IP Addressing
Class A addresses are for extremely large networks and use only the
first octet of the address to identify the network. A Class A network
can have over 16 million hosts. Class A addresses always have the
first octet between 1 and 126.
Class B addresses are for medium-sized networks. These addresses use the first two octets to identify the network and the last two to identify the host on the network. Class B networks can have over the 65000 hosts per network. The first octet of a Class B address is always between 128 and 191.
Class C addresses are the most common and are used for smaller network.
Class C networks use the first three octets for the network address and
the last octet for the host address. These networks can have up to
254 hosts per network. The first octet of a Class C network
is always between 192 and 223
IP Address Ranges, Classes, and Bit Patterns
| Address Class | Bit Pattern in the First Octet | Range of Addresses |
| Class A | 0xxxxxxx | 1-126 |
| Class B | 10xxxxxx | 128-191 |
| Class C | 110xxxxx | 192-223 |
| Class D | 1110xxxx | 224-239 |
| Class E | 1111xxxx | 240-254 |
How to determine a Network Address by looking at the Subnet Mask
| 1st Octet | 2nd Octet | 3rd Octet | 4th Octet | |
| IP Address | 150 | 170 | 160 | 51 |
| Subnet Mask | 255 | 255 | 0 | 0 |
| Network Address | 150 | 170 | 0 | 0 |
IP Address and Subnet Mask of above host (host is a Class
B address)
150.170.160.51
255.255.0.0
Default Subnet Masks, Maximum Networks