====== Subnetting ======

**Subnetting** is the process of dividing a large IP network into multiple smaller networks, called **subnets**.

Subnetting improves network organization, security, and routing efficiency.

-----

===== Why Is Subnetting Needed? =====

Without subnetting, every device would belong to one large network.

As networks grow, this causes:

  * More broadcast traffic
  * Reduced performance
  * Difficult management
  * Poor security

Subnetting divides a network into smaller, more manageable sections.

-----

===== An Example =====

Suppose a company owns the network:

<code>
192.168.1.0/24
</code>

Instead of placing all devices into one network, it can create several subnets.

Example:

<code>
Office A

192.168.1.0/26

Office B

192.168.1.64/26

Office C

192.168.1.128/26

Office D

192.168.1.192/26
</code>

Each subnet functions as an independent network.

-----

===== What Is a Subnet? =====

A subnet is a group of devices that share the same network prefix.

Devices within the same subnet can usually communicate directly.

Communication between different subnets normally passes through a router.

<code>
Subnet A
192.168.1.0/26
        │
        ▼
      Router
        ▲
        │
Subnet B
192.168.1.64/26
</code>

-----

===== Network Prefix =====

Every IP address contains two parts:

  * Network portion
  * Host portion

Example:

<code>
192.168.1.25/24

Network

192.168.1

Host

25
</code>

The prefix length determines how many bits belong to the network.

-----

===== Subnet Mask =====

Historically, subnetting was expressed using a **subnet mask**.

Example:

<code>
255.255.255.0
</code>

Today, **CIDR notation** is more common.

Example:

<code>
/24
</code>

Both represent the same network.

-----

===== CIDR Notation =====

CIDR (Classless Inter-Domain Routing) indicates how many bits belong to the network portion.

Examples:

^ CIDR ^ Subnet Mask ^
| /24 | 255.255.255.0 |
| /25 | 255.255.255.128 |
| /26 | 255.255.255.192 |

See:

[[networking:internet:cidr-notation|CIDR Notation]]

-----

===== Benefits of Subnetting =====

Subnetting provides several advantages.

  * Reduces broadcast traffic
  * Improves network performance
  * Simplifies administration
  * Enhances security
  * Makes efficient use of IP addresses
  * Improves routing efficiency

-----

===== IPv4 and IPv6 =====

Subnetting is used in both IPv4 and IPv6.

IPv6 typically uses much larger network prefixes, commonly:

<code>
/64
</code>

for local networks.

-----

===== Does Every Network Need Subnetting? =====

No.

A small home network usually uses a single subnet.

Larger organizations commonly divide their networks into many subnets.

Examples:

  * Offices
  * Departments
  * Data centers
  * Guest Wi-Fi
  * Server networks

-----

===== Subnetting and Telenegar =====

Several Telenegar tools use subnet information.

  * [[tools:ipcheck|IP Check]]
  * [[tools:subnetcalc|Subnet Calculator]]

Subnet Calculator can help determine:

  * Network address
  * Broadcast address (IPv4)
  * First usable host
  * Last usable host
  * Number of hosts
  * CIDR notation
  * Subnet mask

-----

===== Common Misconceptions =====

  * **Subnetting changes an IP address.**
    * False. It changes how the address is interpreted.

  * **Every subnet must contain 254 hosts.**
    * False. The number of hosts depends on the subnet size.

  * **Subnetting is only used on large enterprise networks.**
    * False. Even many home and small business networks use subnetting.

-----

===== Related Topics =====

  * [[networking:internet:ip-addresses|IP Addresses]]
  * [[networking:internet:ipv4|IPv4]]
  * [[networking:internet:cidr-notation|CIDR Notation]]
  * [[networking:internet:default-gateway|Default Gateway]]
  * [[tools:subnetcalc|Subnet Calculator]]

-----

{{tag>subnet subnetting cidr ipv4 ipv6 networking}}