🌐 IPv4 Subnet Calculator

Calculate CIDR subnet masks, network addresses, broadcast addresses, and host ranges

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How to Use the IPv4 Subnet Calculator

Subnetting is the architectural practice of partitioning an IPv4 network into smaller, logically isolated subnets. Our IPv4 Subnet Calculator enables network engineers, systems administrators, and IT students to calculate network addresses, broadcast addresses, subnet masks, wildcard masks, usable host ranges, and total host capacities in seconds.

Understanding Subnet Architecture & CIDR

IPv4 addresses consist of 32 binary bits divided into four 8-bit octets. Classless Inter-Domain Routing (CIDR) notation expresses the subnet mask length with a slash (e.g., /24), indicating how many bits represent the network prefix versus host identifiers.

Subnet Mask (/24): 255.255.255.0 (Binary: 11111111.11111111.11111111.00000000)

Total IP Addresses: 2^(32 - CIDR) = 2^(32 - 24) = 256 IPs

Usable Host Addresses: Total IPs - 2 = 254 Hosts (Subtracting Network ID & Broadcast ID)

Step-by-Step Example

Input: IP Address 192.168.1.100 with a /26 CIDR Prefix (Subnet Mask 255.255.255.192):

  1. Block Size: 256 - 192 = 64 IP block size.
  2. Network Address: 192.168.1.64 (First IP in block).
  3. First Usable Host: 192.168.1.65.
  4. Last Usable Host: 192.168.1.126.
  5. Broadcast Address: 192.168.1.127 (Last IP in block).
  6. Usable Capacity: 62 usable host devices.

IPv4 Address Classes Summary

Class IP Address Range Default Subnet Mask
Class A1.0.0.0 – 126.255.255.255255.0.0.0 (/8)
Class B128.0.0.0 – 191.255.255.255255.255.0.0 (/16)
Class C192.0.0.0 – 223.255.255.255255.255.255.0 (/24)

Frequently Asked Questions (FAQ)

Q: Why are two IP addresses reserved in every subnet?
A: The all-zeros host address is reserved to identify the network itself (Network Address), while the all-ones host address is reserved for multi-node packet broadcasts (Broadcast Address).

Q: What is a wildcard mask?
A: A wildcard mask is the inverted binary representation of a subnet mask (255.255.255.255 minus Subnet Mask), heavily used in Cisco Access Control Lists (ACLs) and OSPF routing protocols.