A PTR (pointer) record maps an IP address to a domain name, enabling reverse DNS lookups. It reverses the direction of an A record lookup. section 3.1.5 section 3.3
Table 3.1 DNS record types (view table figure)
| Record type |
Description |
Example |
|---|---|---|
| A |
Points to an IPv4 address |
example.com -> 192.0.2.1 |
| AAAA |
Points to an IPv6 address |
example.com -> 2001:db8::1 |
| CNAME |
Points to another domain name |
www.example.com -> example.com |
| MX |
Specifies the domain’s mail server(s) |
example.com -> mail1.example.com |
| NS |
Specifies the domain’s authoritative DNS server(s) |
example.com -> ns1.example.com |
| PTR |
Used for reverse DNS lookups, mapping an IP address back to a domain name |
192.0.2.1 -> example.com |
| SOA |
Provides administrative information such as admin contact details, a serial number, etc. |
example.com -> Admin: admin.example.com; Serial: 123456789; etc. |
Compare PTR records with A, AAAA, CNAME, MX, NS, and SOA records, including the example mapping 192.0.2.1 to example.com. section 3.1.5
Exam-relevant facts:
- Use PTR records for reverse DNS resolution: finding the domain name associated with a particular IP address. section 3.1.5
- Distinguish PTR records from A records: PTR maps IP addresses to domain names, while A maps domain names to IPv4 addresses. section 3.1.5 section 3.3
