TCP Networking Quiz (Intermediate to Advanced)

Q1. TCP is a reliable, connection-oriented transport protocol that ensures data is delivered in order and without errors between applications. True
False

Q2. Which of the following fields is NOT found in a TCP header? Sequence Number
Acknowledgment Number
Checksum
Time to Live (TTL)

Q3. Which TCP control flag is used to initiate a new TCP connection via the three-way handshake? SYN (Synchronize)
ACK (Acknowledgment)
FIN (Finish)
RST (Reset)

Q4. The TCP three-way handshake involves a client sending a SYN, the server responding with SYN-ACK, and the client replying with an ACK to establish the connection. True
False

Q5. What mechanism does TCP use to prevent a sender from overwhelming a slow receiver’s buffer? Flow control via the receiver’s advertised window
Congestion control via the congestion window
The three-way handshake
Error detection via checksum

Q6. Which TCP flag indicates a request to gracefully terminate a connection? FIN (Finish)
SYN (Synchronize)
PSH (Push)
URG (Urgent)

Q7. In TCP congestion control, which event triggers the fast retransmit mechanism? A single duplicate ACK
Receiving three duplicate ACKs for the same data
An ACK with the ECN-Echo flag
The expiration of the keep-alive timer

Q8. During slow start, TCP’s congestion window (cwnd) grows exponentially, effectively doubling in size each round-trip time until a loss is detected or a threshold is reached. True
False

Q9. Which statement correctly distinguishes between TCP flow control and congestion control? Flow control protects the receiver from buffer overflow, while congestion control protects the network from overload.
Flow control protects the network from overload, while congestion control protects the receiver’s buffer.
Flow control manages packet sequencing, while congestion control handles error detection.
Flow control and congestion control are identical mechanisms.

Q10. Which of the following is true about TCP Cubic? It is the default congestion control algorithm in modern Linux kernels, using a cubic function to grow the congestion window.
It avoids slow start entirely and uses only linear growth.
It predates TCP Reno.
It requires explicit router support to function.

Q11. If a TCP segment is sent but the ACK is not received before the retransmission timer expires, what happens to the retransmission timeout (RTO)? It stays the same for the next retransmission.
It doubles (exponential back-off) for the next retry.
It is reduced by half to retry faster.
The sender switches directly to the fast-recovery phase.

Q12. A receiver advertises a window size of zero during an active TCP connection. What does this indicate? The connection has encountered a fatal error.
The receiver’s buffer is full and it cannot accept more data at the moment.
The sender has entered slow start.
The network is congested and dropping packets.

Q13. During the TCP handshake, each side may advertise its Maximum Segment Size (MSS) option to help avoid IP fragmentation. True
False

Q14. After a TCP connection is closed, the endpoint that sent the final ACK enters the TIME_WAIT state to guard against delayed packets from the old connection. True
False

Q15. How does TCP Reno differ from TCP Tahoe after detecting packet loss via triple duplicate ACKs? Reno enters fast recovery and halves cwnd without dropping to 1 MSS, while Tahoe drops cwnd to 1 MSS and enters slow start.
Reno retransmits all unacknowledged segments, whereas Tahoe retransmits only the lost segment.
Reno ignores triple duplicate ACKs, but Tahoe performs fast recovery.
Reno immediately closes the connection, while Tahoe continues normal operation.

Q16. Which statement about TCP Cubic congestion control is correct? It increases the congestion window purely linearly over time like TCP Reno.
It relies solely on packet loss and does not adjust for RTT.
It grows the window using a cubic function of time since the last congestion event, largely independent of RTT.
It was designed to minimize latency on low-bandwidth networks at the expense of throughput.

Q17. Selective Acknowledgment (SACK) allows a receiver to acknowledge non-consecutive segments so the sender can retransmit only the missing data. True
False

Q18. Which TCP option increases the maximum receive window size beyond the 65 535-byte limit to improve performance on high bandwidth-delay product networks? Window Scaling (RFC 7323/1323)
Selective ACK (SACK)
TCP Fast Open (TFO)
Timestamps

Q19. Explicit Congestion Notification (ECN) allows routers to mark packets instead of dropping them when congestion is detected, and TCP endpoints react by reducing their sending rate. True
False

Q20. Nagle’s algorithm combines small outgoing messages into fewer, larger packets, which can add latency for interactive applications. True
False

system-design