What is DNS?
The Domain Name System (DNS) is the hierarchical and decentralized naming system used to identify computers, services, and other resources reachable through the Internet or other Internet Protocol (IP) networks. The resource records contained in the DNS associate domain names with other forms of information. These are most commonly used to map human-friendly domain names to the numerical IP addresses computers need to locate services and devices using the underlying network protocols, but have been extended over time to perform many other functions as well. The Domain Name System has been an essential component of the functionality of the Internet since 1985.
| Record type | Description and extra columns |
|---|---|
| A |
Returns a 32-bit IPv4 address, most commonly used to map hostnames to an IP address of the host, but it is also used for DNSBLs, storing subnet masks in RFC 1101, etc. ip: An IPv4 addresses in dotted decimal notation. |
| AAAA | ipv6: IPv6 address |
| A6 | masklen: Length (in bits) to inherit from the target
specified by chain. ipv6: Address for this specific record to merge with chain. chain: Parent record to merge with ipv6 data. |
| MX |
A mail exchanger record (MX record) specifies the mail server responsible for accepting email messages on behalf of a domain name. It is a resource record in the Domain Name System (DNS). It is possible to configure several MX records, typically pointing to an array of mail servers for load balancing and redundancy. pri: Priority of mail exchanger. Lower numbers indicate greater priority. target: FQDN of the mail exchanger. |
| CNAME | target: FQDN of location in DNS namespace to which the record is aliased. |
| NS | target: FQDN of the name server which is authoritative for this hostname. |
| PTR | target: Location within the DNS namespace to which this record points. |
| TXT | txt: Arbitrary string data associated with this record. |
| HINFO | cpu: IANA number designating the CPU of the machine
referenced by this record. os: IANA number designating the Operating System on the machine referenced by this record. |
| CAA | flags: A one-byte bitfield; currently only bit 0 is defined,
meaning 'critical'; other bits are reserved and should be ignored. tag: The CAA tag name (alphanumeric ASCII string). value: The CAA tag value (binary string, may use subformats). |
| SOA | mname: FQDN of the machine from which the resource
records originated. rname: Email address of the administrative contact for this domain. serial: Serial # of this revision of the requested domain. refresh: Refresh interval (seconds) secondary name servers should use when updating remote copies of this domain. retry: Length of time (seconds) to wait after a failed refresh before making a second attempt. expire: Maximum length of time (seconds) a secondary DNS server should retain remote copies of the zone data without a successful refresh before discarding. minimum-ttl: Minimum length of time (seconds) a client can continue to use a DNS resolution before it should request a new resolution from the server. Can be overridden by individual resource records. |
| SRV | A Service record (SRV record) is a specification of data in the Domain Name System defining the location, i.e., the hostname and port number, of servers for specified services. It is defined in RFC 2782, and its type code is 33. Some Internet protocols such as the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP) often require SRV support by network elements. |
| NAPTR | A Name Authority Pointer (NAPTR) is a type of resource record in the Domain Name System of the Internet. NAPTR records are most commonly used for applications in Internet telephony, for example, in the mapping of servers and user addresses in the Session Initiation Protocol (SIP) |