Lets take Class A IP 12.0.0.0, Now we have to provide subnet ID for all five Interfaces as shown in above picture. Hence five new network is required in our design of network.

Now we have take class A IP address try to understand the steps.

### Steps for Subnetting questions

1 write down the given class A IP 12.0.0.0

2 We know that this is class A IP hence first octet is reserved for network and three octet are reserved for host see below picture.

Keep Network part as it and convert host part into binary, Then it will be like this.

IP address 12.00000000.00000000.00000000 ( host id converted into binary )

Now check the maximum number of IP required among the five new network interface,

Here in this case 60 PC interface is maximum number required.

Select maximum value interface to design network, small will be adjusted itself.

3 write the equation 2ⁿ -2 ≥ maximum value interface so in this case we can write

2ⁿ -2 ≥ 60 , Put n =1, 2, 3, 4,….. so on such that the value of n which must satisfy this equation.

If we put n =1 which will not satisfy

if we put n= 2 , n =3, n= 4, n= 5, ( all these value of n will not satisfy the above equation ).

But n = 6 then equation will become 2⁶ -2 ≥ 60 or 62≥60 this is correct, Hence value of n =6 satisfy the equation.

4 Now write IP 12.**00000000.00000000.00000000**

Now you have to reserved 6 bits for host from left side, Rest make the values 1,

Science network bits represented by 1 and host bits represented by 0 . If i am making host bits 1 then its mean that , I am giving host bits to network and this is called subnetting, Then it will look like this.

5 IP address **12.11111111.11111111.11000000 **now convert this binary bits into decimal then we will get 12.255.255.192

6 what will be subnet mask for 12.255.255.192 ?

We know that subnet mask for class A by default is 255.0.0.0, Hence subnet mask for

12.255.255.192 will be 255.255.255.192 because you have changed host bits to network bits so it will be not same as by default.

Now if you want to write CDIR value, Hare count how much bits for network is used in IP address, Here in this case total network bits 8+8+8+2 = 26 .

Hence first subnet ID will be 12.0.0.0/26 so its subnet mask will be 255.255.255.192

## How to make next subnet mask ?

↓

Now take the first bits of 1 from left to right in IP **12.11111111.11111111.11000000 **

Find the decimal value of that 1 , So its decimal value is 64.Add this value into first subnet ID 12.0.0.0/26, then it will be 12.0.0.64

Hence Subnet ID -2 will be 12.0.0.64/26.

First subnet ID = 12.0.0.0/26

Second subnet ID = 12.0.0.64/26 ( broadcast ID will be 12.0.0.63 )

Third subnet ID = 12.0.0.128/26 ( broadcast ID will be 12.0.0.127 ) one less than maximum value.

fourth subnet ID = 12.0.0.192/26 (broadcast ID will be 12.0.0.191 ).

Now we have found four subnet ID, But we have five new network, So we required one more subnet ID . So add 64 in 4th subnet ID hence 192 +64 = 256, this value is not possible because maximum value in any octet will be 255.

So for this you have to do like this.

Use watch concept, How time in watch change.

**4 : 59** pm here m is minute and s is second, When one minute increase then watch not show like 4 : 60 , It shows **5 : 00**

Hence here same watch concept will be use, when reach maximum value so this is main concept. Now we can write fifth subnet ID.

**Fifth Subnet ID = 12.0.1.0/26 subnet mask 255.255.1.255**

Sixth Subnet ID = 12.0.1.64/26 subnet mask 255.255.1.64

seventh subnet D = 12.0.1.128/26

eighth Subnet ID = 12.0.1.192/26

ninth subnet ID = 12.0.2.0/26 and so on

Last Subnet ID is 12.255.255.192/26

Now suppose you have an IP 200.10.20.10/26 then question is how many maximum host can link to this or how many computer we can add to this subnet ID.

Ans It is simple first you see which class IP is this, So this is class C IP now in class C IP three octet are reserved for network and one for host so total 32 bits.

But as per CIDR value it is clear that here 26 bits are used for network, So 32 – 26 = 6 bits are left for host .

Hence number of computer can be add to this subnet ID will be 2⁶ – 2 = 64- 2 = 62

So we can connect 62 maximum computer to this subnet ID.

We will continue in next post.I hope you have enjoyed to learn subnetting questions if you like comment and share on social media thanks for reading and sharing keep learning more and more

Dated 27th Oct 2018

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