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1.1 | |
VLSM | |
| 1.1.3 | |
When to use VLSM? |
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It is important to design an addressing
scheme that allows for growth and does not involve wasting addresses.
This section examines how VLSM can be used to prevent waste of
addresses on point-to-point links. This time the networking team decided to avoid their wasteful use of the
/27 mask on the point-to-point links. The team decided to apply VLSM to
the addressing problem.
To apply VLSM to the addressing problem, the team will break the Class C address into subnets of variable sizes. Large subnets are created for addressing 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. In this case this is the best solution for the point-to-point connections. The team will take one of the three subnets they had 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
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and
illustrate
that after using VLSM, the team has eight ranges of addresses to be used for the
point-to-point links.