How Can I Configure a PTR Record to Map the IP Address of an ECS to a Domain Name?

PTR records enable users to query domain names based on IP addresses.

To map the private IP address of an ECS to a domain name, you must create a private zone and create a PTR record in the zone.

The domain name in a PTR record must be in the x.x.x.x.in-addr.arpa format. in-addr.arpa is the domain name suffix used for reverse resolution.

For example, if the private IP address is 192.168.1.10, the domain name in the PTR record must be 10.1.168.192.in-addr.arpa.

In this case, you must create a private zone named 192.in-addr.arpa and add a PTR record with its value set to 10.1.168.192.in-addr.arpa.

Creating a Private Zone

Log in to the management console.
In the service list, choose Network > Domain Name Service.
The DNS console is displayed.
In the navigation pane, choose Private Zones.
The Private Zones page is displayed.
Click in the upper left corner and select the desired region and project.
Click Create Private Zone.

Configure the parameters based on Table 1.

**Table 1** Parameters for creating a private zone
Parameter	Description	Example Value
Name	Domain name Set the domain name suffix to in-addr.arpa.	192.in-addr.arpa
VPC	VPC to be associated with the private zone Select the VPC you want to associate with the private zone.	N/A
Email	(Optional) Email address of the administrator managing the private zone. Recommended email address: HOSTMASTER@Domain name For more information about the email address, see Why Was the Email Address Format Changed in the SOA Record?	HOSTMASTER@example.com
Enterprise Project	Enterprise project associated with the private zone. You can manage private zones by enterprise project. NOTE: This parameter is available and mandatory only when Account Type is set to Enterprise Account. When setting this parameter, note the following: If you do not manage zones by enterprise project, select the default enterprise project. If you manage zones by enterprise project, select an existing enterprise project.	default
Tag	(Optional) Identifier of a resource Each tag contains a key and a value. You can add a maximum of 10 tags to a zone. For details about tag key and value requirements, see Table 2.	example_key1 example_value1
Description	(Optional) Supplementary information about the zone You can enter a maximum of 255 characters.	This is a private zone.

**Table 2** Tag key and value requirements
Parameter	Requirements	Example Value
Key	Cannot be left blank. Must be unique for each resource. Can contain a maximum of 36 characters. Cannot start or end with a space or contain special characters =*<>\,\|/	example_key1
Value	Cannot be left blank. Can contain a maximum of 43 characters. Cannot start or end with a space or contain special characters =*<>\,\|/	example_value1

Click OK.
Switch back to the Private Zones page.
View the created private zone.
Click the zone name to view zone details. You can view SOA and NS record sets automatically generated by the system.
- The SOA record set defines the DNS server that is the authoritative information source for a particular domain name.
- The NS record set defines authoritative DNS servers for a domain name.

Adding a PTR Record

On the Private Zones page, click the name of the private zone that you have created.
The Record Sets page is displayed.
Click Add Record Set.
The Add Record Set dialog box is displayed.

Configure the parameters based on Table 3.

**Table 3** Parameters for adding a PTR record
Parameter	Description	Example Value
Name	IP address in the PTR record (typed in reverse order).	10.1.168 For example, if the IP address is 192.168.1.10, the domain name in the PTR record is 10.1.168.192.in-addr.arpa. If the private zone name is 192.in-addr.arpa, enter 10.1.168 in the box. If the private zone name is 1.168.192.in-addr.arpa, enter 10 in the box.
Type	Type of the record set.	PTR – Map IP addresses to domains
TTL (s)	Cache duration of the record set, in seconds.	The default value is 300s, which is, 5 minutes.
Value	Domain name mapped to the IP address. You can enter only one name.	mail.example.com
Tag	(Optional) Identifier of a resource Each tag contains a key and a value. You can add a maximum of 10 tags to a record set. For details about tag key and value requirements, see Table 2.	example_key1 example_value1
Description	(Optional) Supplementary information about the PTR record.	The PTR record is for reverse resolution.

Click OK.
Switch back to the Record Sets page.
View the added record set in the record set list of the zone and ensure that the status of the record set is Normal.