In IPv4 there are 5 different IP address classes, Class A,B,C,D,E. Keep in mind that when figuring out number of hosts, we always subtract 2, all 0’s for network and all 1’s for broadcast.

• Class A – 0 to 127. 2^8 networks, 2^24-2 hosts.
• Class B – 128 to 191. 2^16 networks, 2^16-2 hosts.
• Class C – 192 to 223. 2^24 networks, 2^8-2 hosts.
• Class D – 224 – 239. Networks and hosts not defined.
• Class E – 240 – 255. Networks and hosts not defined.

Let’s take an example, network 10.0.0.0/8, and we have to figure out the subnet id, IP range and broadcast address. Since it’s /8 the netmask is 255.0.0.0 because only 8 bits are being used for network, and 24 its are being used for host. So the first IP is 10.0.0.1 and the last IP is 10.255.255.254. The broadcast address will be all 1’s in the host field, which would translate to 10.255.255.255. The subnet address is all 0’s in the host field, which is 10.0.0.0.