Valid host address

in CCNA & CCENT
Can anyone explain a method for fast calculations of valid host addresses within a subnet ?
255.255.224.0 gives us 16 nets with 4094 host per net.
Lets use 172.128.208.0 as the subnet id.
What is the Host Address Range?
Well, I know the first valid host on this subnet is
172.128.208.1
The way I currently calculate this would just to keep adding 255 until I hit 4094. ugh
any shortcuts ?
255.255.224.0 gives us 16 nets with 4094 host per net.
Lets use 172.128.208.0 as the subnet id.
What is the Host Address Range?
Well, I know the first valid host on this subnet is
172.128.208.1
The way I currently calculate this would just to keep adding 255 until I hit 4094. ugh

any shortcuts ?
Comments
Working on
Learning Python and OSCP
255.255.224.0 will give you 3 subnet bits and 13 host bits which is 8 subnets and 8190 hosts per subnet. To find the ranges you need to write out all the combinations of subnet bits, then put all "0" or all "1"'s to find the lower and upper bounds respectively.
16 subnets
256/16 is 16 so your increment is 16
Add 16 to the subnet octet and -2 to get your last host
172.128.208.1 - 172.128.223.254
That is how i do it in my head but i am pretty quick at mental arithmetic
Working on
Learning Python and OSCP
Glad it helps
It got me through my CCNA
Working on
Learning Python and OSCP
can you give an example of this ? and off topic , can you use a calculator on the exams ?
nope no calculators allowed...... all you get is a wipe board n marker pen....