Technical interview guide

OSI & TCP/IP Models

The layered models networking is reasoned about in — physical up to application — and where common protocols and problems live.

Read: 45 min
Practice MCQs: 25
Interview QA: 25
Edition: v4
Editorial status: Reviewed
Relevant for: Network Engineer

Scope: Current IETF host, IPv4, IPv6, ARP, NDP, TCP, UDP, port, ICMP, PMTUD, TLS 1.3, QUIC, and Wireshark references reviewed 2026-09-04.

Interview QA

Treat each question like a live interview question: answer out loud first (structure, assumptions, tradeoffs), then open the model answer to spot gaps and rehearse a tighter follow-up.

Curated: 2026-10-05 · Written: 2026-10-05 · Reviewed: 2026-10-03

QA-1

Compare the OSI and TCP/IP architectural models: where do their boundaries diverge, and how do their end-to-end design assumptions differ in practice?

QA-2

Trace an HTTPS request across a routed network.

QA-3

Explain what addresses a host uses for an off-subnet destination.

QA-4

Troubleshoot IPv6 neighbor and router discovery.

QA-5

Design an application around IP's actual guarantees.

QA-6

Use TTL/Hop Limit and traceroute evidence carefully.

QA-7

Compare IPv4 and IPv6 fragmentation behavior.

QA-8

Diagnose and mitigate a Path MTU failure.

QA-9

Diagnose a TCP connection that cannot complete its handshake.

QA-10

Explain a TCP retransmission trace.

QA-11

Diagnose a slow TCP transfer using window evidence.

QA-12

Design a safe binary protocol over TCP.

QA-13

Investigate unexpected TCP resets.

QA-14

Design a robust protocol over UDP.

QA-15

Explain sockets, listening ports, and ephemeral ports.

QA-16

Design and troubleshoot a protocol through NAT.

QA-17

Create an ICMP filtering policy.

QA-18

Troubleshoot a name that intermittently reaches the wrong service.

QA-19

Validate a TLS server connection securely.

QA-20

Compare TCP+TLS and QUIC for a service.

QA-21

Trace a request through load balancer, TLS proxy, and backend.

QA-22

How does data encapsulation and decapsulation work across the TCP/IP and OSI layers, including the specific PDU names, headers, and layer dispatch keys?

QA-23

Use packet captures as reliable evidence.

QA-24

Design an end-to-end network reliability scorecard.

QA-25