IPv4 address.

IPv6 did not exist when the original DNS specifications (RFC 1034 and 1035) were written. Only a few years later, IPv6 was created to address the problem of IPv4 address space exhaustion. The AAAA record type was introduced in RFC 1886 in 1995. RFC 3596 is the current specification for AAAA records in the DNS.

AFSDB — AFS database location

APL — Address prefix list

AXFR — Authoritative zone transfer

CAA — Certification authority authorization (We support)

CDNSKEY — Child copy of a DNSKEY

CDS — Child copy of DS

CERT — Cryptographic certificate

CNAME — Canonical name (We support)

The CNAME or “canonical name” DNS record type is used to alias or redirect one DNS name to another DNS name.

This record type was introduced in the original DNS specifications (RFC 1034 and 1035) in 1987. CNAME records have not changed much since then, but CNAME remains a powerful and useful tool in any DNS toolbox.

CSYNC — Child-to-parent synchronization

DHCID — DHCP identifier

DLV — DNSSEC Look-Aside validation

DNAME — Delegation name

DNSKEY — Cryptographic key for DNSSEC

DS — Delegation signer (We support)

EUI48 — MAC address (EUI-48)

EUI64 — Mac address (EUI-64)

HINFO — Host information

HIP — Host identification protocol

HTTPS — HTTPS binding (We support)

IPSECKEY — Cryptographic key for IPsec

IXFR — Incremental zone transfer

KEY — Cryptographic key for DNSSEC (obsoleted by DNSKEY)

KX — Key exchange

LOC — Geographical location

MX — Mail exchange (We support)

The MX or “mail exchange” DNS record type is critical to the delivery of email via the Simple Mail Transfer Protocol (SMTP). MX records are used to specify a list of mail servers for a domain. If MX records are not created and maintained correctly, email for the domain will not be delivered reliably or perhaps at all.

The MX record type was introduced in the original DNS specifications (RFC 1034 and 1035) in 1987.

NAPTR — Naming authority pointer

NS — Name server (We support)

The NS or “name server” DNS record type is used to specify the authoritative name servers for a domain. It tells DNS resolvers which servers to contact when it's looking for DNS records for that domain name. This is what allows different organizations to own different domain names.

Like a number of other DNS record types, the original DNS specifications (RFC 1034 and 1035) introduced this record type in 1987. Along with the Start of Authority (SOA) record type, NS records are integral to the proper functioning of the DNS.

NSEC3 — Next secure (Version 3)

NSEC3PARAM — Parameter for NSEC3

NSEC — Next secure (obsoleted by NSEC3)

NXT — DNSSEC key (obsoleted by NSEC)

OPENPGPKEY — Public key for OpenPGP

OPT — EDNS option

PTR — Canonical name pointer (We support)

The PTR or "pointer" DNS record type maps an IP address to a domain name in the DNS. This is called a DNS reverse lookup.

Most DNS records types are used in "forward lookups". A DNS forward lookup maps a DNS name to an IP address or another piece of DNS data. PTR records do the opposite. A reverse lookup for a PTR record maps an IP address to a DNS name.

The PTR record type was introduced in the original DNS specifications (RFC 1034 and 1035) in 1987. Today, PTR records are essential for email delivery. They are used as a layer of security to prove that a mail server is trustworthy.

RP — Responsible person

RRSIG — Resource record signature for DNSSEC

SIG — Resource record signature for DNSSEC (obsoleted by RRSIG)

SMIMEA — S/MIME association

SOA — Start of authority

All DNS zones begin with a Start Of Authority (SOA) record. The SOA record states that authority for a zone is starting at a particular point in the global tree of DNS names.

For example, when creating a new DNS zone for shortestdomain.com then the process of zone creation would include the creation of a SOA record at shortestdomain.com.

Maintenance and creation of the SOA record is a task for the DNS server administrator of the zone. The webmaster for a domain would not generally need to add or change the SOA record.

The SOA record at shortestdomain.com indicates that a DNS zone begins at ohmcar.org and extends downwards in the DNS tree to encompass all the DNS names that are children of shortestdomain.com. The names www.shortestdomain.com and apps.backend.shortestdomain.com would be part of this zone, as would the name shortestdomain.com itself.

The SOA record does more than just indicate that a zone exists. It also gives some important information about the zone and controls negative caching for non-existent names within the zone.

SSHFP — Public key fingerprint for SSH (We support)

SVCB — Service binding (We support)

SPV — The Sender Policy Framework (We support)

SRV — Service locator (We support)

The SRV or "service locator" DNS record type enables service discovery in the DNS. SRV records allow services to be advertised on specific ports and used in an order controlled by the owner of the service. SRV also provides a load balancing feature.

The SRV record type was proposed in the late 1990s in RFC 2782. The SRV record addresses limitations in the DNS around advertising and consuming services. Not all application protocols support SRV, but many do.

TA — Trust authority for DNSSEC

TKEY — Transaction key

TLSA — Certificate association for TLS (We support)

TSIG — Transaction signature

TXT — Human-readable text (We support)

The TXT or “descriptive text” DNS record type was created to hold human-readable text. It now plays a critical role in the prevention of spam on the Internet.

The TXT record type was introduced in the original DNS specifications (RFC 1034 and 1035) in 1987. They were to be used for notes and text created by DNS administrators. There was originally no definitive purpose for TXT records. They were used for whatever information the DNS administrator thought was useful. This included contact information, the locations and owners of machines, humorous messages, and other administrivia.

TXT records were used this way until 2003. In 2003 efforts began to fight back against spam and other abuses of email. This led to the creation of SPF (Sender Policy Framework). SPF stores email authority information in TXT records. Other uses for the TXT record type have been added over the years.

URI — Uniform resource identifier

ZONEMD — Message digest for DNS zones