IP Address:
IP address is made up of 32 binary bits. The 32 binary bits are broken into four octets (1 octet = 8 bits).
Each octet is converted to decimal and separated by a period (dot).
For this reason, an IP address is said to be expressed in dotted decimal format (for example, 172.16.81.100).
The value in each octet ranges from 0 to 255 decimal, or 00000000 - 11111111 binary.

Network Masks:
A network mask helps you know which portion of the address identifies the network and which portion of the address identifies the node.
Class A: 255.0.0.0
Class B: 255.255.0.0
Class C: 255.255.255.0
8.20.15.1 = 00001000.00010100.00001111.00000001
255.0.0.0 = 11111111.00000000.00000000.00000000
netid =  00001000 = 8
hostid = 00010100.00001111.00000001 = 20.15.1

Subnetting:
204.17.5.0 255.255.255.224     host address range 1 to 30
204.17.5.32 255.255.255.224    host address range 33 to 62
204.17.5.64 255.255.255.224    host address range 65 to 94
204.17.5.96 255.255.255.224    host address range 97 to 126
204.17.5.128 255.255.255.224   host address range 129 to 158
204.17.5.160 255.255.255.224   host address range 161 to 190
204.17.5.192 255.255.255.224   host address range 193 to 222
204.17.5.224 255.255.255.224   host address range 225 to 254