Subnetting
Kulani Baloyi / Jul 13, 2024
5 min read
Carving Up the Network : A Guide to Subnetting
First lets recap something do you remember how IPv4 addresses are represented?
They are 32 numbers divided into 4 octets each separated by a dot
What is subnetting?
Subnetting is when we divide a larger network into smaller subnetworks by borrowing bits from the host part of the IP address to create the subnet address.
For example :
255.255.255.0
The subnet mask right here means that the first 24 bits are for the network and the remaining 8 bits are for the host.
Okay cool but why 24 you ask?
Well lets convert that to binary:
Binary | Decimal | Description |
---|---|---|
11111111 | 255 | Network portion (fixed to 1 for /24 subnet mask) |
11111111 | 255 | Network portion (fixed to 1 for /24 subnet mask) |
11111111 | 255 | Network portion (fixed to 1 for /24 subnet mask) |
00000000 | 0 | Host portion (fixed to 0 for /24 subnet mask) |
Notice that we have 24 ones and 8 zeros. The ones indicate the network portion and the zeros that follow indicate the host portion
Another simpler way to represent the subnet mask is as /24 (CIDR notation)
Heres an example, take:
192.168.12.37/28
This means I have 28 bits for the network part and the 4 remaining are for the host part.
To represent the same I.P address and subnet mask in binary form it would work out to be:
IP -> 11000000.10101000.00001100.00100101
Subnet Mask-> 11111111.11111111.11111111.11110000
We can find the network address by performing a bitwise "AND" operation. For this example it would work out to be:
Network Address:
11000000.10101000.00001100.00100000
192.168.12.32
Then if we invert the subnet mask and perform a bitwise "OR" operation, we find the broadcast address:
Broadcast Address:
11000000.10101000.00001100.00101111
192.168.12.47
All addresses in between are our usable IP addresses:
Network Address:
192.168.12.32
Usable Range:
192.168.12.33-192.168.12.46(14 hosts)
Broadcast Address:
192.168.12.47
So why even divide our network?
There are many reasons but some benefits include;
- Improved Efficiency and Organization
- Enhanced Security
- Reduced Network Congestion
- Efficient IP Address Allocation
- Scalability
In summary, subnetting offers a way to create more manageable, secure, and efficient networks. It's a fundamental concept in network administration that helps ensure smooth operation and optimal resource allocation.