The Domain Name System (DNS) uses different types of records for name resolution, including MX (mail), TXT (various). The A and AAAA records are used to match a domain to an IPv4 and IPv6 address, respectively:
| Type | Entry | Pointer |
|---|---|---|
| A | example.org | 192.0.2.42 |
| AAAA | example.org | 2001:db8:1234::42 |
| A | vpn.example.org | 192.0.2.137 |
In this case, the domain example.org will be resolved to a different IP than vpn.example.org , and the latter only being reachable through IPv4.
In addition, there exist CNAME records which allow to point a domain to another domain, triggering a an A/AAAA record lookup only through indirection:
| Type | Entry | Pointer |
|---|---|---|
| CNAME | www.example.org | example.org |
Here, the www-subdomain www.example.org should point to whatever the second level domain should point to.