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PTR Record Lookup (reverse DNS)

Perform reverse DNS resolution for your IP address

Email deliverability issues? Check that your IP address has a valid PTR record consistent with your DNS configuration.

In iterative trace mode, the resolver is ignored.
Query multiple public resolvers to compare answers.

Reverse resolution

Discover which hostname is associated with an IP address. Essential for email and network logging.

Multi-resolver

Compare responses from Google, Cloudflare, and Quad9 to detect propagation issues.

Forward-reverse consistency

Verify that the name returned by PTR resolves back to the original IP address via A/AAAA record.

IPv4 and IPv6

Full support for in-addr.arpa (IPv4) and ip6.arpa (IPv6) zones for all your addresses.

Free and unlimited

Test as many addresses as needed. No signup required.

How to use the DNS lookup engine options effectively

What is the iterative trace?

The trace performs resolution step by step. The resolver first queries the root servers, then the TLD (.com, .fr, .eu), and then the authoritative servers of the target zone. At each step, the page shows the queried server, the answer, the RCODE, and the latency.

  1. 1. Root

    Discovery of the TLD servers for the requested name.

  2. 2. TLD

    Reference to the zone's NS (delegation).

  3. 3. Authoritative

    Final answer (or error) with TTL and latency.

What is it for?

  • Compare answers across resolvers and regions
  • Detect a hot cache, an overly long TTL, or an incomplete delegation
  • Explain a latency difference or an unexpected RCODE

Tip: keep the trace disabled for quick checks; enable it when investigating or preparing a ticket/post‑mortem.

What is the classic trace?

The classic trace queries only the selected resolver (UDP or DoH) and displays the answer as it is perceived from that network vantage point. You get the RCODE, the response sections, and the latency for the client → resolver leg.

  1. 1. Chosen resolver

    Uses the preset or custom configuration to run the query exactly like your service would.

  2. 2. Protocol preserved

    Respects the selected transport (UDP, TCP, or DoH) so you reproduce the real behaviour.

  3. 3. Detailed answer

    Shows the question, answer, and authority/additional sections when present, together with TTL and useful metadata.

Why use it?

  • Check the view of a specific resolver before suspecting delegation issues
  • Confirm cached values and the impact of a TTL or a flush
  • Document a resolution exactly as a client or microservice sees it

Tip: keep the iterative trace option turned off when auditing a given resolver; enable it afterwards to compare with the root → TLD → authoritative path.

How does the propagation test work?

The test queries a set of public resolvers (Google, Cloudflare, Quad9, OpenDNS, ISPs…) in parallel and groups the answers by content and RCODE. You instantly see who already picked up the update.

  1. 1. Multi-point resolvers

    Enables the propagation presets to question several actors spread around the world.

  2. 2. Automatic comparison

    Groups identical answers and highlights divergences or resolver-specific errors.

  3. 3. Actionable summary

    Provides a clear recap, the resolver list, their latencies, and each group's status.

When to use it?

  • Track how a DNS change propagates worldwide
  • Spot stale caches and decide on a targeted flush
  • Share a propagation snapshot in a ticket or post-mortem

Tip: while the propagation test is active, the resolver selector is frozen. Disable the mode to return to single-resolver diagnostics.

What is a PTR record?

A PTR (Pointer) record performs reverse DNS resolution: it maps an IP address to a hostname. This is the opposite operation of A (IPv4) and AAAA (IPv6) records.

PTR record structure:

FieldDescriptionExample
NameReversed address + arpa zone10.113.0.203.in-addr.arpa.
TypeAlways PTRPTR
TargetAssociated hostnamemail.captaindns.com.
TTLCache duration in seconds3600

PTR record examples

IPv4 (in-addr.arpa)

Address 203.0.113.10 written in reverse:

10.113.0.203.in-addr.arpa.  3600  IN  PTR  mail.captaindns.com.

IPv6 (ip6.arpa)

Address 2001:db8::10 with each hex nibble reversed:

0.1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.  3600  IN  PTR  host.captaindns.com.

Forward-confirmed reverse DNS (FCrDNS)

Forward-reverse consistency is essential:

  1. PTR: IP 203.0.113.10 returns mail.captaindns.com
  2. A: Name mail.captaindns.com resolves to 203.0.113.10

This consistency is required by:

  • Email servers (anti-spam)
  • Security services
  • Logging systems

Important rules

Correct configuration

RuleExplanation
One PTR per IPAvoid multiple PTRs for the same address
FCrDNS consistencyName must resolve back to original IP
Meaningful nameUse a name that identifies the service

Email best practices

PracticeWhy
PTR requiredMany servers reject without PTR
Match HELOName should match SMTP HELO
No generic namesAvoid names like host-203-0-113-10.isp.com

Common issues

Missing PTR (NXDOMAIN)

No PTR record exists for the address.

  1. Contact your IP address provider
  2. Request PTR creation with desired name
  3. Verify after propagation

FCrDNS inconsistency

Returned name doesn't resolve to original IP.

  1. Check the A/AAAA record for the name
  2. Correct if IP doesn't match
  3. Wait for propagation

Emails rejected for PTR

Destination servers reject your emails.

  1. Verify PTR exists
  2. Ensure FCrDNS consistency
  3. Match SMTP HELO name

Command line verification

Linux/Mac

Simple reverse lookup:

dig -x 203.0.113.10

Or with full notation:

dig PTR 10.113.0.203.in-addr.arpa

Windows

nslookup 203.0.113.10

PTR management

Who manages the reverse zone?

SituationManager
Dedicated serverThe host (via their interface or support)
Cloud (AWS, GCP, Azure)The cloud provider (via their console)
Own IP blockYou (if you have delegation)
Residential IPThe ISP (rarely modifiable)
ToolPurpose
A Record LookupCheck forward IPv4 resolution
AAAA Record LookupCheck forward IPv6 resolution
Email TestCheck complete email configuration

Useful resources