question about subnetting with VLSM

[jpcapobianco]

hi,

i have a question about subnetting using VLSM

i start from

192.168.15.0  /24

then use the  /26  prefix with this address and i have:

192.168.15.0       /26

192.168.15.64     /26

192.168.15.128   /26

192.168.15.192   /26

now i re-subnet one of these subnets:

192.168.15.128   /26 and i use /30

how many subnet can i obtain ?

i think 16 because i'm borrowing other 4 bits from 26 to 30.

but i'm not sure if i have to consider the initial /24 , in that case the subnet will be 64.

can someone explain to me ?

do i have to considere 2^4 borrowed from /26

or 2^6 borrewed from /24  ???

thanks

[Marvin Rhoads]

16.

Each /30 uses four numbers - the network number, the broadcast address and two host addresses.

You are working with the range from 128-191 = 64 numbers. 64 numbers / 4 numbers per /30 network = 16 each /30 networks