Subnetting
Simple Steps to perform Subnetting:
You have a class C address of 192.168.100.0/24. You need 9 Subnets
-What is the IP plan of network numbers;
-broadcast numbers
-valid host numbers
-Subnet mask needed for this plan
Step1:
Determine how many H bits you need to borrow to create 9 valid subnets
2N-2 >= 9
N=4, so you need to borrow 4 H bits and turn them into N bits
Start with 8bits HHHH HHHH
Borrow 4 bits NNNN HHHH
Step2: Determine the first valid subnet in binary
0001 HHHH Cannot use subnet 0000 because it is invalid
0001 0000 Subnet Number
0001 0001 First Valid Host Number
.
.
.
.
.
0001 1110 Last Valid Host number
0001 1111 Broadcast address
Step 3: Convert Binary into Decimal
0001 0000=16
0001 0001=17
.
.
.
.
0001 1110=30
0001 1111=31
Step 4: Determine the second Valid subnet in binary
0010 HHHH 0010=2 in binary=second valid subnet
0010 0000 Subnet work number
0010 0001 First valid host number
.
.
.
.
.
0010 1110 Last valid host number
0010 1111 Broadcast number
Step 5 Convert binary into decimal
0010 0000=32 Subnetwork
0010 0001=33 First Valid host number
.
.
.
.
0010 1110=46 Last Valid Host number
0010 1111=47 Broadcast number
Step 6: Create an IP plan table
Valid subnet Network Number Range of Valid Hosts Broadcast number
1 16 17-30 31
2 32 33-46 47
3 48 49-62 63
Step 7 Finish the IP plan table
Subnet 0 192.168.100.0
192.168.100.15
Subnet 1 192.168.100.16
192.168.100.31
Subnet 2 192.168.100.32
192.168.100.47
Subnet 3 192.168.100.48
192.168.100.63
Subnet 4 192.168.100.64
192.168.100.79
And the list goes on……
Step 8 Calculate the subnet mask
Default Subnet mask for Class C is 255.255.255.0
i.e 1111 1111.1111 1111.1111 1111.0000 0000
We have borrowed 4 bits. Therefore
1111 1111.1111 1111.1111 1111.1111 0000
i.e 255.255.255.240
Subnetting Class B is also very much similar to this, but we have to start with 16 Host bits
Eg
If N=4
Start with 16 H bits HHHH HHHH.HHHH HHHH
Borrow 4 bits NNNN HHHH.HHHH HHHH
