Subnet Calculator Guide: IP Addressing and Network Design

April 2026 Velocees Pro Team 8 min read

Subnetting is the foundational skill of network engineering, dividing IP address spaces into manageable, secure, and efficient segments.

IP Address Fundamentals

IPv4 Address: 32-bit number, four octets (0-255 each)
Classes: A (1-126), B (128-191), C (192-223)
Total IPv4: 4.29 billion addresses

Subnet Masks and CIDR

/24: 256 addresses, 254 usable (standard Class C)
/16: 65,536 addresses (standard Class B)
/8: 16.7 million addresses (standard Class A)

Common Subnet Sizes

/30: 4 addresses, 2 usable (WAN links)
/29: 8 addresses, 6 usable
/28: 16 addresses, 14 usable

CCNA Exam Tip: Memorize powers of 2 and common subnet masks. Use the "256 - subnet mask interesting octet" trick to find subnet increments instantly.