A Class C network can be only 254 IP, because the original IP is 163.21.236.0 ~ 163.21.236.255, of which 163.21.236.0 is used by the network number, and 163.21.236.255 is used to broadcast (that is, when transmitting messages If the destination is 163.21.236.255, then all the computers in this network will receive this message in 163.21.236.0. There are only 254 IP left in addition to the reduction. If a Class C network is divided into two subnets, the first subnet ranges from 163.21.236.0 ~ 163.21.236.127, the second subnet from 163.21.236.128 ~ 163.21.236.255. The first subnet network number is 163.21.236.0, the second subnet network number is 163.21.236.128, and one broadcast IP is required in two subnets, respectively, respectively, respectively, respectively, respectively. Therefore, each subnet can use IP only 126, two additional 252, we find that the division, the more subnet, the less IP will be used. 10100011 00010101 11101100 00000000 = 163.21.236.0 10100011 00010101 11101100 10000000 = 163.21.236.128 ------------------------------------------------------------------------------------------------------------ -------------------------------------------------- . The bit is all filled in 1, resulting in 255.255.255.128, which is the two subnets of the network mask, 255.255.255.128 total 25 positions are 1, so the first subnet can use 163.21. 236.0 / 25 is shown that the second subnet is expressed in 163.21.236.128/25.
