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The 'A' stands for 'address' and this is the most basic kind of DNS record: the IP address of a given domain is indicated. For instance, if you pull cloudflare.com DNS records, the A record currently returns an IP address of 18.104.22.168.
A records only hold IPv4 addresses. If a website has an IPv6 address, it will instead use an ‘AAAA’ record.
Here is an example of an A record:
example.com record type: value: TTL
@ A 192.0.2.1 14400
In this example, the '@' symbol indicates that this is a record for the root domain, and the TTL (time to live), specified in seconds, is the '14400' value. For A records, the default TTL is 14400 seconds. This implies that it takes 240 minutes (14400 seconds) to take effect if an A record gets changed.
There is only one A record for the vast majority of websites, although it is possible to have many. As part of a technique called round-robin load balancing, some higher profile websites may have several distinct A records, which can disperse request traffic to one of several IP addresses, each hosting identical content.
IP address lookups are the most popular use of A records: matching a domain name (like 'cloudflare.com') to an IPv4 address. This allows the computer of a user to connect to and load a website without memorising and typing in the actual IP address by the user. This is automatically carried out by the user's web browser by submitting a question to a DNS resolver.
For running a Domain Name System-based Blackhole List (DNSBL), DNS A records are also used. Mail servers may be supported by DNSBLs to recognise and block email messages from suspected spammers.