Category: Network

“You need to open a port.” “Port 443 is blocked.” ── What exactly is this “port number” that keeps appearing in settings screens and error messages? It turns out the IP address, the address of a computer, only carries a parcel as far as the destination machine. Inside it, several…

“The server is down.” “You’ll need to sign up for a rental server.” ── We hear these phrases every day, but what exactly is a server? It turns out a server is not the name of a special machine, but the name of a role: “answer when asked.” Starting from…

A site you updated keeps showing the old version, and support keeps telling you to “clear your cache” ── but what is the cache, really? It turns out the cache is the very reason pages open faster the second time, and the “nothing changed” incident is the side effect of…

The sites and work systems you casually stay logged into ── close the browser, come back tomorrow, and they still greet you signed in. But behind them, the server tends to forget you with every single request. So why are you remembered? The answer is the cookie ── the same…

“As long as it’s HTTPS, you’re safe” ── but how true is that, really? And when HTTP gets flagged as “Not secure”, what exactly isn’t secure about it? HTTPS puts everything between you and a website into a “secret box” that nobody along the route can open ── but how…

You type a URL into the address bar, hit Enter, and the page appears in under a second ── behind that instant, your PC borrows an address, looks up a phone book, entrusts its package to a sorting clerk and the town exit, passes a checkpoint inspection, and receives an…

At home there’s “the router.” Under the office desk there’s a different box with a whole row of LAN ports ── so what’s the difference between the two? The answer lies in how each one uses addresses. A switch hands packages to recipients within the same town (the same network)…

You type in the Wi-Fi password and the web just works ── yet you never entered an address, and someone, somewhere, must be assigning one to your device. That someone is DHCP. This article explains the building-manager mechanism that lends addresses on fixed-term leases: the four-step DORA move-in process, why…

Check “what is my IP” on every device in your house and you get the same value back ── the thing working behind that mystery is NAT (Network Address Translation). This article covers the “translation desk and ledger” mechanism that lets everyone share one global IP, why outside-initiated traffic structurally…

That “Connect VPN” button you click every work-from-home morning ── behind it, your traffic is being sealed into encrypted envelopes and carried through a “tunnel” to the office. This article covers the two problems a VPN solves (snooping on the route, and internal systems being unreachable from outside), how tunneling…