A and AAAA Records: How Your Domain Name Becomes an IP Address

When you type a domain name into a browser, a translation happens before your request goes anywhere. The browser needs an IP address, a specific network location, to connect to. The DNS record that provides it is the A record.

Everything else in DNS can be working perfectly, but without a correct A record pointing at a live server, your website is unreachable.

What an A record does

An A record maps a hostname to an IPv4 address, the four-number format most people recognize:

example.com.    A    203.0.113.42

This tells resolvers: when someone requests example.com, send them to 203.0.113.42. Your server is listening there, and that's where the browser makes its connection.

Most domains have at least two A records: one for the root domain (example.com) and one for www (www.example.com). These can point at the same IP address or different ones, depending on how the site is set up.

Subdomains get their own A records too. blog.example.com, api.example.com, and app.example.com can all point at different servers. Each is an independent record that can be changed without affecting the others.

What AAAA records do

AAAA records do the same thing as A records, but for IPv6 addresses, the longer, newer format:

example.com.    AAAA    2001:0db8:85a3::8a2e:0370:7334

IPv4 addresses come in roughly 4 billion combinations. That sounds like a lot, but the internet ran out of unallocated IPv4 space years ago. IPv6 was designed to solve this, with enough addresses for every device that will ever exist, several times over.

Most modern servers and hosting providers support both. When a domain has both an A record and an AAAA record, browsers and other clients prefer the IPv6 address if the visitor's network supports it, and fall back to IPv4 if it doesn't. From a user's perspective, nothing changes. The same site loads either way.

Some domains only publish A records. That's common and fine. Publishing AAAA records is a matter of whether your server and hosting setup support IPv6. You don't need both, but having both means IPv6-only networks, increasingly common on mobile, can reach your site directly.

When A records legitimately change

The normal reasons A records change:

Moving to a new server or host. Migrating your site to a new provider means updating your A record to point at the new server's IP. This is the most common reason for an A record change and should happen alongside a planned migration.

Switching to a CDN. Content delivery networks like Cloudflare and Fastly sit in front of your server and serve traffic from locations close to each visitor. When you enable a CDN, your A records typically change from your server's IP to the CDN's IP addresses. When you remove a CDN, they change back.

Autoscaling infrastructure. Cloud instances and containerized deployments that don't use static IPs can be assigned a new IP address on restart or redeployment. A record changes in these environments can be intentional and frequent.

Correcting a misconfiguration. A typo in an IP address, a record that was never cleaned up, or a stale entry pointing at a decommissioned server are all things that eventually get fixed.

What an unexpected A record change means

An A record change redirects all traffic to your domain to a different server.

Unlike an MX change that silently affects email, a changed A record is immediately visible: your site either goes down or serves someone else's content. There's no error page from your host. The connection just goes to whatever is running at the new IP address.

The malicious version is DNS hijacking: an attacker who gains access to your DNS can point your A record at a server they control. Visitors who reach that server see whatever the attacker puts there: a phishing page, a credential-harvesting login form, or a replica of your site designed to intercept submissions. Because the domain name in the browser bar still looks correct, many users won't notice.

Even without malicious intent, a wrong A record is immediately disruptive. A mistyped IP address, a record overwritten during a migration, or a provider error can take a site offline with no warning. The domain still resolves. It just resolves to the wrong place.

How to check your A records

To see what a public resolver currently returns for your domain:

dig A example.com

To query a specific resolver, bypassing your local cache:

dig @8.8.8.8 A example.com

To check AAAA records:

dig AAAA example.com

The response will show the IP address, the TTL remaining before the cache expires, and which nameserver answered. If you don't have dig, dnschecker.org will show results from multiple global locations without installing anything.

How DNS monitoring fits in

A record changes have the most immediate, visible impact of any record type. An unexpected change doesn't generate a server error or a broken deployment notification. The infrastructure looks fine from the inside. The only signal is that traffic is going somewhere it shouldn't.

OneDollarDNS monitors A and AAAA records alongside every other record type and alerts you the moment anything changes, so an unexpected redirect shows up as an alert before it shows up as a user reporting your site is down, or worse, showing them something it shouldn't.