What Happens When You Type a URL Into Your Browser?

The diagram above illustrates the steps.

• Bob enters a URL into the browser and hits Enter. In this example, the URL is composed of 4 parts:

  • scheme - http://. This tells the browser to send a connection to the server using HTTP.
  • domain - example.com. This is the domain name of the site.
  • path - product/electric. It is the path on the server to the requested resource: phone.
  • resource - phone. It is the name of the resource Bob wants to visit.

• The browser looks up the IP address for the domain with a domain name system (DNS) lookup. To make the lookup process fast, data is cached at different layers: browser cache, OS cache, local network cache, and ISP cache.

  • If the IP address cannot be found at any of the caches, the browser goes to DNS servers to do a recursive DNS lookup until the IP address is found (this will be covered in another post).

• Now that we have the IP address of the server, the browser establishes a TCP connection with the server.

• The browser sends an HTTP request to the server. The request looks like this:

  𝘎𝘌𝘛 /𝘱𝘩𝘰𝘯𝘦 𝘏𝘛𝘛𝘗/1.1
  𝘏𝘰𝘴𝘵: 𝘦𝘹𝘢𝘮𝘱𝘭𝘦.𝘤𝘰𝘮

• The server processes the request and sends back the response. For a successful response (the status code is 200). The HTML response might look like this:

  𝘏𝘛𝘛𝘗/1.1 200 𝘖𝘒
  𝘋𝘢𝘵𝘦: 𝘚𝘶𝘯, 30 𝘑𝘢𝘯 2022 00:01:01 𝘎𝘔𝘛
  𝘚𝘦𝘳𝘷𝘦𝘳: 𝘈𝘱𝘢𝘤𝘩𝘦
  𝘊𝘰𝘯𝘵𝘦𝘯𝘵-𝘛𝘺𝘱𝘦: 𝘵𝘦𝘹𝘵/𝘩𝘵𝘮𝘭; 𝘤𝘩𝘢𝘳𝘴𝘦𝘵=𝘶𝘵𝘧-8
  
  <**!𝘋𝘖𝘊𝘛𝘠𝘗𝘌** 𝘩𝘵𝘮𝘭>
  <**𝘩𝘵𝘮𝘭** 𝘭𝘢𝘯𝘨="𝘦𝘯">
  𝘏𝘦𝘭𝘭𝘰 𝘸𝘰𝘳𝘭𝘥
  </**𝘩𝘵𝘮𝘭**\>

• The browser renders the HTML content.