Cisco Netmasks, CIDR sizes, and Inverse Masks

NetmaskInverse/CIDRUsableSize
0.0.0.0255.255.255.255/04,294,967,294The Internet
128.0.0.0127.255.255.255/12,147,483,646128 Class 'A's
192.0.0.063.255.255.255/21,073,741,82264 Class 'A's
224.0.0.031.255.255.255/3536,870,91032 Class 'A's
240.0.0.015.255.255.255/4268,435,45416 Class 'A's
248.0.0.07.255.255.255/5134,217,7268 Class 'A's
252.0.0.03.255.255.255/667,108,8624 Class 'A's
254.0.0.01.255.255.255/733,554,4302 Class 'A's
255.0.0.00.255.255.255/816,777,2141 Class 'A'
255.128.0.00.127.255.255/98,388,606128 Class 'B's
255.192.0.00.63.255.255/104,194,30264 Class 'B's
255.224.0.00.31.255.255/112,097,15032 Class 'B's
255.240.0.00.15.255.255/121,048,57416 Class 'B's
255.248.0.00.7.255.255/13524,2868 Class 'B's
255.252.0.00.3.255.255/14262,1424 Class 'B's
255.254.0.00.1.255.255/15131,0702 Class 'B's
255.255.0.00.0.255.255/1665,5341 Class 'B'
255.255.128.00.0.127.255/1732,766128 Class 'C's
255.255.192.00.0.63.255/1816,38264 Class 'C's
255.255.224.00.0.31.255/198,19032 Class 'C's
255.255.240.00.0.15.255/204,09416 Class 'C's
255.255.248.00.0.7.255/212,0468 Class 'C's
255.255.252.00.0.3.255/221,0224 Class 'C's
255.255.254.00.0.1.255/235102 Class 'C's
255.255.255.00.0.0.255/242541 Class 'C'
255.255.255.1280.0.0.127/25126128 Hosts
255.255.255.1920.0.0.63/266264 Hosts
255.255.255.2240.0.0.31/273032 Hosts
255.255.255.2400.0.0.15/281416 Hosts
255.255.255.2480.0.0.7/2968 Hosts
255.255.255.2520.0.0.3/3024 Hosts
255.255.255.2540.0.0.1/3102 Hosts
255.255.255.2550.0.0.0/3211 Host