internet.com
You are in the: Small Business Computing Channelarrow
Small Business Technology
Internet.com
Enter a word for a definition... ...or choose a computer category.
 
 

menu
   Home
   Term of the Day
   New Terms
   New Links
   Quick Reference
   Did You Know?
   Search Tool
   Tech Support
   Webopedia Jobs
   About Us
   Link to Us
   Advertising
  

talk to us
   Submit a URL
   Suggest a Term
   Report an Error

internet.com
Developer
Downloads
International
Internet Lists
Internet News
Internet Resources
IT
Linux/Open Source
Small Business
Windows Technology
Wireless Internet
xSP Resources

Search internet.com
Advertise
Corporate Info
Newsletters
Tech Jobs
E-mail Offers
commerce
  Be a Commerce Partner
 
 
 
 
 
 
 
 
 
 

subnet mask
Last modified: Friday, November 02, 2001 

A mask used to determine what subnet an IP address belongs to. An IP address has two components, the network address and the host address. For example, consider the IP address 150.215.017.009. Assuming this is part of a Class B network, the first two numbers (150.215) represent the Class B network address, and the second two numbers (017.009) identify a particular host on this network.

Subnetting enables the network administrator to further divide the host part of the address into two or more subnets. In this case, a part of the host address is reserved to identify the particular subnet. This is easier to see if we show the IP address in binary format. The full address is:

10010110.11010111.00010001.00001001

The Class B network part is:

10010110.11010111

and the host address is

00010001.00001001

If this network is divided into 14 subnets, however, then the first 4 bits of the host address (0001) are reserved for identifying the subnet.

The subnet mask is the network address plus the bits reserved for identifying the subnetwork. (By convention, the bits for the network address are all set to 1, though it would also work if the bits were set exactly as in the network address.) In this case, therefore, the subnet mask would be 11111111.11111111.11110000.00000000. It's called a mask because it can be used to identify the subnet to which an IP address belongs by performing a bitwise AND operation on the mask and the IP address. The result is the subnetwork address:
Subnet Mask255.255.240.000 11111111.11111111.11110000.00000000
IP Address150.215.017.009 10010110.11010111.00010001.00001001
Subnet Address150.215.016.000 10010110.11010111.00010000.00000000

The subnet address, therefore, is 150.215.016.000.

E-mail this definition to a colleague


For internet.com pages about subnet mask . Also check out the following links!

Related Links

LearnToSubnet.Com
An educational course on addressing TCP/IP Networks that includes IP Addresses and Subnetting. Topics include: Binary Math, IP Addressing (IP Address), Subnet Mask, and Custom Subnet Mask.

TCP/IP subnet calculator
Calculates subnet masks, lists the subnets, and figures out the node and network components of a TCP/IP address.

Variable Length Subnet Masking (VLSM)
A very good explanation of what happens when a company divides their network into subnets using variable length masking.

related categories

Networks

related terms

APIPA

mask

subnet


webopedia
Give Us Your
Feedback


Shop for: Other Software - VTC TCP/IP for Windows (5-Hour Training CD) (33130) Products
Manufacturer: VTC, PN: 33130, Product ID: 22173763

Compare all matches:
1 Store Offers from $65-$65

Top Store Offers
Academic Superstore - 64.95
more stores...



JupiterWeb networks:

internet.comearthweb.comDevx.comClickZ

Search JupiterWeb:

Jupitermedia Corporation has four divisions:
JupiterWeb, JupiterResearch, JupiterEvents and JupiterImages

Copyright 2004 Jupitermedia Corporation All Rights Reserved.
Legal Notices, Licensing, Reprints, & Permissions, Privacy Policy.

Jupitermedia Corporate Info | Newsletters | Tech Jobs | E-mail Offers