Host IPv4 Reverse DNS PTR Records in UltraDNS – UltraDNS Support

Overview

This article explains how to host IPv4 reverse DNS PTR records in UltraDNS.

A PTR record can be configured in UltraDNS after the applicable reverse DNS zone has been added to your UltraDNS account. Public reverse DNS lookups are directed to UltraDNS only after the organization responsible for the IP address block delegates the reverse DNS zone to the applicable UltraDNS nameservers.

When to Use This Article

Use this article when:

You need UltraDNS to provide the PTR record for an IPv4 address.
Your ISP, hosting provider, or IP address provider can delegate the applicable reverse DNS zone to UltraDNS.
You need to verify the PTR record by using a reverse lookup such as dig -x.

Reverse DNS is not controlled by the forward DNS zone for your domain. Reverse DNS is controlled by the organization responsible for the applicable IP address block, such as an ISP, hosting provider, or IP address provider.

Before You Begin

Contact your ISP, hosting provider, or IP address provider before configuring the reverse DNS zone in UltraDNS.

Ask the provider to confirm:

Whether the reverse DNS zone can be delegated to UltraDNS.
The exact reverse DNS zone name that must be added to UltraDNS.
The UltraDNS nameservers to which the provider will delegate the zone.

The reverse DNS zone configured in UltraDNS must exactly match the zone delegated by the provider.

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 configuration would 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 can be different for a classless IPv4 delegation, including an IP range smaller than a /24. 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, hosting provider, or IP address provider.

Example:
```
3.2.1.in-addr.arpa
```
In the Type drop-down menu, select Primary.
If your user has access to multiple accounts, select the account in which the reverse DNS zone should be created.
Under Record Import, select None unless you are importing an existing reverse zone file.
Select Save Changes.

Add the PTR Record

Open the reverse DNS zone that was added to 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 within the reverse DNS zone.

For a standard /24 reverse DNS zone, this is the final octet of the IPv4 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.
```
UltraDNS also accepts the complete IPv4 reverse owner name in the In-Addr field.
```
4.3.2.1.in-addr.arpa.
```
In the Points To field, enter the fully qualified hostname that the reverse lookup should return.

Example:
```
mail.example.com.
```
Set the TTL value as needed, or leave the field empty to use the configured default TTL.
Select Save.

Verify the Reverse DNS Delegation

Confirm that the applicable reverse DNS zone is delegated to the UltraDNS nameservers assigned to the zone.

You can trace the reverse lookup delegation with:

dig -x 1.2.3.4 +trace

The delegation path must reach the applicable UltraDNS nameservers. If the delegation points to another DNS provider, public reverse lookups will not use the PTR record configured in UltraDNS.

Verify the PTR Record

After the reverse DNS zone has been delegated and the PTR record has been created, run:

dig -x 1.2.3.4

The answer should contain the fully qualified hostname entered in the Points To field.

Expected Outcome

Public recursive reverse DNS lookups for the IPv4 address reach the delegated UltraDNS reverse zone and return the configured PTR target.

If the PTR record exists in UltraDNS but the reverse DNS zone is not delegated to UltraDNS, public recursive lookups will not reach the UltraDNS zone.

Important Notes

PTR records must be created in the applicable reverse DNS zone, not in the forward DNS zone that contains the hostname.
Hosting a forward DNS zone in UltraDNS does not automatically make UltraDNS authoritative for reverse DNS associated with the zone's IP addresses.
For IPv4 address a.b.c.d, the complete PTR owner name is d.c.b.a.in-addr.arpa.
For a standard /24 reverse DNS zone, the zone is c.b.a.in-addr.arpa, and the relative PTR record name is d.
Do not confuse the complete PTR owner name with the reverse DNS zone name.
For a classless IPv4 delegation, the provider can use CNAME records in the parent reverse zone and a provider-defined child-zone name. Use the exact zone name and PTR owner format supplied by the provider.
This procedure documents IPv4 reverse DNS under in-addr.arpa. IPv6 reverse DNS uses ip6.arpa and is not covered by this procedure.

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