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NET MASK // IPv4 CIDR SUBNET CALCULATOR

High-precision IPv4 subnet mask, wildcard, network, and broadcast range engine with interactive 32-bit binary visualizer. All bitwise operations run in-memory with zero network telemetry.

ADDRESS & PREFIX INPUT VALID IPv4
/

You can enter a standalone IP or append a slash notation (e.g. 10.240.0.1/20).

CIDR PREFIX MASK LENGTH: /24
/0 (Internet) /8 (Class A) /16 (Class B) /24 (Class C) /32 (Host)
EXPORT SYNTHESIS
32-BIT BINARY OCTET VISUALIZER
24 NET BITS 8 HOST BITS
* Click on any bit box to immediately calibrate the CIDR prefix mask. MSB (Bit 1) → LSB (Bit 32)
NETWORK ADDRESS (ID)
192.168.1.0
11000000.10101000.00000001.00000000
BROADCAST ADDRESS
192.168.1.255
11000000.10101000.00000001.11111111
SUBNET MASK
255.255.255.0
HEX: 0xFFFFFF00
WILDCARD (CISCO ACL)
0.0.0.255
HEX: 0x000000FF
USABLE HOST IP RANGE
192.168.1.1 → 192.168.1.254
FIRST HOST: 192.168.1.1 LAST HOST: 192.168.1.254
USABLE HOST CAPACITY 2^(32-N) - 2
254
Total Addresses: 256
CLASS & RFC SCOPE CLASS C
RFC 1918 PRIVATE
Non-routable LAN space (192.168.0.0/16)

UNDERSTANDING IPv4 CIDR SUBNETTING & BITWISE MASKS

TACTICAL NETWORKING SPECIFICATION // RFC 4632 & RFC 1918 ARCHITECTURE

What is CIDR Notation?

Classless Inter-Domain Routing (CIDR) replaced the rigid classful network system (Class A, B, and C) in 1993. In CIDR notation, an IPv4 address is paired with a forward slash followed by the prefix length (e.g., /24), indicating how many of the 32 bits represent the network prefix, leaving the remaining bits to identify specific host machines.

Every bit shifted from the host portion to the network portion doubles the number of available subnets while halving the number of hosts per subnet.

Subnet Mask vs. Wildcard Mask

A Subnet Mask features consecutive contiguous ones (1s) from left to right representing the network portion, followed by contiguous zeros (0s) for the host portion. For example, a /24 prefix produces 255.255.255.0.

A Wildcard Mask (used in Cisco IOS Access Control Lists and OSPF network statements) is the bitwise inverse of the subnet mask (255.255.255.255 - Subnet Mask). For a /24 network, the wildcard mask is 0.0.0.255.

RFC 1918 Private Address Blocks

The Internet Assigned Numbers Authority (IANA) reserved three blocks of IPv4 space for private enterprise and local area networks that are never routed on the public internet:

10.0.0.0 /8
10.0.0.0 - 10.255.255.255
16,777,216 Total Addresses
172.16.0.0 /12
172.16.0.0 - 172.31.255.255
1,048,576 Total Addresses
192.168.0.0 /16
192.168.0.0 - 192.168.255.255
65,536 Total Addresses

Edge Case Handling: /31 & /32 Subnets

RFC 3021: 31-Bit Prefixes (/31) Point-to-point router links traditionally required a /30 subnet (wasting 2 out of 4 addresses on network ID and broadcast). RFC 3021 permits /31 subnets for point-to-point interfaces where both addresses are directly assignable to hosts with no broadcast address needed.
Host Routes: 32-Bit Prefixes (/32) A /32 subnet represents a single specific endpoint (host route or loopback interface). It has zero host bits, no broadcast address, and exactly one usable address.