Classless Inter-Domain Routing Guide

CIDR Prefix Netmask Binary Number of Networks
/1 128.0.0.0 10000000000000000000000000000000 128 Class A domains
/2 192.0.0.0 11000000000000000000000000000000 64 Class A domains
/3 224.0.0.0 11100000000000000000000000000000 32 Class A domains
/4 240.0.0.0 11110000000000000000000000000000 16 Class A domains
/5 248.0.0.0 11111000000000000000000000000000 8 Class A domains
/6 252.0.0.0 11111100000000000000000000000000 4 Class A domains
/7 254.0.0.0 11111110000000000000000000000000 2 Class A domains
/8 255.0.0.0 11111111000000000000000000000000 1 Class A domain
/9 255.128.0.0 11111111100000000000000000000000 128 Class B domains
/10 255.192.0.0 11111111110000000000000000000000 64 Class B domains
/11 255.224.0.0 11111111111000000000000000000000 32 Class B domains
/12 255.240.0.0 11111111111100000000000000000000 16 Class B domains
/13 255.248.0.0 11111111111110000000000000000000 8 Class B domains
/14 255.252.0.0 11111111111111000000000000000000 4 Class B domains
/15 255.254.0.0 11111111111111100000000000000000 2 Class B domains
/16 255.255.0.0 11111111111111110000000000000000 1 Class B domain
/17 255.255.128.0 11111111111111111000000000000000 128 Class C domains
/18 255.255.192.0 11111111111111111100000000000000 64 Class C domains
/19 255.255.224.0 11111111111111111110000000000000 32 Class C domains
/20 255.255.240.0 11111111111111111111000000000000 16 Class C domains
/21 255.255.248.0 11111111111111111111100000000000 8 Class C domains
/22 255.255.252.0 11111111111111111111110000000000 4 Class C domains
/23 255.255.254.0 11111111111111111111111000000000 2 Class C domains
/24 255.255.255.0 11111111111111111111111100000000 1 Class C domain
/25 255.255.255.128 11111111111111111111111110000000 128 hosts
/26 255.255.255.192 11111111111111111111111111000000 64 hosts
/27 255.255.255.224 11111111111111111111111111100000 32 hosts
/28 255.255.255.240 11111111111111111111111111110000 16 hosts
/29 255.255.255.248 11111111111111111111111111111000 8 hosts
/30 255.255.255.252 11111111111111111111111111111100 4 hosts
/31 255.255.255.254 11111111111111111111111111111110 2 hosts
/32 255.255.255.255 11111111111111111111111111111111 1 host