What Is Reverse Resolution?

Generally, DNS resolves a domain name to an IP address. When you access a website using a domain name, DNS maps the domain name to the IP address of the web server where the website is deployed.

Reverse resolution, on the opposite, is a query in which a domain name connected with an IP address is returned. It is usually used in scenarios such as anti-spam and logging.

• Anti-spam: queries the domain name based on the IP address of the sender's mail server to obtain the reputation of the domain name.
• Logging: queries the domain name or host name based on the IP address to distinguish service data.

To obtain a domain name from a private IP address, you need to create a private zone for top-level domain in-addr.arpa. For example, if the IP address 192.0.2.255, the domain name for the PTR record can be 255.2.0.192.in-addr.arpa.

By default, each EIP supports reverse resolution, and its domain name for the PTR record is in the format of ecs-x-x-x-x.compute.hwclouds-dns.com. By pinging each EIP, you can obtain its default domain name. You can create a PTR record for the EIP to overwrite the default domain name.