What happens, step by step, when you type a URL into a browser and press enter?
What they are really testing: The classic end-to-end test. They want to see if you can trace a request across DNS, TCP, TLS, and HTTP layers in order, and how deep your mental model goes.
A real interview question
What happens, step by step, when you type a URL into a browser and press enter?
What most people say
drag me
“The browser sends a request to the server and the server sends back the web page.”
It collapses the whole stack into one step. It shows no awareness of DNS, the TCP handshake, or TLS, which is exactly what the question is probing.
The follow-ups they ask next
Where can caching short-circuit these steps?
DNS results cache by TTL; the browser and CDN cache responses; even TLS sessions can be resumed. Each cache removes a round trip.
The page loads but is slow. How do you find which step is the bottleneck?
Browser devtools waterfall: separate DNS time, connect/TLS time, time-to-first-byte (server), and download time. The phase that dominates tells you where to look.
What the interviewer is listening for
- Names DNS, TCP, TLS, HTTP in order
- Mentions caching/CDN
- Can go deeper on any layer when pushed
What sinks the answer
- Skips DNS or the handshake entirely
- No notion of layers
- Cannot expand beyond "request and response"
If you genuinely do not know
Say this instead of freezing. Reasoning out loud from what you do know beats silence every single time, and a good interviewer is listening for exactly that.
“First [DNS turns the hostname into an IP, via cache then a resolver]. Then [a TCP handshake opens the connection on port 443]. For https, [a TLS handshake validates the cert and agrees a session key]. Then [the HTTP GET goes out, often through a CDN/load balancer] and [the browser renders the HTML plus CSS/JS/images]. I can go deeper at [any layer].”
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