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What happens when you type a URL and press Enter?

You type a URL, hit Enter, and a whole chain reaction starts: DNS, TCP, TLS, HTTP, caching, and rendering all race to turn a name into a page. Here’s the mini-story of one webpage load. [31][6]

  • What happens when you click a URL - DNS Lookup, TCP Handshake & HTTP (With visuals)
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1) DNS lookup: the browser checks its own cache first, then the OS cache. If it still needs help, it asks a DNS resolver, which may do a recursive lookup until it finds the IP address. [6][8]

  • Diagram that shows the DNS multihomed name resolution queries for each server on each adapter.
  • Computer checks its DNS cache
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2) Connection setup + encryption: after DNS, the browser starts a TCP three-way handshake: SYN, SYN-ACK, ACK. If the site is HTTPS, TLS starts next, using a handshake to agree on secure communication and session keys. [7][14][15]

  • TCP 3 Way Handshake
  • TCP three way handshake explained with numbers
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3) Request and response: once the secure channel is ready, the browser sends an HTTP request. The server answers with HTML, and the browser starts parsing it while the response is still arriving. [6][21][31]

  • Steps involved in the parsing of HTML by a web browser
  • browser rendering works Data must be converted
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4) Caching and CDNs: page-load timing includes DNS, TCP, and SSL connect time, and rendering speed is shaped by latency. CDNs help by putting assets closer to users, while cached resources can still trigger validation checks. [21][3][30]

  • a screenshot of a computer
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5) Rendering on screen: the browser builds the DOM from HTML, the CSSOM from CSS, combines them into a render tree, then does layout and painting. That is the moment the page becomes visible and interactive. [22][24][32][31] Which step surprises you most? [33]

  • Understanding The Rendering Process
  • Calculating the layout and paint of a web page in a browser
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