IP Address Lookup

About IP Lookup

Give it a host name and it resolves every A and AAAA address, then does a reverse lookup on each. Give it an IP address and it goes straight to the reverse lookup. Both directions in one place, which is what you want when a log line has an address and you need to know who it belongs to.

Reverse records are also the part of mail configuration that quietly breaks delivery: many receivers reject or downgrade mail from a sending IP whose PTR record does not match its host name.

Each address is reported with what is publicly known about it: the AS number and operator announcing it, taken from the global routing table over DNS; the organisation, country and registered address from the regional registry's own record; and the PTR name it resolves back to. The registered address gets a maps link, and a sentence saying what it is worth — it is where the owner filed its paperwork, which for a large network is a head office on a different continent from the machine answering you.

Where it helps

• Handles a host name or a raw IP without you choosing a mode.
• Returns IPv4 and IPv6 addresses together, so a missing AAAA is obvious.
• Reverse DNS for every address, which is what mail providers check.
• The AS number, its operator and the prefix the address is announced in, read from the global routing table.
• Who the registry says the block belongs to — organisation, country and registered address — beside the address itself.
• Runs from the server, so results are independent of your local resolver.

Limits

• The city and region come from the registry's record for the block, which is the owner's filed address and not the machine's location — a network registered to one office answers from data centres everywhere.
• No true geolocation: placing a specific address needs a geo-IP database, which this does not ship.
• Absent reverse records are normal for most hosting; only mail servers really need them.
• Private and unresolvable addresses are rejected.
• A host behind a CDN resolves to edge nodes, which vary by location and tell you little about the origin.

Frequently asked questions

Why does one host return several addresses?

Round-robin DNS, a CDN, or a load balancer. Clients pick one, which is why intermittent faults often affect only some users.

Why is there no reverse record for my server?

PTR records are set by whoever owns the address block — your hosting provider — not in your own zone. Ask them to add it.

Can I find who owns an IP address?

Use WHOIS. This tool answers the naming question; registration and allocation live in the registry.

Why do I get an IPv6 address when my server has none?

Something in front of it does — usually a CDN or a proxy that publishes AAAA records of its own.

Related tools

• DNS Lookup — Resolve A, AAAA, MX, TXT, NS, CNAME, SOA and CAA records
• WHOIS — Registry records for a domain, an IP address or an AS number
• Ping (TCP) — Measure connection latency with repeated TCP probes
• Port Checker — Test whether TCP ports accept connections
• Nmap Port Scanner — Scan a host's common TCP ports, Nmap style, and see what each open service says it is
• What Is My IP — Your public address, and what a browser reveals about you

More Network & DNS tools

• DNS Lookup — Resolve A, AAAA, MX, TXT, NS, CNAME, SOA and CAA records
• Port Checker — Test whether TCP ports accept connections
• Nmap Port Scanner — Scan a host's common TCP ports, Nmap style, and see what each open service says it is
• Ping (TCP) — Measure connection latency with repeated TCP probes
• What Is My IP — Your public address, and what a browser reveals about you
• WHOIS — Registry records for a domain, an IP address or an AS number
• DNS Propagation Checker — The same name asked of resolvers worldwide, and of the zone's own servers
• Email Authentication Checker — SPF, DKIM, DMARC and MX for a domain, read together
• Email Header Analyzer — The delivery path, the authentication results, and what a forgery looks like
• DKIM Lookup — A domain's DKIM keys, for a selector or by trying the common ones, and whether each is worth anything
• DMARC Lookup — A domain's DMARC policy, and what it actually asks receivers to do
• Reverse DNS Lookup — The PTR record for an address, and whether it confirms itself
• IP Blacklist Checker — Whether an address is on the blocklists that actually stop mail
• Reverse IP Lookup — What an address says about itself: its name, its certificate, its network
• Traceroute — Every hop between this server and a host, with the time each one took
• Broadband Speed Test — Download, upload, latency and jitter, measured from this tab
• HTTP Headers — Grade a site's security headers from A+ to F, see every response header, and get the fix for your server
• Redirect Checker — Follow a URL's redirects hop by hop, and flag loops, downgrades and temporary redirects doing a permanent job
• IP Address Converter — Write an IPv4 or IPv6 address as an integer, hex, binary, expanded or mapped form, and see what kind it is
• MAC Address Lookup — Find the manufacturer behind a MAC address, and see what kind of address it is
• MAC to IP Converter — Build the IPv6 address a MAC forms with SLAAC, recover the MAC from one, or find a MAC's IP in an ARP table
• IP to MAC Lookup — Find the MAC address behind an IP: computed for multicast and EUI-64 addresses, or read from an ARP table
• DNSSEC Checker — Whether a domain's DNSSEC validates, and if not, whether it is the DS, a key, an algorithm or an expired signature