Subnetting 101 (Overview)
I will now be doing a subnetting tutorial in a nutshell in order to help those pips who are also inclined to my field. So first and foremost, let us start by defining some few terms. Some of the definitions are of my own words for simplicity’s sake and some might not be reflected in some books or reviewers. This tutorial is made with the assumption that the reader knows how to convert IP Address from Decimal to Binary or vice versa.
This is Decimal, 10.1.23.19.
This is Binary, 00001010.00000001.00010111.00010011.
The two IP addresses are identical but of different format.
Network - a group of two or more computer systems linked together.
Subnetwork - is commonly called as subnet, is a subdivision of an IP network. Which in we use it in a pie analogy, the pie would be the network and the slices in the pie would be the subnetworks.
Subnet mask - a 32-bit combination that would describe the portion of the subnet and the portion of the host.
Host/User - a computer or another device that is connected to a network.
Prefix Length - is the number of bits set in the subnet mask. Your prefix length will determine you subnet mask. The reverse is also possible by converting your subnet mask to binary and counting the number of 1’s in the set.
Subnetting - the practice of dividing a network into two or more networks.
Ayala has a Network IP of 192.168.0.0/24. Ayala needs 3 subnetworks namely: Net A, Net B and Net C. Net A have 20 users. Net B have 10 users. Net C have 10 users. Provide the subnetworks that would accommodate Ayala’s needs.
Steps in Solving the Problem:
Given this question, we will now use the 5 basic fundamental questions in problem solving.
What operation to be used?
Is this your final answer?
The subnetworks that would accommodate Ayala’s needs.
Network IP - 192.168.0.0/24
What operation to be used?
Unlike in mathematics were we have multiple operations to choose from, we will be followings steps here instead of choosing operations. There is actually no sequence that was taught in the books or reviewers but I follow this sequence that I came to be quite fond of after four years of doing it. It is straight forward and easy to follow step that I put together.
Why do we need to validate the Network IP? We need to verify if the Network IP is valid because some professors test their student’s analysis. Some professors will put an invalid Network IP so the problem will be invalid in an instant. Most students will just solve the problem without even considering if the problem was actually valid. This will result to waste of time especially during exams when you realize later after solving that the Network IP could not handle the client’s needs. (How to validate Network IP will be discussed in details in another post.)
Determine the biggest needed Network (Subnetting)
Now that you already validated your Network IP, you can start subnetting. In order to have a organize flow, we need to get the biggest needed network out of the client’s demand. In our sample problem that would be Net A since it has 20 users. (How to subnet a given IP will be discussed in details in another post.)
After subnetting the given Network IP, you will get 8 subnet IPs that could handle 30 users each with a prefix length of /27.
We will now assign the first set for our Net A. So our Net A will now be using the IP set - 192.168.0.0/27.
Technically, we can use the remaining sets to assign to Net B and Net C since each subnet IP could handle 30 users. But in making an effective network plan, this is considered a bad practice since you will be wasting 20 users resource on each subnet because you will only be using 10 valid IPs for each.
To correct this, we need to subnet again the next subnet IP ( 192.168.0.32/27 ) in order to maximize the resource that we have.
After subnetting the next subnet IP, you will get 2 subnet IPs that could handle 14 users each with a prefix length of /28.
We will then now use these two subnet IPs with 14 users capacity to our remaining needed networks which are Net B and Net C.
From our subnetting process. We can now produce a solution which is:
Is this your final answer?
Normally, this is an enough solution and your professor will already understand this. However, as a student, we need to secure our grade so just to be on the safe side we will need to dissect this into a more detailed solution.
How? We simply present it in this format:
General IP: (Given Network IP)
Network Name: (Given Needed Network)
Network IP: (Subnetted IP for this Network)
First Usable: (First Usable IP of this Subnet)
Last Usable: (Last Usable IP of this Subnet)
Broadcast: (Broadcast Address of this Subnet)
So our final answer will look like this:
General IP: 192.168.0.0/24
Network Name: Net A
Network IP: 192.168.0.0/27
First Usable: 192.168.0.1/27
Last Usable: 192.168.0.30/27
Broadcast: 192.168.0.31/27
Network Name: Net B
Network IP: 192.168.0.32/28
First Usable: 192.168.0.33/28
Last Usable: 192.168.0.36/28
Broadcast: 192.168.0.37/28
Network Name: Net C
Network IP: 192.168.0.48/28
First Usable: 192.168.0.49/28
Last Usable: 192.168.0.62/28
Broadcast: 192.168.0.63/28
And there you go! This is an overview of how you will solve a subnetting problem. (How to determine the FUA/LUA/BA will be discussed in detail on another post.)
Congrats! Happy Subnetting!
