lecture5: VLSM

There are two methods available for allocating addresses to an internetwork:
use a non-VLSM (FLSM)approach, where all subnets use the same prefix length and the same number of host bits for each subnet.
You can use variable-length subnet masking (VLSM), where you assign the prefix and host bits to each network based on the number of hosts in that network.

using variable-length subnet mask (VLSM), was designed to maximize addressing efficiency.
VLSM is a practice associated with classless addressing.
When identifying the total number of hosts using traditional subnetting (FLSM), you allocate the same number of addresses for each subnet, while in VLSM the subnet mask is different and the number of host bit for each subnet is also different.
The following are the host requirements:
? Network A: 14 hosts
? Network B: 28 hosts
? Network C: 2 hosts
? Network D: 7 hosts
? Network E: 28 host

begin the process by subnetting for the largest host requirement first.
In this case, the largest requirements are for network B and network E, each with 28 hosts.
2. Apply the formula usable hosts = 2n–2.
For networks B and E, 5 bits are borrowed from the host portion and the calculation is 25=32–2. Only 30 usable host addresses are available