IPv4 subnetting is the process of dividing a large IP network into smaller, more manageable sub-networks (subnets).
It helps in efficient IP address allocation, improves security,
and provides better network performance.
Think of it like an office
building. Instead of having one massive, open floor where everyone shouts (a
broadcast domain), you create smaller, private offices and meeting rooms.
Subnetting does the same for your network, creating structured, efficient segments.
For example:
If you have a 192.168.1.0/24 network, subnetting allows you to split it
into smaller ranges like:
- 192.168.1.0/26 (64 addresses)
- 192.168.1.64/26 (64 addresses)
- 192.168.1.128/26 (64 addresses)
- 192.168.1.192/26 (64 addresses)
Why is
Subnetting Important?
Subnetting isn't just a technical
exercise; it delivers tangible benefits for any network.
Efficient IP Usage: Prevents the
waste of IP addresses. Instead of giving one department a massive /24 network
that they'll never fully use, you can allocate a smaller /26 or /27 subnet that
fits their actual needs.
Improved Security: Network
isolation is a key security principle. By placing different departments (e.g.,
Finance, HR, Guest Wi-Fi) on separate subnets, you can control traffic between
them with firewalls, limiting the spread of malware or unauthorised access.
Reduced Network Congestion: Subnetting
creates smaller broadcast domains. Broadcast traffic sent by a device is only
forwarded within its local subnet. This significantly reduces unnecessary
network-wide traffic, improving overall performance.
Better Network Management: Smaller networks
are easier to troubleshoot, monitor, and manage. Problems can be isolated to a
specific subnet quickly, reducing downtime and simplifying admin tasks.
Basic IPv4
Address Structure
An IPv4 address is 32 bits
long, divided into 4 octets (e.g., 192.168.1.1).
It has two parts:
- Network Portion – Identifies
the network.
- Host Portion – Identifies
the device in the network.
Subnetting changes the boundary
between these portions using a Subnet Mask.
Common IPv4
Subnet Masks
|
Subnet Mask |
Number of Hosts |
|
|
/24 |
254 |
|
|
/25 |
126 |
|
|
/26 |
62 |
|
|
/27 |
30 |
|
|
/28 |
14 |
|
|
/29 |
6 |
|
|
/30 |
2 |
(Number of hosts excludes network
and broadcast addresses.)
How to
Calculate a Subnet
Example: You have 192.168.10.0/24
and want to create 4 subnets.
Step 1 – Find the required subnet
bits
- 4 subnets → Needs 2 extra bits (2² = 4).
- New prefix = /24 + 2 = /26.
Step 2 – New subnet mask
- /26 → 255.255.255.192.
Step 3 – Find block size
- 256 - 192 = 64 (each subnet has 64
addresses).
Step 4 – List subnets
- 192.168.10.0 → Hosts: .1 to .62 (Broadcast: .63)
- 192.168.10.64 → Hosts: .65 to .126 (Broadcast: .127)
- 192.168.10.128 → Hosts: .129 to .190 (Broadcast:
.191)
- 192.168.10.192 → Hosts: .193 to .254 (Broadcast:
.255)
Benefits of
IPv4 Subnetting
- Better control over traffic flow.
- Isolation for different departments
or services.
- Optimised use of available IP addresses.
IPv4
subnetting is a powerful and essential technique for any network administrator.
It moves you from having a flat, inefficient network to a structured, secure,
and high-performance one. By understanding the basic address structure,
learning to interpret subnet masks, and practicing the calculation steps, you
can master subnetting and design robust networks that make the most of your
available IP address space.
