An Address By Any Other Name…

Source and Destination Addresses

When I first got into networking, I found the whole idea of IP addressing to be arcane and mysterious. Keep in mind that during most of my
elementary and middle school years, I was told that math was certainly NOT my thing (the string of C’s seemed to support that). That made me very skittish to even try to grasp things in the numerical arena, and it cast a blanket of fog over the dotted decimal addresses (e.g., 192.168.1.1, 10.2.1.5, etc.)

To be totally truthful, as a visual learner I read and memorized first and had my “aha” moment much later. Granted, there are a
boatload of principles, facts, and figures that just have to be firmly fixed in the brain first, but typically understanding happens at various points along the way. I hope that sharing my own experiences of learning will enable some of you to grasp the concepts more readily than I first did.

First things first, binary is king, as I mentioned much earlier in this blog. All of the seemingly strange things make perfect sense when you
leave behind our familiar decimal/base 10 thinking and get “tw0-dimensional.” At various points I will try to explain the quite-literal “bits and bytes” when it will further clarify some of the networking magic.

There are two ways to typically refer to an Internet Protocol (IP or IPV4) address, either of which you may encounter in various articles, books,
and other technical literature. The first is the use of the address and then the mask/subnet mask, while the second is the network or subnet, with the number of bits used, as follows:

192.168.1.2                 255.255.255.0

192.168.1.2/24

While they look very different, they mean exactly the same thing.  In decimal, each group of numbers between the dots is between 1-255 and is
referred to as an octet because you use 8 binary characters (bits) to create the same number in base-2. We’ll look into the bits involved a little
bit later, but that gives you a beginning point.

IP addresses are grouped into categories referred to as address classes, referred to as A, B, C, D and E. Class D addresses (223.0.0.0 to
239.255.255.255) refer to multicast addresses which are beyond the scope of the CCENT/CCNA but a fascinating topic nonetheless (if interested, read some more on your own). Class E (240.0.0.0 – 255.255.255.255) addresses were experimental and never used in any production setting, and mostly just idle geek-party chatter (just kidding).

Next time we will delve into the A, B and C address classes in more detail

– Joe

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