What Happens After You Type a URL? A Step‑by‑Step Animation

Step 1: URL to IP address

When a user enters a URL (e.g., www.linuxyz.cn) and presses Enter, the browser attempts to resolve the hostname to an IP address. It first checks several caches in order: browser cache, operating‑system cache, local DNS cache, and ISP cache. If none contain the mapping, the browser sends a query to a DNS resolver.

Step 2: Recursive DNS lookup

If the resolver does not have the answer, it performs a recursive DNS lookup, traversing the DNS hierarchy (root, TLD, authoritative name servers) until the authoritative server for the domain returns the IP address.

Step 3: TCP connection and TLS handshake

With the IP address, the browser establishes a TCP connection using the three‑way handshake. Immediately after, it initiates a TLS (HTTPS) handshake: the server presents its X.509 certificate containing the public key, the client encrypts a freshly generated session key with that public key, the server decrypts it with its private key, and both sides derive the symmetric session key used for encrypted application data.

Step 4: HTTP request, response, and rendering

The browser sends an HTTP request over the established TLS channel. A successful response carries status code 200 and includes HTML, CSS, and JavaScript resources. The browser parses the HTML to build the DOM tree, parses the CSS to build the CSSOM tree, merges them into a render tree, performs layout, and paints the page for the user.

Code example

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