Articles & Guides

How to find a server port: which port your service listens on in Linux, Windows and macOS, which port a host answers on, and where the proxy port lives. Real commands.

How to find an IP address: public vs local, your computer on Windows, macOS and Linux, the router gateway and any server. Real ipconfig, ip a, dig and nslookup commands.

How a static IP differs from a dynamic one, how to tell a public address from CGNAT, how to check which one you have and what to do if a static IP is unavailable.

What a subnet mask is and how to read /24 and 255.255.255.0: a mask table with host counts, network and broadcast calculation, reserved ranges and where it matters.

How to check ping to a server, website, or your internet connection: the ping command on Windows, macOS, and Linux, online ping from another network location, a table of normal ping values, and a diagnostics checklist for high or unstable ping.

Cloudflare in Russia 2026: is Cloudflare blocked in Russia, why sites behind Cloudflare fail to load from Russian networks (TLS ECH), the risks for owners with Russian audiences, local CDN alternatives, and a step-by-step migration plan with DNS and SSL checks.

ERR_ADDRESS_UNREACHABLE means the IP resolved but there is no route to it. Learn the causes — router, VPN, IPv6, private IPs — plus diagnostics and fixes.

How to check open ports: netstat and Get-NetTCPConnection on Windows, ss and lsof on Linux, nc and telnet from outside, plus a free online port scanner.

SMTP errors 550 and 554 explained: what the codes mean, enhanced 5.x.x status codes, rejection causes (SPF, DKIM, DMARC, blacklist) and how to fix them fast.

What MTU and MSS are, typical values (1500, 1492, jumbo 9000), Path MTU Discovery and black holes. How to measure MTU with ping and set it on your OS.