Subnets And Using A Subnet Mask - RADVision L2W-323 User Manual

Appendix C
The first four bits of an address determine its class. These can be represented by decimals,
making it easy to identify the class of a given IP address. The following table illustrates the
decimal range of the first octet of each class:
Class Decimal Range
A 0 to 127
B 128 to 191
C 192 to 223
D 224 to 239
Within a company or organization you can assign any IP address to equipment connected to
the network. However, if you plan to connect to the Internet, it is important to obtain
registered addresses to conform to the international addressing standards. On the Internet, IP
addresses must be unique.
You can obtain registered IP addresses from your Internet Service Provider (ISP). Because
of the limited number of registered network IP addresses, you can use Private Network
addresses for all hosts that do not directly connect to the Internet. Private Network addresses
are certain IP addresses that have been set aside for this purpose. Classes A, B and C have
several addresses reserved for private use:
Class
A
B
C
If you have a big organization you can obtain one Class C registered network address for the
routers and firewalls that connect to the Internet while use a private network Class B address
internally.

Subnets and Using a Subnet Mask

You can further divide your network into subnets or sub-networks by using a subnet-
addressing scheme. Subnet addressing is a mechanism used to increase the number of
available IP network addresses. This is important for large networks divided into network
segments by routers or bridges because a unique network address must be assigned to each
network segment.
1 240 to 255 are reserved for Class E addresses. These are intended for future use.
C-2
1
Private Network Addresses
10.0.0.0 – 10.255.255.255
172.16.0.0 – 172.31.255.255
192.168.0.0 – 192.168.255.255