IP Lookup

What it does

IP Lookup takes any public IPv4 or IPv6 address and returns the data registered against it: the autonomous system number (ASN) and the network operator that announces it, the regional internet registry (ARIN, RIPE, APNIC, LACNIC, or AFRINIC), approximate geolocation, abuse contact, and the reverse DNS PTR record. It's the canonical way to identify who owns and operates a given address on the internet. To look up your own public IP, use What is My IP; to verify mail-server reputation for an IP, run it through IP Blacklist Check.

When to use it

• Investigating a suspicious IP from your firewall or web server logs to determine whether it belongs to a known cloud provider, residential ISP, or hosting platform. Cross-check reputation with IP Blacklist Check.
• Identifying the abuse contact for a network so you can report scraping, brute-force attempts, or spam.
• Confirming that an IP claimed to be your customer's office really belongs to their corporate ASN before whitelisting it.
• Tracing the upstream provider of an IP that's failing to reach your service to determine where to route a peering request. If latency is the symptom, also check Speed Test.
• Verifying that a vendor's "static IP" is actually inside the ASN they say it is — and not a transient cloud or CDN address.

How to read the results

The ASN tells you which network is announcing the address via BGP — large ASNs like Google's AS15169 or Cloudflare's AS13335 indicate cloud infrastructure, while ASNs registered to consumer ISPs indicate residential traffic. The CIDR block shows the size of the allocation containing the IP. The registry (RIR) determines which database holds the authoritative WHOIS record — for domain WHOIS rather than IP WHOIS, see WHOIS Lookup. Abuse contacts are mandatory and are the correct address for reporting malicious activity. To pivot from an IP to its hostname, use Reverse DNS.

Common mistakes

• Treating the registered organization name as the actual user — a single ASN can host millions of customers, and the name belongs to the network operator, not the end user.
• Confusing the IP's registered country with the physical server location; IPs from one regional registry can be routed and used anywhere on the planet.
• Reading a missing PTR record as evidence of malice — many legitimate networks simply don't publish reverse DNS for client subnets. Confirm with Reverse DNS.
• Assuming the abuse contact will act quickly; large ISPs aggregate reports and may take days to respond, so always include logs with timestamps in UTC.