Top 4 Dns Interview Questions
Browse 4 real-world technical and behavioral interview questions about Dns. Review scenarios, edge cases, and architectural best practices.
Your application cannot reach a service that should be up. Walk me through diagnosing it from the shell.
Work up the layers and let each command eliminate a class of cause: resolve the name, check the route, see whether anything is listening, then decide from the failure mode whether packets are being refused, silently dropped, or answered by something that never replies.
You are about to change the address a hostname points to. What does the TTL actually promise you, and why do clients keep reaching the old address anyway?
A TTL is an upper bound on how long a resolver may cache a record, not a promise about when clients will notice a change. Lowering it only takes effect after one old TTL has elapsed, negative answers are cached under a different rule, and pooled connections keep using an address they resolved hours ago.
Walk me through everything that happens when you type a URL into the browser and press enter.
The browser checks its caches, resolves the hostname through browser, OS and resolver caches, opens a TCP connection, completes a TLS handshake, sends the request, then parses the streamed response. QUIC fuses transport and crypto setup into one round trip and stops one lost packet stalling every stream.
The tooling you would use to fix a network outage runs over the network that is down. How do you break that circularity before it costs you a day?
Separate the layers that can fail together: routing reachability, name resolution, identity and physical access. Then build an access path that shares none of them, keep controls failing static rather than closed, and rehearse the emergency path often enough that it is known to work.