How we find out who hosts a website

We ask public DNS resolvers (Cloudflare's 1.1.1.1 and Google's 8.8.8.8) for the hostname's IPv4 and IPv6 addresses. If a bare domain such as example.com has no address of its own, we use www.example.com instead.

A name with no DNS records at all doesn't exist. A name that exists but has no addresses isn't hosting a website. We say which of the two it is, rather than reporting an error.

Every IP address on the internet belongs to a network, identified by an autonomous system number (ASN) and run by an organisation such as Amazon, Google or a hosting company. We look each address up in IPinfo's free IP database, refreshed every week, which gives the network, its owner and the country where the address is located.

The network that owns the address is usually the hosting provider. For example, 8.8.8.8 belongs to Google. Large organisations often run several ASNs, so we group them by owner: see the networks behind popular websites.

Most large websites don't let visitors connect to their own servers directly. They sit behind a content delivery network (CDN) such as Cloudflare, Akamai, Fastly or Amazon CloudFront. Visitors connect to the CDN, and the CDN fetches pages from the website's real servers, known as the origin.

That origin is deliberately hidden, so any DNS or IP lookup shows the CDN rather than the company hosting the website behind it. When we detect a CDN, we say so instead of presenting it as the host. For example, bbc.com is served through Fastly.

We recognise a CDN in three ways:

• the www hostname points (by CNAME) to a CDN's domain, such as bbc.map.fastly.net;
• the address is in Amazon CloudFront's published address ranges;
• the address belongs to a network that only runs a CDN or protective proxy, such as Cloudflare.

The same CNAME check spots hosting platforms such as Shopify, Vercel, Netlify, WP Engine and Squarespace, which host the website themselves.

Websites often use different companies for hosting, DNS and email. The DNS provider comes from the domain's nameserver (NS) records, and the email provider from its mail server (MX) records. Some mail servers belong to security gateways such as Proofpoint or Mimecast, which filter mail before passing it on; we label those as gateways.

The country is where IPinfo locates the address we reached. Large websites and CDNs run servers in many countries and send each visitor to a nearby one, either by giving different addresses to different parts of the world or by announcing the same address from many places (anycast). So the country you'd reach can differ from ours: our checks run from Europe.

Pages for popular websites show the result of our last scheduled check, with its date, and a history once the hosting changes. Any page can run a live check, and lookups from the search box are always live. The IP database is refreshed weekly.