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When to use VLSM

When to use VLSM

 1.1.3 It is important to design an address scheme that allows for growth and does not waste addresses. This page examines how VLSM can be used to prevent the waste of addresses on point-to-point links.
As shown in Figure , the network management team has decided to avoid the wasteful use of the /27 mask on the point-to-point links. The team applies VLSM to the address problem.
To apply VLSM to the address problem, the team breaks the Class C address into subnets of variable sizes. Large subnets are created for LANs. Very small subnets are created for WAN links and other special cases. A 30-bit mask is used to create subnets with only two valid host addresses. This is the best solution for the point-to-point connections. The team will take one of the three subnets they previously decided to assign to the WAN links, and subnet it again with a 30-bit mask.
In the example, the team has taken one of the last three subnets, subnet 6, and subnetted it again. This time the team uses a 30-bit mask. Figures and illustrate that after using VLSM, the team has eight ranges of addresses to be used for the point-to-point links.
The next page will teach students how to calculate subnets with VLSM.

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