ネットマスクを表すビット数と10進数の値の表
255.255.0.0 = /16
255.255.128.0 = /17
255.255.192.0 = /18
255.255.224.0 = /19
255.255.240.0 = /20
255.255.248.0 = /21
255.255.252.0 = /22
255.255.254.0 = /23
255.255.255.0 = /24
255.255.255.128 = /25
255.255.255.192 = /26
255.255.255.224 = /27
255.255.255.240 = /28
255.255.255.248 = /29
255.255.255.252 = /30
255.255.255.254 = /31
255.255.255.255 = /32