Solved

# subnetting

Posted on 2014-10-03

I'm studying for the Network + test, and for subnetting, I don't have a problem subnetting class C networks, but I'm confused on class B.

the method the book I'm using is to ask 5 questions

how many subnets - the formula is 2 to the X power - x = number of masked bits - no problems there

how many hosts per subnet - formula is 2 to the Y power minus 2 y = number of host per subnet

what art the valid subnets formula is 265 - subnet mask = block size aka increment number - now this is what throws me,

so, for example, if i have a class B network and the mask is 255.255.240.0 (/20) i would use the formula

256-240 = 16 so the block size or increment number is 16. in the book, he makes a chart like this

subnet 0.0 16.0 32.0 48.0

first host 0.1 16.1 32.1 48.1

last host 15.254 31.254 47.254 63.254

broadcast 15.255 31.255 47.255 63.255

so does this mean that in the first column for instance. if the address is 172.16.X.Y the first host address is 172.16.0.1 and the last address in subnet 0.0 is 172.16.15.254? which means there are LOTS of hosts?