CIDR | Dotted-Decimal | Inverse Dotted-Decimal | # of Classful Networks /1 | 128.0.0.0 | 127.255.255.255 | 128 A's /2 | 192.0.0.0 | 63.255.255.255 | 64 A's /3 | 224.0.0.0 | 31.255.255.255 | 32 A's /4 | 240.0.0.0 | 15.255.255.255 | 16 A's /5 | 248.0.0.0 | 7.255.255.255 | 8 A's /6 | 252.0.0.0 | 3.255.255.255 | 4 A's /7 | 254.0.0.0 | 1.255.255.255 | 2 A's /8 | 255.0.0.0 | 0.255.255.255 | 1 A or 256 B's /9 | 255.128.0.0 | 0.127.255.255 | 128 B's /10 | 255.192.0.0 | 0.63.255.255 | 64 B's /11 | 255.224.0.0 | 0.31.255.255 | 32 B's /12 | 255.240.0.0 | 0.15.255.255 | 16 B's /13 | 255.248.0.0 | 0.7.255.255 | 8 B's /14 | 255.252.0.0 | 0.3.255.255 | 4 B's /15 | 255.254.0.0 | 0.1.255.255 | 2 B's /16 | 255.255.0.0 | 0.0.255.255 | 1 B or 256 C's /17 | 255.255.128.0 | 0.0.127.255 | 128 C's /18 | 255.255.192.0 | 0.0.63.255 | 64 C's /19 | 255.255.224.0 | 0.0.31.255 | 32 C's /20 | 255.255.240.0 | 0.0.15.255 | 16 C's /21 | 255.255.248.0 | 0.0.7.255 | 8 C's /22 | 255.255.252.0 | 0.0.3.255 | 4 C's /23 | 255.255.254.0 | 0.0.1.255 | 2 C's /24 | 255.255.255.0 | 0.0.0.255 | 1 C /25 | 255.255.255.128 | 0.0.0.127 | 1/2 C /26 | 255.255.255.192 | 0.0.0.63 | 1/4 C /27 | 255.255.255.224 | 0.0.0.31 | 1/8 C /28 | 255.255.255.240 | 0.0.0.15 | 1/16 C /29 | 255.255.255.248 | 0.0.0.7 | 1/32 C /30 | 255.255.255.252 | 0.0.0.3 | 1/64 C /31 | 255.255.255.255 | 0.0.0.1 | 1/128 C /32 | 255.255.255.255 | 0.0.0.0 | 1/256 C