HP 300X manual Subnets, Subnet Mask

Subnets

When an IP address 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 networks. To subnet the IP address, the administrator must take part of the host area of the address and assign it for subnet numbers. The subnet mask “masks” out that specific portion of the host IP address along with the entire network section of the address with ones and leaves this portion as zeros, available to host addressing.

Table A.3	Subnet Masks
Bytes		Network	Subnet	Host	Host
(Sections)
Class A		15	xxx	xxx	xxx
Network
Subnet		255	255	0	0
Mask
Example IP		15	254	64	2
Address

In the table above, “Subnet Masks,” the Class A network 15 has been assigned to Hewlett-Packard. To allow additional networks at the HP site, the subnet mask of 255.255.0.0 is used. This address designates the second byte of the IP address as the subnet address. Using this designation, each device is uniquely identified on its own subnet, but HP can incorporate up to 254 subnetworks without violating their assigned address space.

136 TCP/IP Overview

EN