Week 12: Day 034 - TCP/IP Basics #5

Hello everybody! Welcome to the entry that will be the second to last in this long chapter. If I'm posting this on Week 12, you might be surprised, because right now it's break, and I've decided to actually spend time on this. But, it's the end of my much needed break, and I feel like I'm ready to dive into this textbook once again.

Last time we were on calculating hosts. Today, I 'm making my first theoretical subnet. Firstly, all of subnetting starts with a single network ID. In my given scenario, I will have to convert 192.168.4/24 network ID inside the hypothetical office from the previous post, into three netowrk IDs. One for the employees, one for the management, and one for wireless users. The primary tool is the existing subnet mask. Remember, from before, write it in binary! At the end of the ones, place a line to seperate them.

Step 1: 11111111111111111111111111|00000000

Draw a second line on digit to the right. This seperates the subnet mask into three areas. The DMS (default subnet mask), the network ID extension (NE), and the hosts (H). Those are not terms which will be in the exam, but they're a useful tip given by author Mike Meyers.

Step 2: {11111111111111111111111111}|{0}|{0000000}
                                 DSM                           NE        H

Now we have a /25 subnet mask. Some would be confused, because surely a subnet mask of /25 can't fit in the three subnets of 255.0.0.0, 255.255.0.0, 255.255.255.0? Well... yes it can. If you remember correctly, subnet masks are binary, which are 1s and 0s NOT 255s and 0s. It was mentioned before, just convert the /25 into dotted decimals. This means 25 ones and 7 zeros (25+7=32).

11111111111111111111111110000000

Then insert periods:

11111111.11111111.11111111.10000000

THEN you convert to the dotted decimal:

255.255.255.128

Next we wanna calculate the subnets. When you're subnetting a network ID, you have no choice and must follow rules made by the developers of TCP/IP to make sure that your subnets will interact correctly with each other, and the larger networks. What you need to remember for subnetting in general is: start with beginning/default subnet, and extend the subnet extension until you have all the subnets you need. To determine how many subnets you created, you have to do 2y where y is the number of bits you added to the subnet mask. Let's do it:

If you move the starting subnet of 255.255.255.0 over one, it's only a single digit, or 2^1

1111111111111111111111111|0|000000
                                           Start  End

The single digit is only a zero or one, which will give you two subnets. But as I said earlier, the office needs three subnets, not two. Now let's take the /24 and make it /26. Extend the network ID two digits to create four new network IDs, 2^2 = 4. To see each network ID, convert the original 192.168.4.0 into binary. Then afterwards add four different network ID extensions to the end of it:

Original network ID: 192.168.4.0 /24
In binary:
11000000.10101000.00000100.00000000

110000001010100000000100|00|00000
110000001010100000000100|01|00000
110000001010100000000100|10|00000
110000001010100000000100|11|00000

Then you convert the four network IDs back to dotted decimal:

Network ID:                                           Host Range:
192.168.4.0/26                                       (192.168.4.1 - 192.168.4.62)
192.168.4.64/26                                     (192.168.4.65 - 192.168.4.126)
192.168.4.128/26                                   (192.168.4.129 - 192.168.4.190)
192.168.4.192/26                                   (192.168.4.193 - 192.168.4.254)

And that's basically now you take a single network ID, 192.168.4.0/24, and subnet it into four new network IDs. Now as we know, the office only needed three, and we have four subnets, so we're wasting one. That will happen, so it's no surprise.

The textbook later goes on to tell me how to manually convert to binary, but I got a calculator, so I can't be bothered right now. If I ever need to know, I'll just go back to the textbook. Now in reality, there's a low probability I'll ever have to do subnetting. It is an important thing to learn, but like many things so far, it's not as important for someone to do in the real world. But why is that?, you may ask. Well to put it briefly there are only two situations where I'd need to do it! #1 If I had to subnet class licenses distributed by the IANA, to customers. #2 Very large customers that take subnets and make their own. Now even though I won't be using it real world, I still need to know it! The most important reason is obvious, for the Network+ exam!!! Then also if I ever have to do my own, or if I decide to pursue a higher level IT certification (hell yeah I will!) which usually assumes you know subnetting.
On that bombshell, I'm done with this entry. I will finish the chapter in class tomorrow. It's short and simple, not much to do. Thanks for reading, and until next time.