Create a PTR record for a VM instance

Configurable PTR records let you define the reverse DNS record associated with the external IP address of a VM instance so that applications that rely on these records can operate as intended.

Some applications require reverse DNS records (PTR records) to resolve IP addresses to domain names. For example, applications that use SMTP require a PTR record that points to the domain from which an email is being sent. Without that record, spam filters can mark emails with low reputation, which causes email to end up in spam folders or not be sent at all.

You can add PTR records to only the primary network interface of a VM instance. PTR records are not available for load balancer frontends, Cloud NAT, or other non-VM IP addresses.

IPv6 PTR records are only available if the instance's primary network interface is connected to a dual-stack subnet that has an external IPv6 address range. In this case, you can have separate IPv4 and IPv6 PTR records.

To create custom PTR records that override the automatically created internal DNS PTR names, see Managed reverse lookup zones.

Before you begin

If you haven't already, then set up authentication. Authentication is the process by which your identity is verified for access to Google Cloud services and APIs. To run code or samples from a local development environment, you can authenticate to Compute Engine by selecting one of the following options:

Select the tab for how you plan to use the samples on this page:
Console

When you use the Google Cloud console to access Google Cloud services and APIs, you don't need to set up authentication.
gcloud
1. Install the Google Cloud CLI, then initialize it by running the following command:
```
gcloud init
```
  Note: If you installed the gcloud CLI previously, make sure you have the latest version by running gcloud components update.
2. Set a default region and zone.
REST

To use the REST API samples on this page in a local development environment, you use the credentials you provide to the gcloud CLI.
For more information, see Authenticate for using REST in the Google Cloud authentication documentation.

Verify your domain ownership

Before you create a VM with a custom PTR record, verify that you own the domain name. Verifying ownership is a security measure to prove to Google that you are the domain owner.

You can verify your domain name in 2 ways:

If you have a Google account, you can verify by using Search Console.
If you have a Google or non-Google account, you can verify by adding your VM's IP address to your DNS configuration.

Verify by using Search Console

Open Search Console and sign in by using the Google Account that you will use to add a PTR record to your instance. You can verify domain ownership with multiple accounts.
Enter the PTR domain name.
Click Continue.
Follow the instructions, and then click Go to Property.
Click on Settings (found in the menu on the left near the bottom), and then click Ownership Verification.

After you verify that you own the domain, in the Settings pane, click on Users to see other verified owners. To add PTR records in other domains, click the property picker on the left that displays your current domain. Click Add a property to add those domains.

If your domain name is not immediately verified, use the Recommended Method to obtain verification.

Verify by adding your VM's IP address to your DNS configuration

If your VM does not exist yet, reserve a regional static external IP address and use it later during VM creation.
Add an "A" record with the VM's external IP address to the DNS configuration of your domain.

Create VM instances with PTR records

You can specify PTR records when you create new instances. To add a PTR record for an existing instance, see Add PTR records.

Console

In the Google Cloud console, go to the Create an instance page.

Go to Create an instance
Specify the VM details.
Expand the Advanced options section, and then do the following:
1. Expand the Networking section.
2. Create one or more network interfaces to use with this VM. Alternatively, you can use the default network interface.
3. In the Network interfaces section, expand the first network interface, which is the primary network interface.
4. In the Public DNS PTR record section, select each type of PTR record that you want to add.
5. In the PTR domain name field, enter a domain name for each type of PTR record that you want to add.
6. In the External IPv4 address or External IPv6 address field, choose your previously reserved IP address. If you have verified your VM's IP address through your DNS configuration, then you must specify that address.
7. To confirm the network interface settings, click Done.
Configure the remaining properties for your new VM.
At the bottom of the page, click Create.

After the VM starts, you can run a reverse DNS lookup on the external IP address of your VM to confirm that the PTR record is working as expected.

gcloud

To create a new instance with an associated IPv4 PTR record, use the gcloud instances create command.
```
gcloud compute instances create INSTANCE_NAME \
    --image-family IMAGE_FAMILY \
    --image-project IMAGE_PROJECT \
    --public-ptr \
    --public-ptr-domain DOMAIN_NAME \
    --address=IP_ADDRESS
```
Replace the following:
- INSTANCE_NAME: the name of the new VM instance.
- IMAGE_FAMILY: one of the available image families.
- IMAGE_PROJECT: the Google Cloud project against which all image and image family references are resolved. If you do not supply a project name, the current default project is used.
- DOMAIN_NAME: the domain name to add to this instance.
- IP_ADDRESS: your previously reserved IP address. If you have verified your VM's IP address through your DNS configuration, then you must specify that address.
To create a new instance with an associated IPv6 PTR record, do the following:
1. Create a dual-stack VM.
2. Add an IPv6 PTR record.

REST

To create a new instance with an IPv4 PTR record, make a POST request to the instances.insert method.

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances
{
  "machineType": "zones/ZONE/machineTypes/MACHINE_TYPE",
  "name": "INSTANCE_NAME",
  "disks": [
    {
      "initializeParams": {
        "sourceImage": "projects/debian-cloud/global/images/family/debian-10"
      },
      "boot": true
    }
  ],
  "networkInterfaces": [
    {
      "network": "NETWORK",
      "accessConfigs": [
        {
          "type": "ONE_TO_ONE_NAT",
          "name": "External NAT",
          "natIP": "IP_ADDRESS",
          "publicPtrDomainName": "DOMAIN_NAME",
          "setPublicPtr": true
        }
      ]
    }
  ]
}

Replace the following:

PROJECT_ID: the ID of your project.
ZONE: the zone of your instance.
MACHINE_TYPE: the machine type.
INSTANCE_NAME: the name of the instance.
NETWORK: the URL of the network.
IP_ADDRESS: your previously reserved IP address. If you have verified your VM's IP address through your DNS configuration, then you must specify that address.
DOMAIN_NAME: the domain name to add.

To create a new instance with an IPv6 PTR record, do the following:
1. Create a dual-stack VM.
2. Add an IPv6 PTR record.

Add PTR records

You can add PTR records by updating the access configuration on the primary network interface, nic0, of a VM instance.

Console

In the Google Cloud console, go to the VM instances page.

Go to VM instances
Click the instance that you want to edit.
Click Edit.
In the Network interfaces section, click the primary network interface.
In the Public DNS PTR record section, select each type of PTR record that you want to add.
In the PTR domain name field, enter a domain name for each type of PTR record that you want to add.
Click Done, and then click Save.

gcloud

If your VM doesn't have an access configuration, add one by using the gcloud compute instances add-access-config command.
```
gcloud compute instances add-access-config INSTANCE_NAME
```
Replace INSTANCE_NAME with the name of your instance.
Update the access configuration to add the PTR record by using the gcloud compute instances update-access-config command. To add both IPv4 and IPv6 PTR records, use the following commands individually.
- For IPv4:
```
gcloud compute instances update-access-config INSTANCE_NAME \
    --public-ptr \
    --public-ptr-domain DOMAIN_NAME
```
- For IPv6:
```
gcloud compute instances update-access-config INSTANCE_NAME \
    --ipv6-public-ptr-domain=DOMAIN_NAME
```
Replace the following:
- INSTANCE_NAME: the name of the instance to update.
- DOMAIN_NAME: the domain name to add.

REST

If your VM doesn't have an access configuration, add one by making a POST request to the instances.addAccessConfig method.

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances/INSTANCE_NAME/addAccessConfig?networkInterface="nic0"

Update the access configuration to add the PTR record by making a POST request to the instances.updateAccessConfig method. To add both IPv4 and IPv6 PTR records, make the following requests individually.

For IPv4:

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances/INSTANCE_NAME/updateAccessConfig?networkInterface=nic0
{
  "setPublicPtr": true,
  "publicPtrDomainName": "DOMAIN_NAME",
  "type": "ONE_TO_ONE_NAT"
}

For IPv6:

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances/INSTANCE_NAME/updateAccessConfig?networkInterface=nic0
{
  "publicPtrDomainName": "DOMAIN_NAME",
  "type": "DIRECT_IPV6"
}

Replace the following:

PROJECT_ID: the project ID.
ZONE: the zone of the instance.
INSTANCE_NAME: the instance name.
DOMAIN_NAME: the domain name to add.

Remove PTR records

To remove PTR records, update the access configuration on the primary network interface, nic0, of a VM instance. When you remove a PTR record, Google Cloud responds to reverse DNS lookups with a default fully qualified domain name of googleusercontent.com.

Console

In the Google Cloud console, go to the VM instances page.

Go to VM instances
Click the instance that you want to edit.
Click Edit.
In the Network interfaces section, click the primary network interface.
In the Public DNS PTR record section, clear the checkbox for each type of PTR record that you want to remove.
Click Done, and then click Save.

gcloud

To remove a PTR record, use the gcloud compute instances update-access-config command. To remove both IPv4 and IPv6 PTR records, use the following commands separately.

For IPv4:

gcloud compute instances update-access-config INSTANCE_NAME \
    --no-public-ptr

For IPv6:

gcloud compute instances update-access-config INSTANCE_NAME \
    --no-ipv6-public-ptr

Replace INSTANCE_NAME with the name of the instance to update.

REST

To remove a PTR record, make a POST request to the instances.updateAccessConfig method. To remove both IPv4 and IPv6 PTR records, make the following requests individually.

For IPv4:

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances/INSTANCE_NAME/updateAccessConfig?networkInterface=nic0
{
  "setPublicPtr": false,
  "type": "ONE_TO_ONE_NAT"
}

For IPv6:

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances/INSTANCE_NAME/updateAccessConfig?networkInterface=nic0
{
  "publicPtrDomainName": "",
  "type": "DIRECT_IPV6"
}

Replace the following:

PROJECT_ID: the project ID.
ZONE: the zone of the instance.
INSTANCE_NAME: the instance name.

Limitations

When a VM is migrated to another host as part of the live migration process during maintenance events, the PTR record logic doesn't handle some edge cases correctly and reverts the DNS PTR records to the fully qualified domain name (FQDN) googleusercontent.com. To restore functionality, apply the PTR record again.
When you stop a VM that has an IPv6 PTR record, the IPv6 PTR record is temporarily deregistered and not visible on the VM. The record is added back automatically when you restart the VM.

What's next

For an overview of how to configure and manage static external IP addresses for your resources, see Reserve a static external IP address.
To learn how to create and manage virtual machine instances, see Create and start a VM instance.