Host Reverse DNS PTR Records in UltraDNS – UltraDNS Support

This article explains how to host reverse DNS PTR records in UltraDNS after the applicable reverse DNS zone has been delegated to UltraDNS name servers.

When to Use This Article

Use this article when you need UltraDNS to answer reverse DNS lookups for an IP address, such as a lookup using dig -x.

Reverse DNS is not controlled by the forward DNS zone for your domain. Reverse DNS is controlled by the organization that owns or manages the IP address block, usually the ISP, hosting provider, or IP address provider.

Before You Begin

UltraDNS can host a PTR record only when the applicable reverse DNS zone exists in UltraDNS and the reverse DNS zone has been delegated to UltraDNS name servers.

Contact your ISP, hosting provider, or IP address provider before creating the PTR record in UltraDNS.

Ask them to provide the exact reverse DNS zone name that has been delegated to UltraDNS.

If the provider cannot delegate the reverse DNS zone to UltraDNS, ask the provider to create the PTR record on your behalf.

Reverse DNS Example

For the IPv4 address 1.2.3.4, a standard /24 reverse DNS delegation would commonly use the following values:

IP address: 1.2.3.4
Reverse DNS zone: 3.2.1.in-addr.arpa
PTR record name inside the zone: 4
Full PTR owner name: 4.3.2.1.in-addr.arpa
PTR target: mail.example.com.

The reverse DNS zone name may be different for non-standard or classless delegations.

Use the exact reverse DNS zone name provided by the ISP, hosting provider, or IP address provider.

Add the Reverse DNS Zone in UltraDNS

Log in to the UltraDNS Portal.
Select Domains from the navigation menu.
Select Add Domain.
In the Domain Name field, enter the exact reverse DNS zone name provided by your ISP or IP address provider.

Example:
```
3.2.1.in-addr.arpa
```
In the Type drop-down menu, select Primary.
Under Record Import, select None unless you are importing an existing zone file.
Select Save.

Add the PTR Record

Open the reverse DNS zone that was added in UltraDNS.
Add a PTR record.
- In grouped view, expand PTR records if needed, and then select Add Record.
- In table view, use the Add Record drop-down menu and select PTR.
In the In-Addr field, enter the PTR record name for the reverse DNS zone.

For a standard /24 reverse DNS zone, this is the last octet of the IP address.

Example:
```
IP address: 1.2.3.4
Reverse DNS zone: 3.2.1.in-addr.arpa
In-Addr value: 4
Full PTR owner name: 4.3.2.1.in-addr.arpa
```
You can also enter the full reverse address when needed.
```
4.3.2.1.in-addr.arpa.
```
In the Points To field, enter the hostname that should be returned by the reverse lookup.

Example:
```
mail.example.com.
```
Use a fully qualified hostname. A trailing dot is recommended when entering the complete hostname.
Set the TTL value as needed, or leave the field empty to use the configured default value.
Select Save.

Verify the PTR Record

After the reverse DNS zone is delegated and the PTR record is created, run a reverse lookup for the IP address:

dig -x 1.2.3.4

The response should return the hostname entered in the Points To field.

Expected Outcome

UltraDNS returns the PTR record only when the reverse DNS zone is delegated to UltraDNS name servers and the PTR record exists in the delegated reverse DNS zone.

Important Notes

PTR records must be created in the applicable reverse DNS zone, not in the forward DNS zone.
Hosting a forward DNS zone in UltraDNS does not automatically mean UltraDNS hosts reverse DNS for the related IP address.
The reverse DNS zone added in UltraDNS must match the zone delegated by the ISP, hosting provider, or IP address provider.
For IPv4 address a.b.c.d, the full PTR owner name is d.c.b.a.in-addr.arpa.
For a standard /24 reverse DNS zone, the reverse DNS zone is usually c.b.a.in-addr.arpa, and the PTR record name inside that zone is d.
Do not confuse the full PTR owner name with the reverse DNS zone name.
You cannot always determine the correct reverse DNS zone name from the IP address alone, especially for IP ranges smaller than a /24. Confirm the delegated reverse DNS zone name with the ISP, hosting provider, or IP address provider.

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