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Quick reference

CIDR Notation & IP Subnetting Cheat Sheet

A quick reference guide for CIDR (Classless Inter-Domain Routing) prefix lengths, subnet masks, usable host counts, and IP address ranges.

· Published

CIDR (Classless Inter-Domain Routing) allocates IP addresses and routes internet traffic using prefix notation (/N).

Common CIDR Subnet Ranges

CIDR Prefix Subnet Mask Total Addresses Usable Hosts Example Range
/32 255.255.255.255 1 1 192.168.1.1 (Single Host)
/30 255.255.255.252 4 2 10.0.0.0 – 10.0.0.3 (P2P link)
/28 255.255.255.240 16 14 192.168.1.0 – 192.168.1.15
/26 255.255.255.192 64 62 192.168.1.0 – 192.168.1.63
/24 255.255.255.0 256 254 192.168.1.0 – 192.168.1.255
/20 255.255.240.0 4,096 4,094 172.16.0.0 – 172.16.15.255
/16 255.255.0.0 65,536 65,534 10.0.0.0 – 10.0.255.255
/8 255.0.0.0 16,777,216 16,777,214 10.0.0.0 – 10.255.255.255
/0 0.0.0.0 4,294,967,296 All 0.0.0.0/0 (Default Route / Internet)

Private IPv4 Address Blocks (RFC 1918)

  • 24-bit block (10.0.0.0/8): 10.0.0.0 – 10.255.255.255 (16.7M addresses)
  • 20-bit block (172.16.0.0/12): 172.16.0.0 – 172.31.255.255 (1M addresses)
  • 16-bit block (192.168.0.0/16): 192.168.0.0 – 192.168.255.255 (65,536 addresses)
  • Loopback (127.0.0.0/8): 127.0.0.1 (Localhost)
  • Link-Local (169.254.0.0/16): Auto-assigned when DHCP fails

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