The best way of learning subnetting is to do it. Here are a selection of worked examples to help you get started.

At the end are some links to online quizes so you can do it yourself.

**29.0.0.0**. You need to create at least 20 networks and each network will support a maximum of 160 hosts. Would the following two subnet masks Work?

**255.255.0.0** and or **255.255.255.0**

Yes both would work.

Mask **255.255.0.0** has 8 bits for the subnet and 16 bits for the host

8 bits would accommodate 2^{8}=256 subnets

16 bits would accommodate 2^{16}= over 64000 hosts

Mask 255.255.255.0 has 16 bits for the subnet and 8 bits of the host.

Have possible 2^{8} -2 hosts =254 which is enough

Easiest is to sub net on a byte boundary which would mean a subnet mask of **255.255.255.0**

This would allocate **8 bits** for the **subnet** and** 8 bits** for the **host.**

We need to accommodate around 200 hosts which requires 8 bits which we have.

We need 4 subnets which require 4 bits and we have 8 bits. So we have more than enough.

Decimal 192 =11000000 binary which means that 2 bits of this octet are used for the subnet. Now add the 24 bits 255.255.255 and we have 26 bits. So we write:

222.1.1.20/26

Decimal 248 =11111000 binary which means that 5 bits of this octet are used for the subnet. Now add the 16 bits 255.255. and we have 21 bits. So we write:

135..1.1.25/21

A class C address has 8 bits of the host which will give 2^{8} -2 =254 hosts

Current mask= 255.255.255.0

Bits needs for 10 subnets =4 =2^{4} =16 possible subnets

Bits needs for 12 hosts = 4 = 2^{4} = 16-2=14 possible hosts.

So our mask in binary =**11110000**= **240** decimal

Final Mask =**255.255.255.240**

What is the subnet mask for the maximum number of hosts?

How many hosts can each subnet have?

What is the IP address of host 3 on subnet 2 ?

Current mask= 255.255.255.0

Bits needs for 30 subnets =5 =2^{5} =32 possible subnets

Bits left for hosts = 3 = 2^{3} = 8-2=6 possible hosts.

So our mask in binary =**11111000**= **248** decimal

Final Mask =**255.255.255.248**

Address of host 3 on subnet 2 is

subnet 2 =00010000 host 3 =000000011

Add the two together =00010011=19

therefore IP address of host 3 on subnet 2 =205.11.2.19

What are the two possible subnet masks?

Current mask= 255.255.255.0

Bits needs for 48 hosts = 6 = 2^{6} = 64-2=62 possible hosts.

Bits needs for 2 subnets =1 =2^{1} =2 possible subnets

Total of 7 bits needed so therefore we can use either 1 bit or 2 bits for the subnet. So we could have

1 bit subnet 7 bits hosts or 2 bits subnet 6 bit host

masks are 10000000 and 11000000 =128 decimal and 192 decimal.

Final possible masks are:

**255.255.255.128** and **255.255.255.192**

**255.255.255.192**What is the host address and subnet of the following IP address 197.1.2.67.

192 in binary =11000000 gives 4 possible subnets of (showing 2 most significant bits):

00,01,10,11

67 in binary =01000011

So Applying Mask:

**Videos**

**Related Tutorials and Resources:**

- binary numbers for beginners tutorial
- IPv4 Addresses and Classes
- Subnets and subnet Masking explained.
- Internal and external IP addresses explained
- IPv6 Guide

### Subnet Quizzes

Test you knowledge using these online quizzes

is there any one who can explain the 9th example? i am not getting that ans .

What answer do you get

rgds

steve

Very useful exercises 😉 but I have a question about exercise 6: Shouldn’t it be 255.255.255.248 instead of 255.255.255.240? Because if we choose the last one we will get more than the 12 hosts.

Hi

the answer is correct as 248 would only give us 8 hosts (3 bits) and we need at least 12.

Yes but since it is typed “10 subnets each with a maximum 12 hosts on each subnet.” and 8 is smaller than 12 I assume 255.255.255.248 is the correct answer.

Maximum of 12 means that you can have 12. But with 8 bits you can only have 8.

Does that make sense

rgds

steve

it is very good for beggineer but i need know more focus on the type of the class

Not sure what you mean by type of the class

Sir its a very very help full for beginners and also for experience but i need ur more help to learn total subneting as class a b and c,

Have you watch the videos

IPv4 Addresses and Address Classes Explained

https://youtu.be/nVKZs-_-7U4

———–

IPv4 Subnetting Worked Examples

https://youtu.be/eet6SumgW5A

Were are you struggling? Would it help if I sent you a quiz to test your current understanding?