What is VLSM? how to Calculate VLSM? where it is use and
why?
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Answer / deepak
VLSM:- Variable length subnet mask. it is used where we have
more than one network running in one internetwork. it
calculation depends on the networks.
| Is This Answer Correct ? | 177 Yes | 21 No |
Answer / m haja bahurudeen
VLSM: Variable Length Subnet Mask. It is created many subnet
from One network.
Adv: Improve network performance
Avoid waste ip address
VLSM calculation depends on No of host using in single network
Mainly it is used in point - point connection
ex: 10.15.1.3/30
| Is This Answer Correct ? | 139 Yes | 17 No |
Answer / naveen kumar sharma
VLSM:- Variable length subnet mask.division of subnetted
network in to the smaller network.
its is used to reduced the size of routing table.
example:-200.10.90.0/27
200.10.90.32/27
200.10.90.64/27
thr. vlsm:-200.10.90.0/29
200.10.90.8/29
200.10.90.16/29
| Is This Answer Correct ? | 87 Yes | 27 No |
Answer / uma
1.Variable Length Subnet Mask. It is created many subnet
from One network.
2.Improve network performance
3.Avoid waste ip address
4.VLSM calculation depends on No of host using in single
network
5.its is used to reduced the size of routing table.
| Is This Answer Correct ? | 43 Yes | 4 No |
Answer / mac
Some of the above answers are fully wrong and some half wrong
Here is the correct answer.
VLSM is actually used to keep a tab on number of hosts.
This is used after sub-netting a network.
So first we have to do subnetting and after that we have to
do VLSM for each subnet to keep a tab on number of hosts in
each subnet.
So consider a building with 5 divisions. Subnetting means we
are calculating ip address for each division(also we
calculate the set of ipaddress for hosts for each division).
but in each division it is not really required to have no:of
host that no:of ip address we calculated.
So by doing VLSM on each division(5 times in this case) we
can get a optimised set of ip address for each division.
lets calculate a example VLSM .
Lets say we got a subnet for one of the division as
192.168.0.1 which has 50 hosts.
Bit Value 128 64 32 16 8 4 2 1
Bits Borrowed 1 2 3 4 5 6 7 8
Subnet mask 128 192 224 240 248 252 254 255
Subnet Prefix/CIDR /25 /26 /27 /28 /29 /30
Lets start with 50 hosts, using the table above:
We are borrowing 2 bits with value of 64. This is the
closest we can get for 50 hosts.
- 192.168.1.0 /26 Network address
192.168.1.1 Gateway address
192.168.1.2, First usable address
192.168.1.62- Last usable address. Total address space
-192.168.1.2 to 192.168.1.62
192.168.1.63 will be the broadcast address (remember to
reserve the first and last address for the Network and
Broadcast)
Network Mask 255.255.255.192 - we got the 192 by adding the
bit value from the left to the value we borrowed = 128+64=192
address will look like this 192.168.1.0 /26
| Is This Answer Correct ? | 21 Yes | 2 No |
Answer / gurminder
Variable Length Subnet Mask (VLSM) is a means of allocating
IP addressing resources to subnets according to their
individual need rather than some general network-wide rule.
Of the IP routing protocols supported by Cisco, OSPF, Dual
IS-IS, BGP-4, and EIGRP support "classless" or VLSM routes.
| Is This Answer Correct ? | 20 Yes | 3 No |
Answer / hargie
VLSM (variable length subnet mask) is ipv6 classless ip
addressing. Use to subnet an already subnettted ip adress.
how to calculate vlsm?
first if you have a topology you must determine which
network have the greatest number of host. then assign it as
the first subnet.
ex: ISP wan = 20 Host
IP AD=192.168.1.0
Second you must have a knowledge about octet table...
octet table
1 2 3 4 5 6 7 8 1stoctet
9 10 11 12 13 14 15 16 2ndoctet
17 18 19 20 21 22 23 24 3rdoctet
25 26 27 28 29 30 31 32 4thoctet
128 64 32 16 8 4 2 1 delta
128 192 224 240 248 252 254 255 SUBNET
- MASK
USING octet table u can determine the usable ip adresses.
isp wan have a 20 host so its means
20host delta=32 subnet mask=255.255.255.224
ADD THE DELTA=32 IN THE IP ADRESS :
192.168.1.0
+ 64
------------
192.168.1.64
configuration:
192.168.1.0/27
192.168.1.0/27-NEtwork address
192.168.1.1/27-1ST USABLE IP ADDRESS
.2/27-2ND USABLE ADDRESS
.62/27-LAST USABLE IP ADRESS
BEFORE THE 192.168.1.64, 192.168.1.63 IS THE BROADACST ADRESS.
SO,
192.168.1.63/27-BROADCAST ADRESS
THEN
192.168.1.64.0 IS A NEW IP ADRESS, BUT WE DON'T NEED THIS!!!
SO FROM 192.168.1.1 TO 192.168.1.62, YOU CAN GET ANY IP
ADRESSES FROM THAT,
OK
| Is This Answer Correct ? | 29 Yes | 16 No |
Answer / anand gupta
VLSM is stand for Variable Length Subnet mask,it is used
for break one network to some small networks according to
requirement of user.it is used classful address.
| Is This Answer Correct ? | 10 Yes | 3 No |
Answer / kanth
VLSM:Variable length subnet mask
general ip addressing is class full subnet mask where as
coming to the VLSM it has class less subnet mask.
Classful routing protocols require that a single network use
the same subnet mask. Therefore, network 192.168.187.0 must
use just one subnet mask such as 255.255.255.0.
VLSM is simply a feature that allows a single autonomous
system to have networks with different subnet masks. If a
routing protocol allows VLSM, use a 30-bit subnet mask on
network connections, 255.255.255.252, a 24-bit mask for user
networks, 255.255.255.0, or even a 22-bit mask,
255.255.252.0, for networks with up to 1000 users.
| Is This Answer Correct ? | 9 Yes | 4 No |
Answer / praveen singh
vlsm- it stand for variable length subnet mass.in
vlsmsubneting can be done on the basic of host id for
portion bit .
| Is This Answer Correct ? | 29 Yes | 25 No |
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CCNA 
