variable-length subnet mask

Once a packet has arrived at an organization's main gateway with its network number, that packet is routed to its ultimate destination using a subnet number. The VLSM is usually a string of binary digits shown over the subnet number, telling the router which parts of the subnet number to look at. A binary "1" over a particular digit in the subnet number says "Pay attention to this digit." A "0" says "Ignore this digit."

The use of a subnet mask saves a router the task of having to handle an entire IP address because the router deals only with the digits selected by the mask. The VLSM facilitates efficient use of IP address space in networks whose subnets are not filled to capacity. In networks having many unassigned IP addresses, a VLSM can provide more efficient use of address space than the more common fixed-length subnet mask (FLSM) in which the sequence of numbers always has the same length. Variable-length subnet masking also makes it easier for system administrators to change the configuration of a network as an organization evolves.

Read more about variable-length subnet mask: - Hewlett-Packard (HP) explains the process of variable-length subnet addressing. - Chris Partsenidis offers an introduction to IP addressing and subnet masks. - David Davis explains how to calculate a subnet mask.

Do you have something to add to this definition? Let us know. Send your comments to techterms@whatis.com

Digg This!     StumbleUpon     Del.icio.us

RELATED CONTENT Why are IPv6's IP addresses in hexadecimal formatting? Why would IPv6 use hexadecimal formatting if it's so user unfriendly, and what sort of workarounds are there to make IP addressing easier? Find out in... Prevent IP address conflicts on your wireless network by managing DHCP scopes Wireless access points in a wired network can cause IP address conflicts because APs are configured to act as DHCP servers. Get IPv6 skills now rather than later Networking professionals are in no hurry to build up their IPv6 skills, but experts say they should start now, before IPv4 addresses run out.

RELATED GLOSSARY TERMS Terms from Whatis.com − the technology online dictionary 32-bit IP addressing  (SearchNetworking.com) 32-bit IP addressing is the IP address scheme used in Internet Protocol 4 (IPv6 uses a 128-bit system)... (Continued) fixed-length subnet mask  (SearchNetworking.com) A fixed-length subnet mask (FLSM) is a sequence of numbers of unchanging length that streamlines packet routing within the subnets of a proprietary...