TRUE FORM OF SUBNET
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For you to know the subnet number that you need
You have to find the borrowed bits first
For you to know the host number that you need
You have to find the host bits first
THE BORROWED PORTION OF THE IP ADDRESS
How to find number of subnet
# x number of borrowed bits
2^x THE HOST PORTION OF THE IP ADDRESSS
How to find number of host
OR Just count the remaining host bits after you borrowed bits from finding subnet
# Number of host bits since network add & broadcast add
2^n - 2
Great example
10.217.182.223/11
network address = ?
broadcast address = ?
first usable address = ?
last usable address = ?
number of host (usable) address = ?
First step:
10.217.182.223 /11
# First we have to convert the 217
# Why we only convert the 2nd octet to binary?
# Because it is /11 which is located in 2nd octet
10.11011001.0.0 = 10.217.0.0
# Convert the remaining network portion of the address from /11
10.11000000.0.0 = 10.192.0.0 network addressLike this
Second step
For the first usable address
Just add a 1 into the last octet
Third step
For broadcast address
# JUST CONVERT THE REMANING HOST BITS ALL TO 1
# From
10.11011001.10110110.11011111 = 10.217.182.223
# To
10.11011111.11111111.11111111 = 10.223.255.255 broadcast address
Fourth step
For you to determine the usable hosts
# We have 21 host bits which is the orange
# -2 since we have to exclude the network address and broadcast address
2^21 - 2 = 2,097,150 usable hosts per subnet
Example:
10.0.0.0/8 ===== 2000 subnets
# 11 is the borrowed bits
2^11 = 2048 subnets11 borrowed bits means /19
# 19 is the position in octets
# 32 is the overall count for 4 octets (8+8+8+8)
19 - 32 = 13 remaining host bits13 is the host bits
# -2 since we have to exclude the network and broadcast address
2^13 - 2 = 8190 hostsNow we have
2048 subnets === 8190 hosts
Example:
You need to divide this network into 5 subnets
192.168.255.0/24 ====== 5 subnets
First step:
We have to find the right subnet to us. We will borrow to the host portion of the IP
# In binary form the last octet
# Why the last octet only?
# Because it starts with /24
# So you dont have to touch other octets
192.168.255.00000000 Then we will find the subnet using this formula
# x is the borrowed bit from host portion
2^xLet's try finding number of subnet
2^1 = 2 subnet
2^2 = 4 subnet
# We will stop since we got 8 it will be enough for 5 subnets
2^3 = 8 subnetThe 3 is the borrowed bits 3 which means /27 in binary format
Our new IP address and prefix
192.168.255.0/272^3 = 8 subnets
0 0 0 0 0 0 0 0
128 64 32 16 8 4 2 1Second step:
You will just put 1 in the specific target like /27 or in order number 27
After that you just have to +32 +32 +32 +32
Why 32? Because it is on slot 27 or /27 (see it in binary form, count it)
If it is /26 then it will be +64 +64 +64 +64
If it is /28 then it will be +16 + 16 +16 +16
192.168.255.00000000 = 192.168.255.0 network address
192.168.255.00100000 = 192.168.255.32 network address
192.168.255.01000000 = 192.168.255.64 network address
192.168.255.01100000 = 192.168.255.92 network address
192.168.255.10000000 = 192.168.255.128 network address
# THE OTHER 3 SUBNET WHICH IS EXTRA
192.168.255.160 network address
192.168.255.192 network address
192.168.255.224 network address
OVERALL = 8 SUBNETS
BUT YOU ONLY NEED = 5 SUBNETSExample:
what subnet does 172.21.111.201/20 belong to?
ANS: = 172.21.96.0 network address
172.21.01101111.0 = 172.21.111.0
# Just turn 0 the host portion of the IP
# Except /20 backwards
# So 64 + 32 = 96
# That is why we have 96 in IP
172.21.01100000.0 = 172.21.96.0 network addressExample:
What is the broadcast address of 192.168.91.78/26 belongs to?
ANS = 192.168.91.127 broadcast address
192.168.91.01001110 = 192.168.91.78
# Just put flip 1 in /26 or slot 26
192.168.91.01000000 = 192.168.91.64 network address
# Just flip the 0 to 1 for you to get the broadcast address
192.168.91.01111111 = 192.168.91.127 broadcast addressLast updated