How DNS Lookup Works: A and AAAA Records Explained

The DNS Hierarchy

The Domain Name System is a distributed database organised as a hierarchy. At the top are the root nameservers (13 sets, operated by different organisations). Below them are TLD nameservers (for .com, .net, .io, etc.). Below them are authoritative nameservers for individual domains.

The Resolution Process

When you visit profittool.io:

1. Your browser checks its local cache.
2. If not cached, it asks your operating system's resolver.
3. The resolver asks a recursive resolver (usually your ISP or 8.8.8.8).
4. The recursive resolver asks the root nameserver: "Who handles .io?"
5. The root returns the .io TLD nameserver addresses.
6. The recursive resolver asks the .io TLD: "Who handles profittool.io?"
7. The TLD returns the authoritative nameservers for profittool.io.
8. The recursive resolver asks the authoritative nameserver for the A record.
9. The authoritative nameserver returns the IP address.
10. The recursive resolver caches the result (for the duration of the TTL) and returns it to your browser.

A Records (IPv4)

An A record maps a domain name to an IPv4 address:

profittool.io    300    IN    A    104.21.42.100

The number 300 is the TTL (Time To Live) in seconds — how long resolvers may cache this answer.

AAAA Records (IPv6)

An AAAA record maps a domain name to an IPv6 address:

profittool.io    300    IN    AAAA    2606:4700:3031::6815:2a64

The four-A name reflects that an IPv6 address is four times longer than IPv4.

TTL and Propagation

When you change a DNS record, the change propagates only after the old TTL expires. Resolvers that cached the old record continue serving it until their cached copy expires. This is why DNS changes can take minutes to hours to propagate globally, depending on the TTL value.

Use our DNS Lookup tool to inspect any domain's A, AAAA, MX, TXT, NS, CNAME, SOA and CAA records instantly.