DNS A Records Explained: How Domains Map to IPv4

The A record is the most consequential line in your DNS zone. It maps a hostname to an IPv4 address, and if it is wrong or missing, your site is unreachable no matter how perfectly everything else is configured.

A stands for Address. Its IPv6 sibling is the AAAA record (spoken "quad-A"), named because an IPv6 address is four times the size of an IPv4 one.

Anatomy of an A record

example.com.      3600    IN    A       93.184.216.34
www.example.com.  3600    IN    A       93.184.216.34
example.com.      3600    IN    AAAA    2606:2800:220:1::248

Reading left to right:

A versus AAAA

These are not alternatives — publish both. A dual-stack client will typically prefer IPv6 and fall back to IPv4, so having both gives every visitor a working path. Publishing only an A record leaves IPv6-only clients, which do exist on some mobile networks, unable to reach you at all.

Multiple A records for one name

A hostname can have several A records. Resolvers hand out all of them, typically rotating the order, which spreads traffic across servers — classic round-robin DNS.

example.com.    300    IN    A    93.184.216.34
example.com.    300    IN    A    93.184.216.35
example.com.    300    IN    A    93.184.216.36

It is crude load balancing: DNS has no idea whether a server is healthy, so a dead address keeps being handed out until you remove the record. Why a domain has multiple IPs covers the better alternatives.

The four mistakes that break sites

1. 1

   Forgetting the www record

   example.com and www.example.com are different hostnames requiring separate records. Setting one and not the other means half your visitors hit a dead name.

2. 2

   Editing records at the wrong provider

   If your NS records delegate to your host, records edited at your registrar are ignored entirely. Check which nameservers are authoritative first.

3. 3

   Leaving the TTL high before a migration

   Changing an A record with an 86400-second TTL means up to 24 hours of split traffic. Lower the TTL a day before you move.

4. 4

   Keeping a stale A record alongside a CNAME

   A name may not have both a CNAME and other records. Many providers silently ignore one, producing inconsistent behaviour.

Wildcards, subdomains, and the apex

Three naming situations come up constantly and behave differently enough to be worth separating.

The apex (root) record

The apex is the bare domain, example.com, with no subdomain. In most control panels it is written @. It is the one name where you frequently must use an A record rather than a CNAME, because the protocol forbids a CNAME coexisting with the NS and SOA records the apex is required to carry.

Subdomain records

Every subdomain is an independent name needing its own record. www, blog, shop, and api do not inherit anything from the apex — setting an A record on example.com does nothing whatsoever for www.example.com.

Wildcard records

A wildcard answers for any name that has no record of its own.

*.example.com.    3600    IN    A    93.184.216.34

Useful for multi-tenant products where each customer gets their-name.example.com without a DNS change per signup. Two caveats worth knowing before you reach for one:

• An explicit record always wins. If api.example.com has its own A record, the wildcard is not consulted for that name.
• A wildcard only covers one level. *.example.com matches foo.example.com but not foo.bar.example.com.

Checking your A records

dig +short example.com A
dig +short example.com AAAA

Or resolve both at once with the lookup tool, which queries A and AAAA independently and lists them separately, so you can immediately see whether IPv6 is actually configured.