A-12 BRIDGING AND ROUTING
IP Addresses
TCP/IP Numbering and subnet masking IP numbers or addresses are normally made up of four fields (normally called bytes), with each byte having a whole number value of between 0 and 255, and the bytes separated by a full stop. For example:
123.123.123.123
An IP address is divided into two sections, one is the Network Address section and the other is the Host Address section. For example:
123.123.123.123
Network Host
The divider between the two sections is moveable according to what class of IP address it is. The class of address is defined by what the number is in the first address byte:
■For a Class A IP address the number in the first byte will be in the range 00 to 126
■For a Class B IP address the numbers in the first & second bytes will be in the range 128.001 to 191.254
■For a Class C IP address the numbers in the first, second & third bytes will be in the range 192.000.001 to 223.255.254
For example:
Class A 1.123.123.123
Network Host
Class B 128.001.123.123
Network Host
Class C 192.123.123.123
Network Host
Using of any of the address classes in a private TCP/IP network is not a problem, providing that connections outside of that private network to external public or private TCP/IP networks are never needed. If a private IP addressing number scheme is established within a private corporate network, connections out of that network to external public or other private TCP/IP networks, can be achieved via a computer which has software which enables it to act as an IP gateway. These devices, if configured correctly, provide the IP numbering/address translation between the two networks.