Find your own public IP address, see roughly where any IP is and which network it belongs to, check whether a mail server's IP is blocklisted, and plan address ranges with a subnet calculator.
| I want to… | Use |
|---|---|
| Find the public IP address my connection uses | What's My IP Address? |
| See roughly where an IP address is and which ISP it belongs to | IP Address Lookup |
| Find which organisation an IP range is registered to | WHOIS Lookup |
| Find the hostname behind an IP | Reverse DNS Lookup |
| Find out why a mail server's messages are being rejected | IP Blacklist Check, then Email tools |
| Work out a network range, netmask or number of usable hosts | Subnet Calculator |
A public IP address is reachable on the internet and is what websites see when you connect. A private address is only used inside a local network; your router translates it to a public address (NAT). These ranges are reserved for private or shared use and never appear as a public address:
| Range | Used for |
|---|---|
10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 | Private IPv4 networks (RFC 1918): home, office and cloud networks |
100.64.0.0/10 | Carrier-grade NAT (RFC 6598): shared by ISP customers behind the provider's NAT |
127.0.0.0/8, ::1 | Loopback: the machine itself |
169.254.0.0/16, fe80::/10 | Link-local: assigned automatically when no DHCP server answers |
fc00::/7 | IPv6 unique local addresses, the IPv6 equivalent of private ranges |
IPv4 addresses are 32 bits, written as four decimal numbers (203.0.113.7). IPv6 addresses are 128 bits, written as eight groups of hexadecimal digits with runs of zeros shortened to :: (2001:db8::7). Many connections have both; which one a website sees depends on whether the site and your network both support IPv6.
IP location comes from databases that map address ranges to places, not from GPS. The country is usually right; the city is often the location of the ISP's equipment rather than the user, and can be off by a long way. VPNs, mobile networks and corporate proxies show the location of their exit point. Treat IP location as approximate.