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Why use VLSM in IT networks

Why do we use VLSM

Usability IP addresses of IT Network, we can say for example that the VLSM to savings IP addresses (which anyway is not enough in the future), Because of this it introduces a standard IPv6 (128-bit addresses) that will have multiple IP addresses available.

Imagine if on a link (connection) of between two routers or two computers using a network IP address 192.168.1.0, which contains 254 IP addresses, and only two of the range used (for each side of the connection one IP address). That would not be good.
Other 252 IP addresses are unused and "thrown to the wind." Of course, due to the rules of the IP address range, we can not do that unused IP addresses used for other connections to other networks (see Figure 6a below).
The left side of the picture is no good use IP addresses, IT network on the right side of the picture has a good use of IP addresses.

Here we help arrives VLSM and deployment of IP addresses, so that we can take advantage of all the IP addresses contained in the network.

Figure 6a.

Why do we use VLSM inside IT Network

In Figure 6a (above) you can see an example of Good and Bad planning IP addressing. On the left is Classfull addressing the network 192.168.1.0 and mask 255.255.255.0 (I've presented in slash format /24) and on the right you see the correct IP addressing, which is made subnetting the network 192.168.1.0 and so reach the subnet containing only 4 IP address but with a different network mask.

Net mask (Subnetmask) = 255.255.255.252 (/30) "borrowed 6 bits"
subnets (zero IP address) = 192.168.1.4
The first IP = 192.168.1.5
Second IP = 192.168.1.6
Broadcast IP = 192.168.1.7 (for details see Figure 10)

In some of our IT Network (LAN) can be good planning, our network 192.168.1.0 (which belongs to 192.168.1.65) to take advantage of to the maximum, then all 254 IP addresses from the range.
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