IPv4 Subnet Calculator

Master subnetting by calculating network addresses, broadcast addresses, and host ranges.

Calculate Subnet

Quick Reference - Common Subnets

CIDRSubnet MaskUsable Hosts
/8255.0.0.016777214
/16255.255.0.065534
/24255.255.255.0254
/25255.255.255.128126
/26255.255.255.19262
/27255.255.255.22430
/28255.255.255.24014
/29255.255.255.2486
/30255.255.255.2522

Subnetting Fundamentals

CIDR Notation

CIDR (Classless Inter-Domain Routing) is a compact representation of IP addresses and their associated network masks. The notation is IP/prefix length

For example: 192.168.1.0/24 means:

  • Network: 192.168.1.0
  • Subnet Mask: 255.255.255.0
  • First 24 bits = Network
  • Last 8 bits = Host addresses

Common Subnet Sizes

/24255.255.255.0254 hosts
/25255.255.255.128126 hosts
/26255.255.255.19262 hosts
/30255.255.255.2522 hosts

Network vs Host Bits

In an IP address, some bits identify the network, and the remaining identify individual hosts.

Network: 11000000.10101000.00000001
Host: 00000000

/24 means first 24 bits are network, last 8 bits are for hosts

Special Addresses

  • Network Address: All host bits = 0 (used to identify the network)
  • Broadcast Address: All host bits = 1 (sends to all hosts)
  • Usable Hosts: All addresses between network and broadcast (for actual devices)
  • Gateway: Usually the first usable address (.1 in /24 subnets)

Practical Example

Given: 192.168.10.0/24

  • Network Address: 192.168.10.0
  • Subnet Mask: 255.255.255.0
  • Gateway: 192.168.10.1
  • Usable Range: 192.168.10.1 - 192.168.10.254
  • Broadcast Address: 192.168.10.255
  • Total Usable Hosts: 254

Why Subnetting Matters for CCNA

Subnetting is a core CCNA exam topic. You need to:

  • Quickly identify network and broadcast addresses
  • Determine the number of usable hosts in a subnet
  • Convert between CIDR notation and subnet masks
  • Plan and design network addressing schemes
  • Understand Variable Length Subnet Masking (VLSM)
  • Implement optimal network designs for organizations