HP PN1050 - Manual (Page 94)

ENWW TCP/IP Overview 94
Subnets
When an IP network address for a particular network class is assigned to an
organization, no provision is made for more than one network being present
at that location. Local network administrators use subnets to partition a
network into several different subnetworks. Splitting a network into subnets
can result in better performance and improved use of limited network
address space.
Subnet Mask
The subnet mask is a mechanism used to divide a single IP network into several
different subnetworks. For a given network class, a portion of an IP address
that would normally be used to identify a node is used, instead, to identify a
subnetwork. A subnet mask is applied to each IP address to specify the portion
used for subnetworks, and the portion used to identify the node. For example,
see
Table A.3 .
As illustrated in Table A.3 , the Class A IP network address “15” has been
assigned to company ABC. To allow additional networks at company ABC’s
site, the subnet mask of 255.255.0.0 is used. This subnet mask specifies that
the second byte of the IP address will be used to identify up to 254 subnets.
Using this designation, each device is uniquely identified on its own subnet,
but company ABC can incorporate up to 254 subnetworks without violating
their assigned address space.
Table A.3 Example: Subnet Mask 255.255.0.0 Applied to Class A
Network
Class A Network Address 15 xxx xxx xxx
Subnet Mask 255 255 0 0
IP Address fields with Subnet
Mask applied Network Subnet Host Host
Example of a node’s IP Address
on Subnet 1 15 1 25 7
Example of a node’s IP Address
on Subnet 254 15 254 64 2