Suppose you type:

https://example.com

1. URL Parsing

• Browser breaks the URL into components:
  • Protocol → https
  • Domain name → example.com
  • Path → / (default root path if not specified)
  • Port → 443 (default for HTTPS, 80 for HTTP)

2. DNS Resolution

• The browser needs the IP address of example.com.
• Steps:
  1. Check browser cache → already resolved?
  2. Check OS cache → stored locally?
  3. Ask DNS resolver (from ISP or custom DNS like Google 8.8.8.8).
  4. If not cached, resolver queries root DNS → TLD (Top Level Domain) → authoritative DNS.
  5. Finally, gets IP (e.g., 93.184.216.34).

3. TCP Connection Setup

• Browser opens a TCP connection with the server:

  • Uses 3-way handshake:

    SYN → SYN/ACK → ACK

• Port 443 (for HTTPS) or 80 (for HTTP).

4. TLS/SSL Handshake (only if HTTPS)

• Secure channel is established:
  • Client and server exchange certificates.
  • Verify server’s certificate (issued by CA).
  • Negotiate encryption algorithms.
  • Generate session keys for encrypted communication.

5. Sending HTTP Request

• Browser sends a request to the server:

  GET / HTTP/1.1
  Host: example.com
  User-Agent: Chrome/119.0
  Accept: text/html
  Cookie: session=abc123
  

• This tells the server: “Give me the homepage of example.com.”