Walk through the TCP three-way handshake and connection teardown.
Assesses fundamental understanding of Computer Networks conventions, runtime behavior, and memory/performance considerations.
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
TCP opens a connection with a three-way handshake so both sides agree on initial sequence numbers and confirm they can send and receive.
- Client sends SYN with its initial sequence number and options such as MSS and window scaling.
- Server replies SYN-ACK: it acknowledges the client's sequence number and sends its own SYN.
- Client sends ACK acknowledging the server's sequence number; the connection is established.
Client Server
SYN seq=x ->
<- SYN-ACK seq=y ack=x+1
ACK ack=y+1 ->
Two steps would not be enough: each side needs to know the other received its SYN, and the exchange prevents stale duplicates from an old connection being mistaken for a new one. Sequence numbers are randomised to make blind spoofing hard.
Teardown takes four steps, FIN, ACK, FIN, ACK, because each direction closes independently, and the side that closes last waits in TIME_WAIT to absorb delayed segments.
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.