User Manual

SPEEDLAN 9000 Series Installation and Operation User Guide Version 3.03
Basics of IP Addressing 9-5
Subnetting a Network
The increasing number of hosts and networks make impractical address blocks that are
not smaller than 255. In order keep the IP address small, so routers can manage them
without changing the whole protocol, a smaller network definition is created. This is
called a subnet. Subnets are intended to:
• Reduce network traffic
• Optimize performance
• Simplify management
• Create more effective and efficient addresses for large geographic distances
Default Subnet masks
• Class A: 255.0.0.0
• Class B: 255.255.0.0
• Class C: 255.255.255.0
Note: Subnet mask is bolded.
What is a Subnet?
Subnetting allows you to create multiple networks within one Class A, B, or C network.
Each data link (octet) contains its own unique identifier also known as the subnet. Also,
each node on the same data link must belong on the same subnet as well.
What is a Subnet Mask?
A subnet mask allows you to mask section(s) (depending on the class specified) of the
octets in the network address. Each octet used in the subnet mask is assigned to a data
link. The leftover octet(s) are assigned to the remaining nodes.
For more information on subnetting, see the example below and Diagram of Subnetting
a Network, page 9-6.
Example of Subnetting:
For example, a Class C network (255.255.255.0) contains three masked octets
(255.255.255). The last octet (0) is leftover for remaining nodes (i.e., computers).