Need to remove your IP from an email blacklist? Spamhaus, Barracuda, and SpamCop each have different processes. Here is what a DNS blacklist actually is, why SORBS no longer matters, and the steps that work.
Need to set up SPF and DMARC without breaking email delivery? The safe order matters more than the records themselves. Here is the staged playbook — inventory senders first, publish in order, monitor before enforcing.
Want to know how to read a WHOIS lookup today? The protocol is actually RDAP now. Here is what registration data shows, why most fields are redacted, and how to spot red flags.
Want to know how SSL certificates work without the marketing fluff? They prove a server’s identity using a chain of trust. Here is what changed in March 2026, and what to do when one expires.
Master IP address formats: dotted decimal, binary, hexadecimal, and integer. Learn to convert between them by hand, identify IP classes, and see why format parsing ambiguity has caused real security bugs.
TL;DR — The Short Version The OSI model is a 7-layer reference framework that describes how data travels between applications across a network. It is not software you install or a protocol you configure. The seven layers, bottom to top: Physical, Data Link, Network, Transport, Session, Presentation, and Application. Mnemonic: Please Do Not Throw Sausage … Read more
TL;DR — The Short Version VLSM (Variable Length Subnet Mask) divides a network into subnets of different sizes. Each subnet matches its real host count. Fixed-length subnetting (FLSM) wastes addresses by forcing every subnet to the same size. Supernetting (route aggregation) is the reverse. It combines contiguous networks into one larger block to shrink routing … Read more
TL;DR — The Short Version A firewall monitors and controls network traffic based on a predefined set of rules. It sits between trusted and untrusted networks. Decisions come from packet headers. Source and destination IP, port numbers, and protocol determine whether traffic is allowed, denied, or dropped. Types range from simple to deep. Stateless packet … Read more
Learn to troubleshoot network connectivity with a systematic 7-step method that works every time. Start at the physical layer and work up through IP, gateway, DNS, and firewall checks, with the exact commands to run.
Understand the IPv4 vs IPv6 differences with a 2026 perspective. Learn why IPv4 ran out, how IPv6 solves it, and what the March 2026 majority milestone on Google means for your network.