· dns, domains
WHOIS lookup explained: what's actually in a domain registration record
WHOIS is the public directory of who owns a domain. Here's what each field means, why some of them are redacted, and how to read a registration record.
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Practical, no-fluff guides for sysadmins and IT pros. Each article ties to a free tool you can use right now.
- · dns, networking
How to check DNS propagation (and how long it actually takes)
Just changed an A record and your friend in another country still sees the old site? That's DNS propagation. Here's how to verify when it's actually done — and how long it can take.
- · networking, security
How to read an open port (and when to actually worry)
An 'open port' isn't a vulnerability by itself — it's information. Here's how to tell whether a port being open is fine, suspicious, or actively dangerous, and what to do about each case.
- · tls, ssl
How to check an SSL/TLS certificate (and what to look for)
Every HTTPS site relies on a TLS certificate. Here's how to read one, what each field actually means, and the things that should make you suspicious.
- · email, security
DMARC, SPF, and DKIM explained (and why you need all three)
Email spoofing is trivially easy without email authentication. Here's how SPF, DKIM, and DMARC work together — and how to check yours.
- · networking, privacy
What is my IP address, and why does it matter?
Your public IP is the address the rest of the internet uses to talk to you. Here's what it reveals, what it doesn't, and how to check it.
- · networking, subnet
Subnet calculator cheatsheet: CIDR, masks, and host counts
A quick-reference for IPv4 subnet math — how to read a CIDR, what the mask actually means, and the easy way to count usable hosts.
- · dns, networking
How to do a DNS lookup (and why you'd want to)
DNS lookups are the first step in almost every network troubleshooting flow. Here's how they work, the record types that matter, and how to run them from your browser.