What happens when a URL is entered into a browser? How does DNS resolution work?

Entering a URL in a browser involves several sequential steps:

1. Parsing the URL — the browser breaks down the entered address into parts: protocol (http/https), domain name, path, parameters.

2. DNS resolution — the browser needs to find out the IP address of the server by the domain name:

   • First, it checks the local DNS cache.
   • If not found, a request is sent to the configured DNS server (usually the provider's).
   • DNS servers recursively search for the IP, starting from root servers, then top-level domain (TLD) servers, and finally authoritative DNS servers for the domain.
   • The obtained IP is returned to the browser.

3. Establishing a TCP connection with the server using the obtained IP and port (usually 80 for HTTP or 443 for HTTPS).

4. TLS handshake (if HTTPS) — a secure connection is established.

5. Sending an HTTP request — the browser sends a request to the server.

6. Receiving a response — the server returns HTML, CSS, JS, and other resources.

7. Rendering the page — the browser processes the received data and displays the page.

DNS resolution is the process of converting a domain name into an IP address, necessary for establishing a network connection. It is based on a hierarchical system of DNS servers and caching to speed up repeated requests.