# Journey of a URL

> Step-by-step technical breakdown of web requests and browser page rendering

This educational reference outlines the technical lifecycle that occurs when entering a URL into a web browser. It details DNS lookup hierarchies, the TCP three-way handshake, HTTP request and response cycles, and browser rendering pipeline stages. It is useful as a study guide for software engineering and web development technical interviews.

## How it works

The Journey of a URL involves 4 primary stages:

1. DNS Lookup (Resolving domain name to IP):
2. Cache check order: Browser Cache -\> Operating System Cache -\> Router Cache -\> ISP Cache.
3. If cache miss: Query Root Domain Name Server -\> 2nd Level Domain Name Server -\> 3rd Level Domain Name Server to resolve IP address.
4. Initiate TCP Connection (Three-Way Handshake):
5. Step 1: Client sends SYN packet to Server.
6. Step 2: Server responds with SYN-ACK packet to Client.
7. Step 3: Client sends ACK packet back to Server.
8. HTTP Request & Server Response:
9. Client sends HTTP Request (e.g., GET /mypage.com).
10. Server returns Server Response with status code:
11. 1xx: Information Message
12. 2xx: Success
13. 3xx: Redirects
14. 4xx: Client Errors
15. 5xx: Server Errors
16. Browser Rendering Pipeline:
17. Receives HTML + CSS + JS files.
18. HTML Document -\> Tokenizer -\> DOM Tree.
19. CSS Stylesheet -\> Tokenizer -\> CSSOM Tree.
20. JavaScript is evaluated and can manipulate DOM/CSSOM trees.
21. DOM Tree + CSSOM Tree -\> Render Tree -\> Layout calculation -\> Painting -\> Web Page Successfully Loaded.

## What it is for

- Prepare for web development and software engineering technical interview questions
- Understand the end-to-end lifecycle of browser network requests and DOM rendering
- Debug web performance bottlenecks across network and rendering phases

## Key points

- DNS lookup caching sequence checking browser, OS, router, and ISP caches
- Hierarchical DNS query resolution through root, 2nd level, and 3rd level servers
- TCP three-way handshake connection sequence (SYN, SYN-ACK, ACK)
- HTTP client-server request and response cycle with standard status code ranges
- Parsing HTML and CSS into DOM and CSSOM trees
- Render tree construction combining DOM and CSSOM for layout and paint execution

## Pricing

Free

## Details

- Type: Tip
- Category: [Learning](https://xiry.app/topics/learning.md)
- Open source: no
- Platforms: other
- For: Web developers, software engineering students, and interview candidates
- Tags: networking, webdev, dns, browsers, interview prep, frontend

## Why it was saved

- [@codewithbrij, 6 September 2023](https://www.instagram.com/reel/Cw2ygzLvA4A/): Provides a clear, concise visual reference for web networking and browser rendering concepts frequently asked in software engineering and web development interviews.

## Related

- [Epic Growth Community](https://xiry.app/resources/epic-growth-community): Professional community and video case study library for product growth and marketing (Website, Paid)

Updated 3 October 2026. Page: https://xiry.app/resources/journey-of-a-url

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