SPF, DKIM, and DMARC Explained: How They Work Together
Want SPF, DKIM, and DMARC explained without the vendor sales pitch? Each protocol solves part of email spoofing. Here is what they do, how they work together, and what to set up first.
J. Herwick
How Long Does DNS Propagation Take? A Practical Answer
Wondering how long DNS propagation takes? Most changes go live in 5 to 60 minutes when TTL is set right. Here’s what actually controls the wait — and how to make it minutes.
What Is a DNS Blacklist? (And How to Get Off One)
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.
How to Set Up SPF and DMARC Without Breaking Email
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.
How to Read a WHOIS Lookup (and Why It’s Now RDAP)
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.
How SSL Certificates Work (And What to Do When They Expire)
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.
IP Address Formats: Decimal, Binary, Hex, and How to Convert
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.
Network Basics: The OSI Model Explained in Plain Language
TL;DR — Key Takeaways 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 Pizza … Read more
VLSM and Supernetting: Advanced Subnetting Techniques
TL;DR — Key Takeaways 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 tables. … Read more
What Is a Firewall? Ports, Rules, and Traffic Filtering
TL;DR — Key Takeaways 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 filters … Read more