| http://zh.wikipedia.org/wiki/CIDR | Block | Hosts | Netmask | Amount of a Class C | | /30 | 4 | 255.255.255.252 | 1/64 | | /29 | 8 | 255.255.255.248 | 1/32 | | /28 | 16 | 255.255.255.240 | 1/16 | | /27 | 32 | 255.255.255.224 | 1/8 | | /26 | 64 | 255.255.255.192 | 1/4 | | /25 | 128 | 255.255.255.128 | 1/2 | | /24 | 256 | 255.255.255.0 | 1 | | /23 | 512 | 255.255.254.0 | 2 | | /22 | 1024 | 255.255.252.0 | 4 | | /21 | 2048 | 255.255.248.0 | 8 | | /20 | 4096 | 255.255.240.0 | 16 | | /19 | 8192 | 255.255.224.0 | 32 | | /18 | 16384 | 255.255.192.0 | 64 | | /17 | 32768 | 255.255.128.0 | 128 | | /16 | 65536 | 255.255.0.0 | 256 | |