Set up reverse DNS

Reverse DNS gives a public IPv4 address a name, so that someone who looks up the address gets that name back. Mail servers often check it before they accept mail, so a server that sends mail needs reverse DNS set to its own name, such as mail.example.com.

Every E2E public IP already has a default reverse name, set by E2E. A custom reverse DNS record replaces it with your name. You add it yourself in MyAccount, on Manage Reverse DNS.

Before you begin

• The address is the public IP of one of your nodes, or one of your reserved IPs. Reverse DNS is for IPv4 addresses only. See Node and Reserved IP.
• You have chosen the name, a host name you control, such as mail.example.com or www.example.com, up to 100 characters.
• The name resolves to the address. It must have an A record that points to that IP, live on public DNS. The A record can be on E2E DNS or at any other DNS provider. See Add a DNS record.
• Your role in the project lets you create resources, which is what shows Add Reverse DNS.

To check that the name resolves to the address, run this, with your name in place of mail.example.com:

dig mail.example.com A +short

The output must be the address you are setting reverse DNS for, such as 203.0.113.10. An empty output means the name has no A record yet. A new A record can take a while to show, until any older answer’s TTL runs out.

Open Manage Reverse DNS

In MyAccount, under Network, click DNS, and on Manage DNS, click Add Reverse DNS. Manage Reverse DNS opens.

It lists each address you can set reverse DNS for, with Host, TTL, Record Type, and Value. Host is the address written backwards with in-addr.arpa. at the end: 203.0.113.25 is listed as 25.113.0.203.in-addr.arpa.. That is how DNS stores reverse names. Value is the address’s current name: its default name until you add your own. Search Reverse DNS finds an address by either.

Add the reverse DNS record

1. On Manage Reverse DNS, click Add Record. The Add Reverse Domain dialog opens.
2. Under IPv4 Address, choose the address from the list. It holds the public IPs of your nodes, in every project, and the reserved IPs of the project you are in. To set reverse DNS for a reserved IP in another project, switch to that project first.
3. In Domain, enter the name you want the address to return, such as mail.example.com.
4. Click Submit.

You see The custom Reverse DNS record was created successfully!, and the address’s Value on Manage Reverse DNS changes to your name. A new reverse DNS record has a TTL of 86400 seconds, which is one day.

These messages tell you what to change:

• mail.example.com. does not point to 203.0.113.10, with your name and address: the name’s A record points to another address. Correct the A record, wait until dig shows the right address, and add the reverse DNS again.
• The forward record mail.example.com. 203.0.113.10 does not exist: the name has no A record on public DNS. Add one that points to the address, and try again.
• Domain name you have specified is not valid.: check the name, such as mail.example.com.
• No available PTR record was found for this IP. Please verify the IP address and try again., when you open Add Reverse Domain: you have no node or reserved IP to choose. Create a node or reserve an IP first, in this project for a reserved IP.
• Custom Reverse DNS record already exist: see Custom Reverse DNS record already exist.

Check the reverse name

To look the address up the way a mail server does, run:

dig -x 203.0.113.10 +short

The output is your name, with a dot at the end:

mail.example.com.

If it still shows the default name, run the command again later. Then check both directions together: dig -x gives your name, and dig mail.example.com A +short gives the same address.

Your address now returns your own name. For the mail records that go with it, see Set up email records. For help with any message, see Troubleshooting DNS.