A Record A Record


What is an A record?


DNS records are used to control the location of a resource on the Internet. A Records are the most basic type of DNS record and are used to point a domain or subdomain to an IP address. The ‘A’ stands for ‘address’. For example, if you query the A records of google.com, it currently returns an IP address of 172.217.3.174. 172.217.3.174 is the IP address of the hosting server for Google's website.

Most of the websites only have one A record, but some have more than one. Some websites host identical contents on several hosting servers with different IP addresses in different geolocations and point their domain name to the IP addresses of those hosting servers. By using a technique called round robin, they can forward users to one of hosting servers to balance the load.

A record format


A typical A record looks like the following in standard BIND format: 

$ORIGIN example.com.
@ 3600 IN A 223.89.20.79 
* 3600 IN A 223.89.20.79 
ftp 86400 IN A 201.52.12.36
An anatomy of the A Record @ 3600 IN A 223.89.20.79 looks like the below:
Host Label TTL Record Class Record Type Record Data
example.com. 3600 IN A 223.89.20.79
Host Label
The host label defines the hostname of a record and whether the hostname will be appended to the label. Fully qualified hostnames terminated by a period will not append the origin.

TTL
The time-to-live in seconds. This is the amount of time the record is allowed to be cached by an outside DNS server.

Record Class
Mainly 3 classes of DNS records exist:
  • IN (Internet) – default and generally what internet uses.
  • CH (Chaosnet) – used for querying DNS server versions.
  • HS (Hesiod) – uses DNS functionality to provide access to databases of information that change infrequently.

Record Type
The record format is defined using this field. Common record types are A, AAAA, CNAME, CAA, TXT etc.

Record Data
The data within a DNS answer. For an A record, the record data contains an IP address. Different record types will contain different types of record data.

How to add an A record?


For instructions on how to add an A record with us, you may refer to the tutorial here.

A record glossary


A Record
Maps hostnames to an IP address. For example, the A record for google.com points the IP address 172.217.3.174.

IP Address
IP address stands for Internet Protocol Address and it is a numerical address assigned to computers and servers on the Internet. There currently are two popular versions of Internet Protocol: IPv4 and IPv6. An A record contains only IPv4 address information. AAAA records deal with IPv6 address information.

IPv4/IPv6 Address
There currently are two versions of Internet Protocol, IPv4 and IPv6. IPv4 addresses are usually represented in dot-decimal notation, consisting of four decimal numbers, each ranging from 0 to 255, separated by dots, 200.123.12.45 is an example of IPv4 address. As IPv4 has a limited capacity of IP addresses, the world has run out of unallocated IPv4 addresses. A new version of IP (IPv6), using 128 bits for the IP address, is deemed sufficient for the foreseeable future. An example of IPv6 is 2001:4670:ff28::1036.

IPv4 address exhaustion
IPv4 address exhaustion is the depletion of the pool of unallocated IPv4 addresses due to the limited number (4.3 billion) of IPv4 addresses. The exhaustion was foreseen since the 1980s and came to truth a few years ago. Currently, IPv4 and IPv6 coexist on the Internet.

BIND
Berkeley Internet Name Daemon - is the most commonly used DNS software on the Internet and Dynu observes BIND format.

DNS
The Domain Name System (DNS) is the phone book of the Internet. People access information online through easy-to-remember domain names. Computers communicate through Internet Protocol (IP) addresses. DNS translates domain names to IP addresses so browsers can load Internet resources.

DNS Caching
DNS caching is the amount of a time that a DNS server will retain existing DNS records before checking with the authoritative name servers for updates. The amount of time that records are cached is usually determined by the TTL set by the authoritative nameserver, but some ISPs may cache the records longer.

Authoritative Name Server
An authoritative Name Server is a nameserver (DNS Server) that holds the actual DNS records (A, AAAA, TXT, etc) for a particular domain/ address. Authoritative Name Servers need to be set up at the domain registrar and they only respond to DNS queries for the domain names that they host.

DNS Recursive Resolver
a DNS server that queries an authoritative nameserver to resolve a domain/ address.

Dynamic DNS
A method of mapping a static hostname to a dynamic IP address automatically. A computer software or router built-in software is needed to achieve this.
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