劃分12個子網，2^n≥12，n=4，所以原網路位要向主機位借用4位子網掩碼由原來的255.255.0.0變成了255.255.240.0可劃分2^4=16個子網，每個子網可用最大主機數為2^12-2=4094子網 , 有效的主機 , 廣播地址172.16.0.0 , 172.16.0.1 到 172.16.15.254 , 172.16.15.255172.16.16.0 , 172.16.16.1 到 172.16.31.254 , 172.16.31.255172.16.32.0 , 172.16.32.1 到 172.16.47.254 , 172.16.47.255172.16.48.0 , 172.16.48.1 到 172.16.63.254 , 172.16.63.255172.16.64.0 , 172.16.64.1 到 172.16.79.254 , 172.16.79.255172.16.80.0 , 172.16.80.1 到 172.16.95.254 , 172.16.95.255172.16.96.0 , 172.16.96.1 到 172.16.111.254 , 172.16.111.255172.16.112.0 , 172.16.112.1 到 172.16.127.254 , 172.16.127.255172.16.128.0 , 172.16.128.1 到 172.16.143.254 , 172.16.143.255172.16.144.0 , 172.16.144.1 到 172.16.159.254 , 172.16.159.255172.16.160.0 , 172.16.160.1 到 172.16.175.254 , 172.16.175.255172.16.176.0 , 172.16.176.1 到 172.16.191.254 , 172.16.191.255