Real Life Subnetting Example

In this real-life subnetting example, we will focus on a real company network and we will assign ip address blocks to different departments of this company with the help of subnetting. We will do this real-life subnetting example on Cisco Packet Tracer. After this lesson, you will improve your IPv4 subnetting skills and you will be ready for real life subnetting calculations.

 

Our IP Block is 50.5.10.0/24. Here, our subnet mask is 255.255.255.0 (/24). We will use this IP block very efficiently and we will assign IP addresses to the company departments. This company has the below departments and users:

• Engineering (120 Hosts)
• Accounting (40 Hosts)
• HR (20 Hosts)
• Management (10 Hosts)

 

Below, you can see the company network and its departments with the required user ip addresses.

 

 

---

You can check Subnetting Cheat Sheet For Subneeting Calculations.

---

 

First of all, we will determine the department that has highest user number. This is Engineering department. It needs 120 ip addresses for its hosts. To cover these users, we need to divide our IP address block into two with subnetting. Because, to cover 120, we need 128 which means 2 to the 7, 7 host bits. And this means that we will borrow, 8-7=1 bit from the host part of the IP address. So, our new subnet mask will consist of 25 bits as 255.255.255.128 (/25).

 

 

So, with this first subnetting process, our IP block will be divided into two like below:

• 50.10.0/25
• 50.10.128/25

 

Here, we can use the first block for Engineering department. We can use the below host ip addresses for the users in this department:

 

50.5.10.0/25                     Network Address

 

50.5.10.1/25

….

….                                         Host Addresses (126 host addresses)

….

50.5.10.126/25

 

50.5.10.127/25                 Broadcast Address

 

Here, there are totally 128 ip address but 2 of them are network address and broadcast address. So, there are 126 ip addresses are remaining. In the department, we have 120 hosts and for this block we can use these 126 host addresses. The remaining 6 ip addresses will be wasted or will be used by other users in the future in this department.

 

---

Test Yourself With CCNA Practice Questions and Answers!

---

 

Now, we will continue to our subnetting with the remaining block, 50.5.10.128/25.

 

Secondly, we will do subnetting calculations for the second department, accounting department. It needs 40 IP addresses for its hosts. To cover these hosts, we need to have at least 6 host bits. Because, 2 to the 6 is equal to 64 and it covers 40 hosts. 2 to the 5 is not cover 40 hosts because it allows only 32 IP addresses.

 

Here, we need 6 host addresses, so, we need to divide our remaining block into two again. When we divide 50.5.10.128/25 into two with subnetting, we will have the below new blocks:

 

• 5.10.128/26
• 5.10.192/26

 

Here, as you can see, there are 64 IP addresses between these two network addresses (128 +64 = 192). And because of the fact that we have 6 host bits, the remaining 26 bits will be our network bits. So, we will use /26.

 

Here, for the accounting department we will use the first block and the ip addresses for this block will be like below:

 

50.5.10.128/26                 Network Address

 

50.5.10.129/26

….

….                                         Host Addresses (62 host addresses)

….

50.5.10.190/26

 

50.5.10.191/26                 Broadcast Address

 

 

Here, three are 64-2=62 usable ip addresses. 40 of them will be used by the accounting department users and the remaining 22 will be wasted or used in the future.

 

The remaining IP block is 50.5.10.192/26. We will use this block for the remaining two departments.

 

For third department, HR department, we need ip addresses for 20 hosts. To cover these hosts, we need 2 to the 5, 32 host bits. Again, we will divide the remaining block into two. So, after subnetting, our new block will be like below:

• 5.10.192/27
• 5.10.224/27

We will use the first block for HR department. The ip addresses of this block will be:

 

50.5.10.192/27                 Network Address

 

50.5.10.193/27

….

….                                         Host Addresses (30 host addresses)

….

50.5.10.222/27

 

50.5.10.223/28                 Broadcast Address

 

HR department can use 32-2=30 host addresses for its users. There are 20 users, so the remaining 12 ip address will be wasted or used in the future.

 

Now, we will do the last department subnetting calculation and we will divide the remaining ip block, 50.5.10.224/28, into two to use in Management department. For last department, we need 10 user ip address and to cover this, we need 4 host bits. And this will allow us 2 to the 4, 16, ip addresses. These new blocks will be:

• 5.10.224/28
• 5.10.240/28

We will use 50.5.10.224/28 block for this department. It will have 2 to the 4, 16, ip addresses. And 16-2=14 usable ip addresses. Management department needs 10 host ip addresses. So, the remaining 4 will be wasted.

 

50.5.10.224/28                 Network Address

 

50.5.10.225/28

….

….                                         Host Addresses (14 host addresses)

….

50.5.10.238/28

 

50.5.10.239/28                 Broadcast Address

 

Lastly, we will use the remaining block, 50.5.10.240/28. But where? We will use this block on the point-to-point connections between the routers. There are 3 point-to-point connections. This means that there are three more different network in which we need to use different ip blocks.

 

 

To cover these 3 different networks, we will do our last subnetting calculation and we will divide the last remained part into 4. Because, in point-to-point connections, /30 is used. We will also provide this.

 

2 to the 2 is equal to 4. And there will be 4 different blocks. So, these latest blocks will be like below:

 

• 5.10.240/30
• 5.10.244/30
• 5.10.248/30
• 5.10.252/30

 

We will use the first three blocks for the point-to-point connections. And the last one will remain.

 

Yes! We have finished our subnetting calculation for a real company. In this subnetting example, we have efficiently used our ip block and we have assigned ipv4 addresses to the users in the departments with the help of Cisco Packet Tracer. You can do your own network and do subnetting calculations to improve your IPv4 subnetting skills.

 

---

DOWNLOAD Subnetting Cheat Sheet 

---