Why PTR Records May Not Be Managed in UltraDNS

This article explains why UltraDNS can host forward DNS for your domain while reverse DNS for the related IP address is managed somewhere else.

Use this article when you manage an A or AAAA record in UltraDNS but cannot create, update, or resolve the corresponding PTR record for the IP address.

When to Use This Article

You manage your forward DNS zone in UltraDNS.
You created an A or AAAA record but cannot configure the corresponding PTR record.
You are troubleshooting reverse DNS resolution.
You need to understand why forward DNS and reverse DNS are handled separately.

What This Means

Forward DNS maps a hostname to an IP address.

This is usually done with an A record for IPv4 or an AAAA record for IPv6.

Example forward DNS record:

ccvse.stc.com.bh A 37.131.69.228

Reverse DNS maps an IP address back to a hostname. This is done with a PTR record.

Example reverse DNS record:

228.69.131.37.in-addr.arpa PTR ccvse.stc.com.bh.

Forward DNS and reverse DNS are delegated separately.

Hosting the forward DNS zone in UltraDNS does not automatically mean UltraDNS also hosts reverse DNS for the related IP address.

How IPv4 Reverse DNS Works

Reverse DNS for IPv4 uses the in-addr.arpa namespace.

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 delegation, the reverse DNS zone is usually c.b.a.in-addr.arpa, and the PTR record name inside that zone is d.

Example

IP address:

37.131.69.228

Forward DNS record:

ccvse.stc.com.bh A 37.131.69.228

Standard /24 reverse DNS zone:

69.131.37.in-addr.arpa

PTR record name inside that zone:

Full PTR owner name:

228.69.131.37.in-addr.arpa

PTR target:

ccvse.stc.com.bh.

Why This Happens

Reverse DNS zones are delegated based on control of the IP address block.

The organization that controls the IP address block is usually the ISP, hosting provider, or IP address provider.

UltraDNS can host the reverse DNS zone only when the applicable reverse DNS zone is delegated to UltraDNS name servers.

If the reverse DNS zone is not delegated to UltraDNS name servers, a PTR record created in UltraDNS is not authoritative for public reverse DNS lookups.

What You Should Do

Identify the organization that controls the IP address or IP block.
Contact your ISP, hosting provider, or IP address provider.
Ask whether they can create or update the PTR record for you, or whether they can delegate the applicable reverse DNS zone to UltraDNS name servers.
If they delegate the reverse DNS zone to UltraDNS, create the matching reverse DNS zone in UltraDNS.
Add the PTR record in the delegated reverse DNS zone.
Verify the result with:
```
dig -x <IP address>
```

Expected Outcome

If the reverse DNS zone is delegated to UltraDNS and the PTR record is created in the correct reverse DNS zone, a reverse lookup returns the configured hostname.

Example lookup:

dig -x 37.131.69.228

The response should return the hostname configured as the PTR target.

Check the Reverse DNS Delegation Path

To review the delegation path for the reverse DNS lookup, use:

dig -x 37.131.69.228 +trace

The trace output shows which name servers are authoritative for the reverse DNS zone.

Important Notes

Forward DNS and reverse DNS are delegated independently.
PTR records must be created in the applicable reverse DNS zone, not in the forward DNS zone.
UltraDNS hosting the forward DNS zone does not prove UltraDNS hosts reverse DNS for the related IP address.
UltraDNS can host reverse DNS only when the applicable reverse DNS zone is delegated to UltraDNS name servers.
Do not confuse the full PTR owner name with the reverse DNS zone name.
For 37.131.69.228, the full PTR owner name is 228.69.131.37.in-addr.arpa, but the standard /24 reverse DNS zone is 69.131.37.in-addr.arpa.
A customer may be correct to create the PTR record in the /24 reverse DNS zone if that zone is delegated to UltraDNS.

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