Networking & Protocols
IP packets: free-recall review
Retrieval beats re-reading. For each prompt, say or write a full answer from memory before you open the model answer — the effort of recall is what makes the mechanism stick.
Reconstruct the unit’s spine — best-effort delivery, longest-prefix forwarding, TTL and traceroute, PMTUD black holes, what NAT breaks, and how BGP/spoofing defences work — without looking back at the lessons.
- 01Why is IP deliberately best-effort and connectionless, and what does that design push onto the layers above it?
- 02Explain longest-prefix match and why the routing table is split from the FIB.
- 03What is TTL, what happens when it reaches zero, and how does traceroute exploit that?
- 04What is a PMTUD black hole, why does it produce the 'small requests work, large ones hang' symptom, and what is the robust fix?
- 05What does NAT break and why, and why is 'NAT is a firewall' a dangerous misconception?
- 06IP authenticates neither source nor route. Name the spoofing and hijack defences and why each needs operator cooperation.
If you could reconstruct each answer from memory, you hold the unit’s spine: IP is best-effort by design and pushes reliability to TCP/QUIC; forwarding is longest-prefix match split across a control-plane routing table and a hardware FIB; TTL caps hops and powers traceroute; a blocked ICMP turns a path-MTU mismatch into a silent black hole that MSS clamping fixes; NAT trades address relief for broken end-to-end reachability and is not a firewall; and because IP authenticates neither source nor route, BCP 38/uRPF and RPKI are the defences — effective only where operators cooperate.