Why "192.168.1.0 /24, subnetting it to multiple /30" is not an example of Subnetting

[raizemaru]

Hi Everyone,

I'm a little confused about option B, why it's not part of VLSM example ??.

I think 192.168.1.0 /24 could be subnetted to /29.

Question: Which of the following options are examples of VLSM?
A. Taking the 192.168.1.0/27 and subnetting it to multiple /30s
B. Taking 192.168.1.0/24 and subnetting it to multiple /29s
C. Taking 172.16.1.0/24 and subnetting it to multiple /26s
D. Taking 10.1.24.128/26 and subnetting it to multiple /28s
E. Taking 172.16.0.0/16 and subnetting it to multiple /24

[acampbell · Accepted solution]

Hi,

Because in OPTIONS B & E you are using just what is referred to as
"subnetting" with each subnet having the same mask length.

VLSM is art od taking a subnet andsubnetting that.
IE// the subnets have variaile lengths.

See thevlink enclosed from Cisco TAC engineers.

http://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/13788-3.html

Hope this helps
Regards
Alex

[raizemaru]

Hi Alex,

Ok, now I'm uderstood why the Opt B is not include in the VLSM example. Thanks for your explanation..

Regards

[brhoom6080]

Because VLSM means subnetting a subnet. B and E are not considered subnets because they have not been subnetted yet. 

B. Taking 192.168.1.0/24 and subnetting it to multiple /29s  

192.168.1.0/24: If you look at the table it's a class c default which means it's not subnetted yet.

E. Taking 172.16.0.0/16 and subnetting it to multiple /24

172.16.0.0/16: If you look at the table it's a class B default which means it's not subnetted yet.

Everything else has been subnetted for example

A. Taking the 192.168.1.0/27 and subnetting it to multiple /30s

192.168.1.0/27: If you look at the table it's a class C and it's not default which means it has been subnetted.