HP J7949E User's Manual | Page 210

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TCP/IP Overview 210

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

0.586882s