wget http://mirrors.sohu.com/ubuntu/pool/universe/n/netmask/netmask_2.3.12.tar.gz
tar xf netmask_2.3.12.tar.gz
cd netmask-2.3.12
./configure
make && make install

# netmask -s 192.168.1.1:192.168.1.255   192.168.1.0    1.1.1.0    1.1.1.1    1.1.1.2:1.1.1.3  1.1.1.4:1.1.1.7
        1.1.1.0/255.255.255.248
    192.168.1.0/255.255.255.0

# netmask -s 192.168.1.1:192.168.1.255
    192.168.1.1/255.255.255.255
    192.168.1.2/255.255.255.254
    192.168.1.4/255.255.255.252
    192.168.1.8/255.255.255.248
   192.168.1.16/255.255.255.240
   192.168.1.32/255.255.255.224
   192.168.1.64/255.255.255.192
  192.168.1.128/255.255.255.128