What is A Record?
A DNS resource record that maps a hostname to a 32-bit IPv4 address. It is the most fundamental record type for translating domain names to numeric addresses on the Internet.
An A record (address record) is a DNS resource record that maps a fully qualified domain name (FQDN) to an IPv4 address. When a client queries a DNS resolver for a hostname (for example, www.example.com), the resolver returns the IPv4 address stored in the A record, allowing the client to establish a TCP/IP connection. Each A record is a single mapping; if a hostname has multiple IP addresses, multiple A records are created, and the resolver may use round-robin or other load-balancing logic.
A records are stored in zone files on authoritative name servers. The record has a name, a type field (value 1), a class (typically IN for Internet), a TTL specifying how long the record can be cached, and an RDATA field containing a 32-bit IPv4 address in dotted-decimal notation (for example, 192.0.2.1). The resolver obtains the A record via iterative or recursive queries. The record supports wildcard entries, where a name starting with "*." matches any unlisted subdomain. The A record is the historical foundation of DNS, established in RFC 1035, and remains the most heavily used record type for direct hostname-to-IP resolution.
In the wider network stack, A records sit between application-layer protocols (HTTP, SMTP, FTP) and the routing infrastructure. The client first resolves the domain via DNS (often using A records), then uses the returned IP address for transport-layer communication. The A record is complemented by the AAAA record for IPv6 and by the CNAME record for aliasing, but it remains irreplaceable for IPv4 connectivity.
Key facts
- Stores a hostname to IPv4 address mapping in DNS.
- Record type value is 1 per RFC 1035.
- IPv4 address is 32 bits, written in dotted-decimal notation.
- Multiple A records for one hostname enable DNS-based load balancing.
- Wildcard A records use a leading asterisk to match unspecified subdomains.
How it works in practice
Related terms
References
More in DNS
AAAA Record
A DNS resource record that maps a hostname to a 128-bit IPv6 address, analogous to the A record for IPv4.
Authoritative DNS
An authoritative DNS server holds the definitive resource records for a specific domain and responds to queries with the final answer for that zone, not a cached copy.
CAA Record
A CAA (Certification Authority Authorization) DNS record lets domain owners specify which certificate authorities are permitted to issue SSL/TLS certificates for their domain.
CNAME Record
A DNS record that maps an alias hostname to the true or canonical hostname, allowing multiple names to resolve to the same IP address without duplicating A or AAAA records.
DNS
The Domain Name System (DNS) is a hierarchical, distributed naming system that translates human-readable domain names (like example.com) into IP addresses and other resource records used by internet protocols.
DNS Anycast
DNS Anycast uses one IP address served from multiple geographically distributed nameservers; queries are routed to the nearest or healthiest node, improving resilience and reducing latency.
DNS Caching
DNS caching stores resolved domain name query results for the specified TTL duration to avoid repeated queries to upstream authoritative servers.
DNS Hijacking
DNS hijacking is an attack or misconfiguration that returns forged DNS responses, causing users to connect to attacker-controlled hosts instead of the intended server.
DNSSEC
DNSSEC (DNS Security Extensions) add cryptographic digital signatures to DNS records, enabling resolvers to verify that responses have not been tampered with or spoofed.
DoH
DNS over HTTPS (DoH) encrypts DNS queries and responses inside HTTPS traffic, preventing on-path observers from seeing or tampering with DNS lookups.