Interview Q&A / Computer Networks
Computer Networks interview questions
What happens when you open a website, TCP vs UDP, DNS and HTTP.
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- Can UDP datagrams arrive out of order, duplicated, or not at all?
Yes to all three. UDP makes no promises about order, duplicates, or delivery. Each datagram is independent and can take a different route, so the application must tolerate or handle these cases.
BeginnerQuick answer1 min read - How does TCP detect and recover from a lost packet?
The sender retransmits when its timer expires without an ACK, or sooner if it receives three duplicate ACKs, which signal that later segments arrived but one is missing. That second path is called fast retransmit.
IntermediateQuick answer1 min read - UDP is unreliable. How can an application still get reliable delivery over it?
The application adds what it needs on top: sequence numbers to order and detect gaps, acknowledgements and retransmission for missing data, and timers. QUIC, used by HTTP/3, does exactly this over UDP, along with congestion control and encryption.
AdvancedQuick answer1 min read