// Topic collection
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2026-09-22
When working with real projects (changing a CDN, migration, refactoring) you often need to replace one URL with another in bulk. At first glance the task seems trivial: sed -i 's|old|new|g' **/* — and you’re done. …
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Netcat (nc) reads and writes data over TCP and UDP connections. With one small utility it’s convenient to check a port, grab a service banner, transfer a file between machines, or create a temporary tunnel. Below — …
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DNS (Domain Name System) — a distributed system that tells, by domain name, where a website is located, where to deliver mail, and who owns the domain. Each such response is stored in the domain zone as a record of a …
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If your application runs on hundreds of client devices or you have a fleet of sensors with telemetry, sooner or later you’ll need to see what’s happening on the ground. Commercial systems like Splunk or …
Read more2026-09-22
Jitsi Meet — an open platform for video conferencing. It can be connected to Active Directory (AD) so that employees sign in with corporate accounts: you don’t need to create users separately, and disabling an …
Read more2026-09-22
Sometimes all checks pass: ping responds, DNS works, ports are open, mtr shows no loss, but the application still receives errors like connection reset by peer or TLS handshake failed. In those cases you need to look at …
Read more2026-09-22
Simple utilities from previous parts each answer their own question: ping — is there connectivity, traceroute — which path packets take, nc — is the port open. The three tools in this part give a more complete picture: …
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An IP address identifies a host, and a port identifies a specific service on it. A web server usually accepts connections on port 80 (HTTP) and 443 (HTTPS), SSH on 22, databases and mail on their respective ports. A …
Read more2026-09-22
It happens: the computer has an address, the router responds, ping 8.8.8.8 works, but websites in the browser do not open. Most often the cause is DNS — the system that translates domain names into IP addresses. If a …
Read more2026-09-22
When “the internet is not working”, it’s convenient to check from the bottom up: first your own computer and local network, then connectivity to external nodes, then DNS, ports and applications. This …
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