My custom domain works with GitHub Pages but I would like to understand how it actually works.
For this example I am not using my custom domain at all. My GitHub Pages repository does not contain a CNAME file.
E.g. Given a GitHub Pages repository without a CNAME file: example.github.io
DNS request for example.github.io resolves to 185.31.16.133
running the ping command for example.github.io also returns the same IP address: 185.31.16.133
When I open the website http://example.github.io in the browser, the browser show the contents of the actual website.
When I type an IP address 185.31.16.133 instead or make an HTTP GET request with a tool like Postman, all I see is a GitHub Pages 404 error.
Why can't I access my GitHub User page by an IP address directly? I thought that browsers replace hostname part of the URL with the IP address response of a DNS lookup, prior to making an HTTP request.
Best Answer
Yes, web browsers does a DNS lookup and uses that ip address for the connection. They also take the original host name and send it as part of the Host http header. This allows a web server to serve multiple web sites from the same ip address.
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