I wasn't getting what I needed from my lesson and turned to google to grasp a better understanding of Subnetting. I'm reading this article : https://support.microsoft.com/en-us/help/164015/understanding-tcp-ip-addressing-and-subnetting-basics

About halfway down the page under **Subnetting** it explains that "The subnet mask 255.255.255.192 gives you four networks of 62 hosts each. This works because in binary notation, 255.255.255.192 is the same as 1111111.11111111.1111111.11000000. The first two digits of the last octet become network addresses, so you get the additional networks 00000000 (0), 01000000 (64), 10000000 (128) and 11000000 (192)....Using a subnet mask of 255.255.255.192, your 192.168.123.0 network then becomes the four networks 192.168.123.0, 192.168.123.64, 192.168.123.128 and 192.168.123.192. These four networks would have as valid host addresses:

192.168.123.1-62

192.168.123.65-126

192.168.123.129-190

192.168.123.193-254

Remember, again, that binary host addresses with all ones or all zeros are invalid, so you cannot use addresses with the last octet of 0, 63, 64, 127, 128, 191, 192, or 255."

What I don't understand is why they are excluding 63, 127, and 191? I've converted those to binary and they aren't all 1's or 0's

63=00111111

127=01111111

191=10111111

In fact, 64, 128, and 192 aren't all 1's or 0's either, are they incorrectly explaining leaving room for a switch or DC or is there another reason to exclude those numbers?

Edit: my binary conversions needed work, but I fixed that