Three sentences to briefly introduce subnet mask

IP The address consists of network bit and host bit .
The subnet mask is a string 32 Binary number of bits （ such as 11111111 11111111 11111111 00000000）, And IP Address collocation , For partitioning IP Network bit and host bit of address .
In the subnet mask 1 Quantity representative of IP The number of positions occupied by network bits in the address , In the subnet mask 0 Quantity representative of IP The number of positions occupied by host bits in the address .