So, what's a TCP SACK?

Understanding TCP SACK in networking interviews

This is a straightforward conceptual question on TCP protocol mechanics, commonly asked to assess whether a candidate understands how modern TCP handles packet loss and retransmission efficiency. It tests foundational knowledge rather than complex reasoning, making it a typical warm-up in networking-focused interviews.

The question asks you to define a specific TCP feature and explain its purpose in the protocol stack. To answer well, you should be able to articulate what problem it solves, how it differs from earlier TCP behaviour, and why it matters for throughput and reliability. Interviewers use this to gauge comfort with the TCP/IP model and awareness of performance optimizations in real-world networks.

• TCP retransmission and acknowledgment mechanisms
• Selective vs. cumulative acknowledgments
• Packet loss recovery strategies
• TCP performance tuning