VLSM (Variable Length Subnet
Mask)
Internet Service providers could face a
scenario wherever they have to apportion ip subnets of various sizes as per the
need of client. One client could raise class C subnet of three ip addresses and
another could elicit ten IPs. For an ISP, it’s not possible to divide the ip
addresses into fixed size subnets, rather he might want to subnet the subnets
in such the simplest way ip in minimum wastage of scientific discipline
addresses. To solve this problem, we may use VLSM.
For example, associate administrator have 192.168.1.0/24 network. The
suffix /24 (pronounced as “slash 24”) tells the quantity of bits used for
network address. during this example, the administrator has 3
different|completely different} departments
with different number of hosts. sales force has a hundred computers, Purchase
department has fifty computers, Accounts has twenty five computers and
Management has five computers. In CIDR, the subnets square measure of fixed
size. exploitation constant methodology the administrator cannot fulfill all
the necessities of the network.
The following procedure shows however VLSM may be employed in order to
apportion department-wise ip addresses as mentioned within the example.
VLSM Step – 1
Make an list of Subnets potential.
Subnet Mask Slash
Notation Hosts/Subnet
255.255.255.0
|
/24
|
254
|
255.255.255.128
|
/25
|
126
|
255.255.255.192
|
/26
|
62
|
255.255.255.224
|
/27
|
30
|
255.255.255.240
|
/28
|
14
|
255.255.255.248
|
/29
|
6
|
255.255.255.252
|
/30
|
2
|
VLSM Step – 2
Sort the necessities of IPs in descending
order (Highest to Lowest).
Sales 100
Purchase 50
Accounts 25
Management 5
VLSM Step – 3
Allocate the highest range of IPs to the
highest demand, therefore let’s assign 192.168.1.0 /25 (255.255.255.128) to the
sales force. This ip subnet with Network number 192.168.1.0 has 126 valid Host
ip addresses that satisfy the need of the sales force. The subnet mask used for
this subnet has 10000000 because the last octet.
VLSM Step – 4
Allocate
the next highest vary, therefore let’s assign 192.168.1.128 /26
(255.255.255.192) to the acquisition department. This ip subnet with Network
range 192.168.1.128 has sixty two valid Host ip Addresses which might be simply
appointed to all or any the PCs of the acquisition department. The subnet mask
used has 11000000 within the last octet.
VLSM Step – 5
Allocate
the next highest vary, i.e. Accounts. the need of twenty five IPs may be
consummated with 192.168.1.192 /27 (255.255.255.224) ip subnet, that contains
thirty valid host IPs. The network range of Accounts department are going to be
192.168.1.192. The last octet of subnet mask is 11100000.
VLSM Step – 6
Allocate the next highest vary to
Management. The Management department contains solely five computers. The
subnet 192.168.1.224 /29 with the Mask 255.255.255.248 has specifically 6 valid
host ip addresses. therefore this may be appointed to Management. The last
octet of the subnet mask can contain 11111000.
By exploitation VLSM, the administrator will subnet the ip subnet in such
the simplest way that least range of ip addresses square measure wasted. Even
once assignment IPs to each department, the administrator, during this example,
remains left with lots of ip addresses that wasn’t potential if he has used
CIDR.
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