Resource Records (RR) are fundamental data elements in the Domain Name System (DNS). They specify DNS dataset types and are used to provide responses to queries against the DNS system, mapping domain names to various types of data. Each record has a type, an expiration time (TTL), a name, and data. Here are some of the most common types of DNS Resource Records:
A (Address Record): Maps a domain name to an IPv4 address.
- Example:
example.com A 192.0.2.1
AAAA (Quad-A Record): Maps a domain name to an IPv6 address.
- Example:
example.com AAAA 2001:0db8::2:1
CNAME (Canonical Name Record): Points one domain name (an alias) to another domain name (the canonical name).
- Example:
www.example.com CNAME example.com
MX (Mail Exchange Record): Specifies a mail server responsible for accepting email messages on behalf of a domain name.
- Example:
example.com MX 10 mail.example.com
NS (Name Server Record): Specifies authoritative name servers for the domain.
- Example:
example.com NS ns1.exampledns.com
PTR (Pointer Record): Maps an IP address to a domain name, primarily used for reverse DNS lookups.
- Example:
1.2.0.192.in-addr.arpa PTR example.com
SRV (Service Record): Provides information about available services, like SIP or XMPP.
- Example:
_sip._tcp.example.com SRV 10 50 5060 sipserver.example.com
TXT (Text Record): Often used to hold descriptive text, but also often for machine-readable data such as SPF data to help prevent email spam.
- Example:
example.com TXT "v=spf1 +a +mx -all"
SOA (Start of Authority Record): Contains administrative information about the zone and is the record type that marks the start of a DNS zone.
- Example: Contains authoritative server, email of an admin, and other metadata about the domain.
CAA (Certification Authority Authorization): Specifies which certificate authorities are allowed to issue certificates for a domain.
- Example:
example.com CAA 0 issue "letsencrypt.org"
There are many other types of resource records, but these are among the most common. The data in resource records is used by DNS servers to respond to client queries, directing them to the correct locations or providing them with the necessary information to connect to services associated with domain names.