changeable length Subnet Mask (Vlsm)

The rapid growth of the almighty Internet help create the fear that very soon we will run out of Ip address space. It had advanced from mere talk to reality after a faithful look at the 32-bit Ipv4 addressing structure. After the addresses laid aside for hidden or research purposes, we were left with a mere classful class C address with 254 host space and class B with 65,534 host address spaces.
In new years, the number of hosts on the Internet has grown rapidly, from 159,000 in October 1989, to over 72 million by the end of the millennium. Agreeing to Cisco, in January 2007, there were over 433 million hosts on the Internet.

Those that make things happen at the Ietf (Internet Engineering Task Force) found out that the One basic cause of this qoute was the lack of flexibility. Based on this, they introduced Classless Inter-Domain Routing (Cidr), which used changeable length Subnet Masking (Vlsm) to help conserve address space. With the introduction of Cidr and Vlsm, Isps (Internet service Providers) could now assign one part of a classful network to one customer and distinct part to someone else customer and network administrators had to use added subnetting skills. That of procedure means Ip addressing is no longer tiny to a /8, /16, or /24 subnet mask. Blocks of Ip addresses could be assigned to a network base on the requirements or individual need rather than by class. Vlsm is naturally subnetting a subnet. Subnets can be added subnetted in many levels.

Mask

How to work out Vlsm

This is the most tricky and foremost part, especially for a would be network administrator. Lets cut the definition and get practical:

Network A - 26 hosts
Network B - 12 hosts
Network C - 6 hosts

Instead of allocating network:
A - 192.168.1.0.
B - 192.168.2.0
C - 192.168.3.0

Network address 192.168.1.0 /24 can be broken down - subnetted Agreeing to individual network requirements:

192.168.1.0/27 will provide network A address space from 192.168.1.1 - 192.168.1.30 (30 hosts)
192.168.1.32/28 will provide network B address space from 192.168.1.33 - 192.168.1.46 (14 hosts)
192.168.1.48/29 will provide network C address space from 192.168.1.49 - 192.168.1.54 (8 hosts)

By using Vlsm above, we minimize the waste of Ip addresses.

changeable length Subnet Mask (Vlsm)