One CN question towers over the rest — walk it well and the round is yours.
"What happens when you type google.com and press Enter?"
- DNS: browser → OS cache → resolver → root/TLD servers → the IP address
- TCP handshake: SYN → SYN-ACK → ACK — connection open
- TLS handshake (HTTPS): certificates verified, session keys agreed
- HTTP request: GET / with headers; server responds with HTML
- Rendering: parse HTML → fetch CSS/JS/images (repeat the above per resource) → paint
Each step is a follow-up hook — know one sentence more about whichever they pick.
TCP vs UDP
- TCP: connection, ordering, retransmission — web, email, files. Reliability over speed
- UDP: fire-and-forget datagrams — video calls, gaming, DNS. A lost frame is better late-ignored than re-sent
OSI in one line each (bottom-up)
Physical (bits/cables) → Data Link (MAC, switches) → Network (IP, routers) → Transport (TCP/UDP, ports) → Session → Presentation (encryption/encoding) → Application (HTTP, DNS). Mnemonic: "Please Do Not Throw Sausage Pizza Away".
Rapid-fire
- HTTP vs HTTPS: TLS encryption — nothing readable on the wire
- IP finds the machine; port finds the program (80/443/22)
- GET idempotent & cacheable; POST neither