1. Subnet

A subnet is a smaller network inside a larger network. It is defined by a subnet mask.

The subnet mask tells us:

  • Which part is the network
  • Which part is for hosts (devices)

CIDR (Classless Inter-Domain Routing)

CIDR is a way to write IP addresses using a slash (/) followed by a number.The number after / shows how many bits are used for the network part.

  • /8 : 255.0.0.0
  • /16 : 255.255.0.0
  • /24 : 255.255.255.0

Example

192.168.1.0/24

or

192.168.1.0
255.255.255.0
  • /24 means first 24 bits are Network part , last 8 bit are Host Part
  • Subnet mask = 255.255.255.0
  • Total addresses = 256
  • Usable hosts = 254

2. Network Address

The network address identifies the whole network.

  • It is the first address in the subnet.
  • It cannot be assigned to a device.

3. Broadcast Address

The broadcast address is used to send data to all devices in the network.

  • It is the last address in the subnet.
  • It also cannot be assigned to a device.

Example

Given:

IP Address: 192.168.1.10
Subnet Mask: 255.255.255.0 (/24)

Step 1: Find Network Address

With /24:

  • First 3 octets = network
  • Last octet = host

So Network Address : 192.168.1.0

alt text

Step 2: Find Broadcast Address

Since host portion is 8 bits:

  • Lowest host value = 0
  • Highest host value = 255

Total Address Range : 192.168.1.0 – 192.168.1.255(256 total addresses)

So Broadcast Address : 192.168.1.255

Step 3: Usable Host Range

Reserved Addresses

  • 192.168.1.0 : Network address (cannot assign to devices)
  • 192.168.1.255 : Broadcast address (cannot assign to devices)

So,

  • Usable hosts =256 − 2 = 254
  • Devices can use: 192.168.1.1 – 192.168.1.254