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Reverse IP Lookup

Which domains share an IP address.

How it works

Reverse IP lookup: what name and network sit behind an address

Give us an IPv4 or IPv6 address, or a domain and we will resolve it first, and we query the real reverse DNS (PTR) record by building the in-addr.arpa or ip6.arpa name and asking Cloudflare's resolver. We then fetch the network registration from the regional registry: owning organisation, network block, ASN and country, and check that the PTR name points back to the same IP (forward-confirmed reverse DNS), the test mail servers apply before accepting your email.

Results appear here after you click Reverse lookup.

How this works

1
Build the reverse name
The octets or nibbles are reversed into in-addr.arpa or ip6.arpa form and queried for a PTR record.
2
Look up the owner
The regional registry's RDAP service returns the organisation, network block, ASN and country for the address.
3
Confirm forward
Each PTR name is resolved back to see whether it points at the same IP, the check mail receivers use.

Frequently asked questions

What is a reverse IP lookup?: A forward lookup turns a name into an IP; a reverse lookup turns an IP back into a name using a PTR record in the special in-addr.arpa (IPv4) or ip6.arpa (IPv6) zone. The record is controlled by whoever owns the IP block, usually your hosting provider or ISP, not by your domain's DNS.
Why does my mail server need reverse DNS?: Gmail, Outlook and most receivers check that the sending IP has a PTR record and that the name resolves back to the same IP. Without it, mail is rejected or filed as spam. Set the PTR to your mail hostname, such as mail.example.com, and make sure that hostname has a matching A record.
How do I set or change a PTR record?: In your hosting or VPS control panel if the provider offers it (DigitalOcean, Hetzner, AWS and Linode do), otherwise by asking their support. You cannot set it at your domain registrar because the reverse zone belongs to the IP owner.
Can this tool list all websites on an IP?: No public DNS query can. That needs a passive-DNS archive built from years of observed lookups, which commercial services sell. This tool reports the authoritative PTR name and the network owner, which is what DNS actually knows about an address.
Why does a domain's IP show Cloudflare or Amazon as the owner?: Because the site is served through a proxy or cloud platform and the IP belongs to that provider. Thousands of unrelated sites may share the address, and the PTR will be the provider's generic name. The real origin server is hidden by design.

Every MailShrine domain includes WHOIS privacy, transfer lock, Anycast DNS with DNSSEC and two business mailboxes.