Most interview prep lists give you a definition to memorize. That's not what gets you hired. Interviewers ask these to find out how you think — whether you can reason through a system, admit what you don't know, and stay organized when something's on fire.
So each question below has the answer, and then the more useful part: what they're actually testing.
Browser checks its cache, then resolves the domain via DNS (local cache → resolver → root → TLD → authoritative). It opens a TCP connection to the resulting IP on port 443, performs the TLS handshake, sends an HTTP request, gets a response, and renders it — pulling additional assets as it parses.
TCP is connection-oriented: handshake, ordered delivery, retransmission of lost packets. Use it when correctness matters — web, email, file transfer. UDP is fire-and-forget: no handshake, no guarantee. Use it when timeliness beats completeness — voice, video, DNS queries, game traffic.
Authentication is proving who you are. Authorization is what you're allowed to do once you've proven it. You authenticate once and get authorized many times.
Scope it first: one user or everyone? One site or all sites? Then work up the stack — is the machine on the network (link light, IP address)? Did it get a real IP or a 169.254 address, which means DHCP failed? Can it ping the gateway? Can it resolve a name (`nslookup`)? Can it reach an IP directly? That last split tells you DNS versus routing.
It's the phone book of the internet. You know the name; DNS gives you the number the network actually needs. Your machine asks a resolver, which asks its way down the hierarchy until something authoritative answers, and the result is cached along the way so it's fast next time.
TLS does three things: it encrypts the traffic so a middleman can't read it, it verifies the server's identity via a certificate signed by a trusted authority, and it detects tampering in transit. Asymmetric crypto is used to agree on a shared key; the actual data is then encrypted with faster symmetric crypto.
Confidentiality (only the right people see it), Integrity (it hasn't been altered), Availability (it's there when needed). Most security controls exist to serve one of the three, and they trade off — locking something down harder often costs availability.
Symmetric uses one shared key — fast, but you have to get the key to the other side safely. Asymmetric uses a public/private key pair — slower, but solves key distribution. Real systems use both: asymmetric to exchange a key, symmetric for the bulk data. That's exactly what TLS does.
Layered: MFA so stolen passwords alone don't work, mail filtering and external-sender banners, a verification rule that any payment change gets confirmed by phone on a known number, and training that makes reporting easy and blame-free. Assume someone will eventually click, and design so that click isn't fatal.
Use the shape: situation, what you did, what happened, what you changed afterward. Keep it to ninety seconds. If your example is from a homelab rather than a job, say so plainly — nobody minds, and it beats a vague hypothetical.
The IT & Security Interview Answer Bank — the full set of questions with real answers, written to be read the night before. Instant download.
Get the answer bank — $5 →Brush up on the two things you'll most likely be asked to recite: the ports and protocols reference and the subnetting cheat sheet. Landed the job? First 30 Days in a New IT Job covers the part after the offer.