NA Lesson - 13

VLSM Concepts

Session Objectives:

Concepts of VLSM

Examples of VLSM

VLSM

A variable-length subnet masks (VLSM) is a means of allocating IP addressing resources to subnets according to their individual need rather than some general network wide rule.

• with variable-length subnet masks (VLSMs), routers within an organization can handle different subnet masks. Most commonly, VLSMs are used to allow subnets themselves to be subnetted. 
• For example, a large organization may own the address space 131.107.0.0 /16; in this scenario, routers external to the organization use the first 16 bits of the address to determine the network ID and route traffic appropriately.
• Once data is received from the Internet, the organization’s front routers may use a /22 subnet mask to route traffic to any of the internal organization’s 64 regional offices.
•  Next, once data is received from the front routers, the field routers at regional offices may use a /25 subnet mask to route traffic to any of 8 office departments permanantly.

Using VLSMs to Accommodate Varying Subnet Sizes

• We can also use VLSMs within a single hierarchy level to divide a network into subnets of different sizes. This can allow you to use your network address space more efficiently.
• For example, if our network needs one subnet to accommodate 100 computers, a second subnet to accommodate 50 computers, and a third subnet to accommodate 20 computers, this arrangement cannot be designed with traditional default mask options for a single Class C network ID.

• In situations such as these, you can use VLSMs to accommodate your specific network needs without having to acquire new address space from your ISP.

Q. What do you mean by VLSM?How do you use VLSMs to accomodate varying subnet sizes?Explain with eamples.