Domains and DNS

What is a DNS A record?

Every other DNS record exists to eventually point somewhere, and an A record is where the pointing stops.

An A (Address) record maps a host name to an IPv4 address, written as four numbers from 0 to 255 separated by dots, such as 93.184.216.34. It is the most basic record type in DNS and the one a browser ultimately needs before it can open a TCP connection to anything. Its IPv6 counterpart is the AAAA record (see IPv4 vs IPv6); its counterpart for aliasing one name to another instead of an address is the CNAME record.

Worked out 2026-09-18 (IST) · IPv4 addressing and standard DNS resolution as specified in RFC 1035

What an A record actually contains

An A record has exactly four parts, and a DNS lookup tool shows all of them:

Anatomy of an A record
Field	Example	What it means
Name	www.example.com	The host being resolved
Type	A	Fixed - tells the resolver to expect an IPv4 address
Value	93.184.216.34	The IPv4 address, in dotted-quad form
TTL	3600	Seconds a resolver may cache this answer before asking again

A record vs its three closest relatives

Which record does which job
Record	Points to	Used for
A	An IPv4 address	The basic host-to-address mapping
AAAA	An IPv6 address	Same job, for IPv6 - see IPv4 vs IPv6
CNAME	Another host name	Aliasing - see CNAME record
MX	A mail server host name (with a priority)	Where email for the domain goes - see MX record

Why one A record is not always enough

A single web server behind a single A record is a single point of failure. Sites that need either more capacity or more resilience publish several A records for the same name, and rely on round-robin selection - or, more often today, put a load balancer or a CDN edge network in front and let it hold the A record instead, so the record itself never changes even as the servers behind it do.

What actually breaks when an A record is wrong

Symptom to cause
Symptom	Most likely cause
Site unreachable, "cannot resolve host"	A record missing, or the domain’s name servers are wrong
Some visitors reach the old server after a migration	Old A record still cached by their resolver - it will clear once the TTL expires
Works on some networks, not others	A record was updated at the registrar but not propagated to every resolver yet - see DNS propagation

Checking a domain’s current A record is the first step in almost any DNS diagnosis - see how to check DNS records for a domain for the full method.

Sources: IETF RFC 1034 and RFC 1035 (domain names), RFC 2181 (clarifications to the DNS specification), RFC 5321 (SMTP) and RFC 7505 (null MX).

Check your own numbers

Look up the live A records for any domain, alongside its AAAA, MX and TXT records.

DNS LookupA, AAAA, MX, NS, TXT, CNAME and SOA records, live from the resolver.

Frequently asked

Can a domain have more than one A record?

Yes, and it is a normal, deliberate pattern called round-robin DNS. A resolver that gets back three A records picks one - usually the first, though some resolvers rotate or randomise - and if that server stops answering, later lookups can land on a different address. It is a crude form of load balancing and basic failover, not a guarantee of either.

What is the difference between an A record and a CNAME?

An A record is an address: the value is an IP number. A CNAME is an alias: the value is another host name that itself has to be looked up. A resolver following a CNAME chain always ends at an A or AAAA record eventually - a CNAME can never terminate a DNS query on its own, only redirect it.

How fast does a change to an A record take effect?

As fast as the record’s TTL allows and not a second faster, because any resolver that already cached the old value keeps serving it until that TTL expires. See <a href="/answers/what-is-dns-ttl/">what TTL means</a> for how to plan a migration around it.

Does an A record work for an IPv6 address?

No. An A record can only hold an IPv4 address. A host that also needs to be reachable over IPv6 needs a separate AAAA record pointing at its IPv6 address - the two record types coexist under the same name and a dual-stack resolver can return both.

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