What Is My IP Address? What Websites Can See

Public and private addresses

Inside a home or office, devices get private addresses such as 192.168.1.20 from ranges set aside in RFC 1918. Thousands of networks reuse the same private ranges, so internet routers will not carry traffic to them. Your router holds a public address, assigned by your provider, and uses network address translation (NAT, described in RFC 3022) to send every device’s traffic out under that one address:

This is why every phone, laptop and television in a house shows the same public IPv4 address, and why a website cannot tell them apart by address alone. NAT and Private IP Address Ranges covers the ranges and the translation table in more detail.

Many providers now add a second layer, carrier-grade NAT. Your router gets an address from the shared range 100.64.0.0/10 (RFC 6598), and the provider translates again before traffic reaches the internet. When that happens, the public address you see is shared with other customers at the same moment, and you cannot accept incoming connections on it. If the WAN address on your router’s status page differs from the address a lookup shows, something else is translating your traffic: a second router of your own, a VPN or proxy, a multi-WAN setup, or carrier-grade NAT. A WAN address inside 100.64.0.0/10 is a strong sign of carrier-grade NAT, and your provider can confirm it.

Why you may have two addresses

IPv4 addresses are 32 bits long (RFC 791), which allows about 4.3 billion of them, and the free pools ran out years ago. IPv6 addresses are 128 bits (RFC 4291), enough for every device to have its own globally reachable address. Most networks run both at once, which is called dual stack.

When a site supports both, browsers use the Happy Eyeballs method from RFC 8305: they try IPv6 first and start an IPv4 attempt if IPv6 has not connected within a short delay, 250 milliseconds by default. So a site that supports IPv6 usually records your IPv6 address, and an IPv4-only site records your IPv4 address. Both identify the same connection.

Because an IPv6 address can belong to one device, operating systems use temporary addresses for outgoing connections (RFC 8981). They change regularly, so the IPv6 address you see today may differ tomorrow even though the network part stays the same. IPv4 vs IPv6 and AAAA Records explains how the two families appear in DNS.

Provider, network and ASN

Addresses are handed out in blocks. IANA allocates large blocks to the five regional internet registries (ARIN, RIPE NCC, APNIC, LACNIC and AFRINIC), which assign them to providers and organizations. Each network announces its blocks to the rest of the internet with BGP under an autonomous system number, or ASN (RFC 1930). That makes the ASN and its organization name a reliable way to tell which network an address sits on: your home broadband provider, a mobile carrier, a company, a cloud host or a VPN service.

The routed address block, or prefix, is the most specific range announced for your address, such as 203.0.113.0/24. BGP Basics: How Internet Routing Works explains how those announcements spread.

Some addresses also have a reverse DNS name, published by the block’s owner as a PTR record under in-addr.arpa or ip6.arpa (RFC 3596). Providers often encode the customer area or connection type in it. It is optional and can say anything the owner likes; see Reverse DNS and PTR Records.

How accurate IP location is

No part of an IP address encodes a location. Geolocation services build databases that map address blocks to places, using registry records, measurements, and feeds that providers publish themselves in the geofeed format of RFC 8805. The results are reliable for the country, usually close for the region, and often tens of kilometres off for the city. The map coordinates are the centre of the estimated area, not your home.

Location is most likely to be wrong when:

• You use a mobile network. Carriers often route traffic through a few large gateways, so a phone can appear hundreds of kilometres away.
• You use a VPN, proxy or relay service. Sites see the relay’s address and location by design.
• Your provider recently moved the block. Databases lag until the provider’s geofeed or the database vendor catches up.
• You use a corporate network. Traffic may leave for the internet from head office or a security service in another city.

A mismatch between the time zone your browser reports and the one linked to your IP address is a common sign of a VPN or a distant gateway. It is also one of the ways websites guess that a VPN is in use.

What websites can and cannot learn

A website you visit can record your public address, the provider and rough location linked to it, and what your browser sends with every request: its name and version, operating system and preferred language. Servers keep this in access logs, and many sites use it to choose a language, block abuse or estimate a region for content licensing.

A website cannot learn your name, email address or street address from your IP address, see your device’s private address, or list the other devices on your network. Linking an address to a subscriber needs your provider’s own records, which is why server operators are advised to log the source port and an accurate timestamp as well (RFC 6302): under carrier-grade NAT, the address alone may match many customers.

How DNS Panopticon helps

What Is My IP reads everything from the request your browser makes to it. Cloudflare, which runs this site’s edge, passes on the connecting address and its own data about it, as documented in the Workers request reference: the ASN and organization, the city, region, country and time zone, the data center that answered, and the connection’s protocol and round-trip time. Two DNS lookups add the reverse DNS name and the routed prefix, the latter from Team Cymru’s IP-to-ASN service.

A page load only travels over one address family, so the tool also asks icanhazip.com, a service now run by Cloudflare, for your address once over IPv4 and once over IPv6. Provider and location details describe the address the page itself loaded over. Nothing is stored.