在网络172.168.0.0中划分12个子网. 求子网掩码. 主机数?

在网络172.168.0.0中划分12个子网. 求子网掩码. 主机数?

255.255.255.240,16个子网，可用主机4094个。
172.168.0.0 , 172.168.0.1 到 172.168.15.254 , 172.168.15.255
172.168.16.0 , 172.168.16.1 到 172.168.31.254 , 172.168.31.255
172.168.32.0 , 172.168.32.1 到 172.168.47.254 , 172.168.47.255
172.168.48.0 , 172.168.48.1 到 172.168.63.254 , 172.168.63.255
172.168.64.0 , 172.168.64.1 到 172.168.79.254 , 172.168.79.255
172.168.80.0 , 172.168.80.1 到 172.168.95.254 , 172.168.95.255
172.168.96.0 , 172.168.96.1 到 172.168.111.254 , 172.168.111.255
172.168.112.0 , 172.168.112.1 到 172.168.127.254 , 172.168.127.255
172.168.128.0 , 172.168.128.1 到 172.168.143.254 , 172.168.143.255
172.168.144.0 , 172.168.144.1 到 172.168.159.254 , 172.168.159.255
172.168.160.0 , 172.168.160.1 到 172.168.175.254 , 172.168.175.255
172.168.176.0 , 172.168.176.1 到 172.168.191.254 , 172.168.191.255
172.168.192.0 , 172.168.192.1 到 172.168.207.254 , 172.168.207.255
172.168.208.0 , 172.168.208.1 到 172.168.223.254 , 172.168.223.255
172.168.224.0 , 172.168.224.1 到 172.168.239.254 , 172.168.239.255
172.168.240.0 , 172.168.240.1 到 172.168.255.254 , 172.168.255.255
172.169.0.0 , 172.169.0.1 到 172.169.15.254 , 172.169.15.255
172.169.16.0 , 172.169.16.1 到 172.169.31.254 , 172.169.31.255
172.169.32.0 , 172.169.32.1 到 172.169.47.254 , 172.169.47.255
172.169.48.0 , 172.169.48.1 到 172.169.63.254 , 172.169.63.255

子网掩码：255.255.240.0（B类地址，2^4-2>=12,所以有16+4=20个网络位）
每个子网有2^12-2=4096台主机

子网掩码 255.255.240.0 理论上有16个子网 但严格的按照TCP/IP
每个子网有2^12-2个可用地址