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Closed and Filtered Aren't the Same Finding
NAT and Port Forwarding for Home Networks: Why "Filtered" Doesn't Mean "Firewalled"
Most home network ports show "filtered" from the internet — not because of a configured firewall, but as a side effect of how NAT works: incoming connections without an existing mapping have nowhere to go. Here's the open/closed/filtered distinction, how NAT creates this effect, why port forwarding and UPnP change it, and the CGNAT limitation that can make port forwarding fail entirely.
Reverse DNS for IPv4 vs IPv6: Why ip6.arpa Delegation Works So Differently from in-addr.arpa
IPv4 and IPv6 reverse DNS use the same in-addr.arpa/ip6.arpa concept — but IPv6's vastly larger address space means most addresses simply don't have PTR records, by practical necessity rather than oversight. Here's how each zone's delegation works, who controls PTR record configuration, and why "no PTR record" is a much more common and unremarkable result for IPv6.
IPv6 Address Types: Why One Interface Has Link-Local, ULA, and Global Addresses All at Once
A single IPv6 interface normally has 3-4 different addresses simultaneously — link-local, unique local (ULA), and one or more global unicast addresses, each with different scope and purpose. Here's what each address type does, why ULAs exist alongside global addresses unlike IPv4's NAT model, and why privacy extensions cause global addresses to rotate.
ICMP and Ping: Why It Has No Ports, Why It's Blocked, and What "Ping Failed" Actually Tells You
Ping uses ICMP — a protocol with no ports, no connections, and no relationship to whether a web server or any other application is actually working. Here's why ping is so commonly blocked by firewalls, what ping success/failure actually tells you (and doesn't), and how blocking the wrong ICMP message type can cause silent, hard-to-diagnose connection failures via Path MTU Discovery.
BIMI Certificates Explained: VMC, CMC, and the Trademark Verification Chain
A BIMI logo in an inbox is the endpoint of a verification chain that can include a Verified Mark Certificate — a specific X.509 certificate type tied to trademark registration, issued by a small number of specialised Certificate Authorities. Here's what's actually in a VMC, the CMC alternative, BIMI's restricted SVG logo format, and how it all depends on DMARC enforcement underneath.
Network Diagnostics: The Systematic Workflow From Ping to Port Scan
A systematic diagnostic workflow finds network problems in minutes: ping → DNS lookup → traceroute → port scan. Each tool answers a specific question and eliminates a layer. Here's the complete process, what each result means, and how to distinguish local problems from remote ones.
Cloud Security Groups: AWS, GCP, Azure — Common Misconfigurations and How to Audit Them
Every major cloud breach has the same pattern: legitimate infrastructure, misconfigured security groups. Here's how AWS Security Groups, GCP Firewall Rules, and Azure NSGs work, the most common dangerous misconfigurations (databases open to 0.0.0.0/0), and why scanning your own cloud infrastructure is security hygiene.
Email Provider Migration: The Correct MX Record Sequence to Avoid Losing Email
Switching email providers is one of the most common causes of lost email. Here's the correct migration sequence (never update MX first), how Google Workspace, Microsoft 365, and Zoho Mail configure their MX records, and how to verify after migration.
IP Geolocation: How It Works, Why City-Level Accuracy Is Unreliable, and the VPN Problem
IP geolocation is 95–99% accurate at country level and 50–80% accurate at city level — and VPN users are always wrong by design. Here's how geolocation databases work, the legitimate business uses, the VPN problem for geo-dependent services, and what an IP lookup actually reveals beyond location.
DNS Providers Compared: Cloudflare vs Route 53 vs Google Cloud DNS — and Why It Matters
Registrar DNS is almost always the weakest option — slow global performance, poor TTL flexibility, and limited routing features. Here's how Cloudflare, Route 53, and Google Cloud DNS compare on performance, pricing, and features, and how to move DNS without moving your domain registration.
DNS as a Security Tool and Target: Cache Poisoning, Hijacking, and DNSSEC
DNS cache poisoning, DNS hijacking, and DNS tunneling are real attack vectors. Here's how each works, what DNSSEC does (and doesn't) protect against, how to monitor your own DNS records for unexpected changes, and what domain shadowing is.
Domain Squatting and Typosquatting: How to Detect and Defend Against Brand Impersonation
Typosquatters register domains like examp1e.com and brand-support.com to phish customers and intercept traffic. Here's the patterns attackers use, how to monitor for lookalike registrations using CT logs and DNSTwist, defensive registration strategy, and UDRP dispute resolution.
