Page 130 Practice Example #6B

[dae26]

I don't quite understand this subnetting example for some reason and maybe it's because it's different. I can kind of see where its going in the table shown but I don't understand what Mr. Lammle means when he says "You actually get two subnets for each third octet value," Does value mean subnet?

9 bits on gives us 512 subnets.
7 bits off gives us 126 hosts.
Valid subnets: 256 - 255 = 1. 0,1,2,3,4,5, etc. This would give me the same subnets as example 5B. And this is where I get lost because I don't know how the 4th octet plays in.

To me, it just looks like we used 0.0, 1.0, 2.0, 3.0, 4.0, 5.0 as the subnets and used the 4th octet of 128 between each subnet (I'm a visual learner so I am thinking about how I write it down) to look something like this: 0.0, 0.128, 1.0, 1.128, 2.0, 2.128, 3.0, 3.128, 4.0, 4.128, 5.0, 5.128, etc.

Looking at the following example the subnet pattern looks like this to me:

3rd octet subnet | 4th octet subnet | 3rd octet subnet | 4th octet subnet etc. instead of the standard class B 3rd octet subnet across the board.

Can anybody shed some light on the example for me. What am I confused about? Am I even making any sense? Maybe it's just super easy and I am expecting more?

Thanks!