Subnetting Tables and Tools

Subnetting can be ponderous. This post acts as a repository for subnetting information that is pertinent to certification exams and is important for the job. It contains subnetting tables for IPv4 class A, B, and C networks. It also has various links including two of my favorite subnetting calculators.

Watch my introductory lesson on subnetting here:


– Online IP Subnet Calculator: An excellent […] read more

Home Security Tips – Beyond the Security Alarm


A student of mine was concerned with potential break-ins and theft, and recently asked me about home-based wireless alarm systems and if they are secure. I told the student that anything can be compromised given some brains and perseverance. But with the right mindset, a wireless alarm can very well increase the security of a home. However, I like to think of an […] read more

Microsoft updates password checker program

I’m not sure exactly when it happened, but the Microsoft password checker at the Safety & Security Center has increased it’s requirement for strong passwords. Just a year ago, a password such as |ocrian7 (which I show in my A+ Exam Cram) was considered “strong”. Now, it’s considered to be “weak.” It’s an inevitable sign of the times. Password cracking programs and the computers that […] read more

MACs, Hashes, and Digital Signatures

I often get this question from students: “What’s the difference between MAC, Hashes, and Digital Signatures?” So I thought I’d write a short article about it. For more about these topics, get my CompTIA Security+ Cert Guide today!

First let’s give a short description of each:

• Cryptographic hash functions: This is a procedure that calculates a fixed-size bit string (hash value) from a piece […] read more

c99 Shell Trojan

The C99Shell (and its cousin web shells) can be devastating. This is an extension article that stems from Chapter 2 of the CompTIA Security+ SY0-301 Cert Guide (2nd Edition).

One of my associate’s websites was hacked into. He contacted me to see if I knew anything about a Web Shell. He had found that name within the syntax of one of the “new” files on […] read more

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