All 41 questions

  1. How do TCP and UDP differ, and when would you choose each for an application?

    Asked in 8 of 337 interviews · last asked Oct 12 · Concept · Junior

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    TCP is connection-oriented and provides reliable, ordered delivery of bytes. UDP sends separate packets without guaranteeing delivery or order. Choose TCP when complete, ordered data matters, such as file transfers. Choose UDP when late data is less useful than missing data, such as live calls, or when the application handles reliability itself.

    • TCP retransmits lost data and includes flow control and congestion control.
    • TCP is a byte stream; UDP preserves message boundaries.
    • UDP has less protocol overhead, but it is not always faster.
    • UDP applications must handle loss and reordering if these matter.

    What the interviewer checks: The interviewer checks whether you can match delivery guarantees and delay needs to an application's requirements.

    Other ways it was asked
    • “What is the difference between TCP and UDP?”
    • “Can you tell me the difference between TCP and UDP?”
    • “What is the difference between UDP and TCP?”

  2. How does the TCP three-way handshake work, including for HTTP/1 and HTTP/2 connections?

    Asked in 6 of 337 interviews · last asked Oct 16 · Concept · Junior

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    The client sends SYN, the server replies with SYN-ACK, and the client sends ACK. This establishes a TCP connection and exchanges starting sequence numbers for both directions. HTTP/1 and HTTP/2 use this handshake when opening a new TCP connection. They can reuse that connection for multiple requests.

    • SYN-ACK acknowledges the client's SYN; the final ACK acknowledges the server's SYN.
    • For HTTPS, TLS setup follows TCP setup, before normal HTTP traffic.
    • HTTP/2 can carry multiple active request streams over one TCP connection.
    • Repeated SYN packets without SYN-ACK suggest packet loss, filtering, or an unreachable server; RST can indicate connection refusal.

    What the interviewer checks: The interviewer checks whether you understand TCP setup, packet traces, and how HTTP and TLS use TCP.

    Other ways it was asked
    • “What is the TCP three-way handshake?”
    • “Can you explain the TCP three-way handshake?”
    • “What happens during the TCP three-way handshake?”

  3. What is TCP?

    Asked in 5 of 337 interviews · last asked Sep 9 · Concept · Junior

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    TCP stands for Transmission Control Protocol. It is a connection-oriented transport-layer protocol that provides reliable, ordered delivery of a byte stream between applications. It detects lost data and retransmits it, while using flow control and congestion control to manage transmission.

    • TCP establishes a connection, usually with a three-way handshake.
    • Sequence numbers and acknowledgments support ordered delivery and retransmission.
    • Flow control protects the receiver; congestion control limits pressure on the network.
    • TCP carries a byte stream, so it does not preserve message boundaries.

    What the interviewer checks: The interviewer is checking whether you understand TCP’s role, reliability, connection setup, and basic traffic controls.

    Other ways it was asked
    • “What does TCP mean?”
    • “What is the TCP protocol?”
    • “What does TCP stand for, and what is it?”

  4. What is UDP?

    Asked in 4 of 337 interviews · last asked Jul 29 · Concept · Junior

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    UDP (User Datagram Protocol) is a connectionless transport-layer protocol that sends data as separate packets called datagrams. It does not guarantee delivery, order, or protection against duplicates. Its low overhead suits uses such as DNS queries, live audio and video, and online games.

    • No connection setup is required before sending data.
    • UDP preserves message boundaries but does not retransmit lost packets.
    • Applications must handle missing or out-of-order data if needed.
    • DNS commonly uses UDP, but it also uses TCP.

    What the interviewer checks: The interviewer is checking whether you understand UDP’s delivery limits and why applications choose it over TCP.

    Other ways it was asked
    • “What can you tell me about UDP?”
    • “What is UDP, and what type of protocol is it?”
    • “What are some applications that use UDP?”

  5. What is a port?

    Asked in 3 of 337 interviews · last asked Sep 19 · Concept · Junior

    Other ways it was asked
    • “What is a port number?”

  6. What is the difference between CRC and checksum?

    Asked in 2 of 337 interviews · last asked Mar 28 · Concept · Junior

  7. What are the various types of ARQ protocols?

    Asked in 2 of 337 interviews · last asked Mar 28 · Concept · Junior

  8. What is the maximum segment size (MSS) in TCP?

    Asked once · last asked Feb 24 · Concept · Junior

  9. Why does TCP behave differently from UDP?

    Asked once · last asked Feb 3 · Concept · Junior

  10. How does TCP establish a connection?

    Asked once · last asked Feb 24 · Concept · Junior

  11. How does TCP terminate a connection?

    Asked once · last asked Feb 24 · Concept · Junior

  12. In a Wireshark capture, what does a TCP window-zero notification mean?

    Asked once · last asked Mar 20 · Concept · Mid-level

  13. What does the window size mean in a TCP packet?

    Asked once · last asked Mar 20 · Concept · Junior

  14. Which device sets the window size on a TCP connection?

    Asked once · last asked Mar 20 · Concept · Junior

  15. Which ports does PSM use to connect to target systems over RDP and SSH?

    Asked once · last asked May 25 · Concept · Mid-level

  16. How can a sliding-window mechanism be implemented with Axway Secure Transport, and is it built in or custom-developed?

    Asked once · last asked Jun 18 · Concept · Senior

  17. What happens if the final acknowledgment in the three-way handshake gets lost?

    Asked once · last asked Jun 20 · Scenario · Mid-level

  18. When DNS works over VPN but internal apps still fail, how would you verify whether MTU/MSS issues are causing TCP blackholing, and what symptoms would you expect?

    Asked once · last asked Sep 2 · Scenario · Senior

  19. Identify the service protocol that commonly runs on port 80, port 443, port 53, and port 3389, and briefly describe what each service is used for.

    Asked once · last asked Sep 29 · Concept · Junior

  20. How would you explain TCP and UDP, including TCP flags and when you would use one protocol over the other?

    Asked once · last asked Oct 7 · Concept · Junior

    Other ways it was asked
    • “How would you explain TCP and UDP, including their flags and why one would be used over the other?”

  21. What would a packet capture full of reset flags over about five minutes probably indicate?

    Asked once · last asked Oct 8 · Scenario · Mid-level

  22. Can a TCP zero-window condition originate on the server rather than the client?

    Asked once · last asked Mar 20 · Concept · Mid-level

    Other ways it was asked
    • “What server-side conditions can cause a TCP zero-window notification?”

  23. What can you tell me about the transport protocols?

    Asked once · last asked Feb 24 · Concept · Junior

  24. What application uses TCP port 3389?

    Asked once · last asked Mar 6 · Concept · Junior

    Other ways it was asked
    • “What applications use TCP ports 1521 and 1433?”

  25. What application uses port 443?

    Asked once · last asked Mar 6 · Concept · Junior

  26. Is a TCP window-zero condition always caused by the user’s device?

    Asked once · last asked Mar 20 · Concept · Mid-level

  27. What do TCP and UDP stand for?

    Asked once · last asked Mar 27 · Concept · Junior

  28. What is selective repeat ARQ?

    Asked once · last asked Mar 28 · Concept · Junior

  29. Can you technically explain what the UDP protocol is?

    Asked once · last asked Mar 28 · Concept · Junior

  30. What connectionless protocols are available?

    Asked once · last asked Mar 28 · Concept · Junior

  31. What is flow control in TCP?

    Asked once · last asked Mar 28 · Concept · Junior

  32. What is port 80 used for?

    Asked once · last asked Apr 16 · Concept · Junior

  33. What is port 443 used for?

    Asked once · last asked Apr 16 · Concept · Junior

  34. What is port 25 used for?

    Asked once · last asked Apr 16 · Concept · Junior

  35. What is a TCP port number?

    Asked once · last asked May 13 · Concept · Junior

    Other ways it was asked
    • “What is the port number for TCP?”

  36. Explain the TCP sliding window.

    Asked once · last asked Jul 16 · Concept · Junior

  37. What layer do TCP and UDP operate at, and what are the primary differences between them?

    Asked once · last asked Aug 4 · Concept · Junior

  38. What is required for TCP to establish a session?

    Asked once · last asked Aug 4 · Concept · Junior

  39. What is a network port, and what does a port number identify?

    Asked once · last asked Sep 19 · Concept · Junior

  40. Which port does HTTP use?

    Asked once · last asked Oct 13 · Concept · Junior

  41. What is the port number for SMTP?

    Asked once · last asked Oct 19 · Concept · Junior

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How this list is made

Every question here was asked by a real interviewer in a real job interview that a candidate ran MeetAssist in. After the call, the interviewer's questions are pulled from the transcript. Practice sessions, tests, exams and anything that was not a job interview are dropped.

Questions are rewritten so they make sense on their own: names of people, employers and clients are removed, and speech-to-text mistakes are fixed. Small talk, logistics and questions about one candidate's own résumé are left out. Rephrasings of the same question are merged, and the count is the number of different interviews it came up in.

The interviews come from candidates who use MeetAssist, so they lean towards software, data and AI roles: the shares describe these interviews, not every Computer Networks interview. Answers to the most asked questions are written and checked by an editor; a "common mistake" is shown only when reviews of real answers in these interviews show it, with the count.

337 interviews, 208 candidates, Nov 2025 to Oct 2026. Updated every month with new interviews.