Protocol questions:
- "Explain the TCP three-way handshake" (SYN, SYN-ACK, ACK)
- "Why does TCP need a handshake?" (synchronize sequence numbers)
- "What's the difference between TCP and UDP?" (reliability, ordering, overhead)
Practical questions:
- "Service A can't connect to Service B. How do you debug?"
- "Website is slow. Where do you start investigating?"
- "How does HTTPS provide security?"
Architecture questions:
- "When would you use L4 vs L7 load balancing?"
- "How does DNS work?"
- "What is a CDN and when would you use one?"
Approach: Explain concepts, mention tools, describe your debugging process.