The A (Address Record) is one of the most fundamental and commonly used record types in the Domain Name System (DNS). It serves the primary function of mapping a human-friendly domain name to an IP address, specifically an IPv4 address.
Characteristics of an A Record:
- Purpose: Maps a domain name to its corresponding IPv4 address.
- Format: The record typically consists of a domain name followed by its corresponding IP address.
- Example:
example.com. IN A 192.0.2.1
In this example, when someone browses to example.com, the DNS system will use the A record to resolve example.com to the IP address 192.0.2.1.
Key Points:
- IPv4 Address: A records deal exclusively with IPv4 addresses. For IPv6 addresses, you’d use an AAAA record (often referred to as a “Quad A” record).
- Time-to-Live (TTL): Like other DNS records, A records have a TTL value, which specifies how long the record should be cached by DNS resolvers and browsers. Once the TTL expires, the cache will need to be refreshed.
- Multiple A Records: It’s possible for a domain to have multiple A records. This can be used for various purposes, including load balancing and fault tolerance. When multiple A records are set for a domain, DNS servers often rotate the order in which the addresses are returned, effectively distributing the traffic among the different servers.
Using the A record is fundamental for making websites accessible via their domain names and plays a pivotal role in ensuring that the internet remains user-friendly by allowing people to use easy-to-remember domain names instead of numeric IP addresses.