I am looking at a question which stumped me.

Which of the following IP host would be valid for PC users,
assuming that a /27 network mask was used for all of the network?

a - 15.234.118.63
b - 83.121.178.93
c - 134.178.18.56
d - 192.168.19.37
e - 201.45.116.159
f - 217.63.12.192

I think the answer is only "d" because /27 is class C and
also blocksize of 32 which "d" would fall under. Is this correct?

Regards
Shawn'

The Oracle Says:

The question can be answered in a few seconds using the Subnetting Secrets Cheat Sheet. A /27 mask tells you to tick across the top three places giving you subnet increments of 32. Write out the subnets starting with 0 and keep going up. Any of the above numbers which are either a subnet or broadcast number are not allowed, the rest are so:

0
32
64
96
128
160
192

a - 15.234.118.63 <- host 63 is a broadcast number for the 32 subnet
b - 83.121.178.93 <- host 93 is OK
c - 134.178.18.56 <- host 56 is OK
d - 192.168.19.37 <- host 37 is OK
e - 201.45.116.159 <- host 159 is a broadcast on the 128 subnet
f - 217.63.12.192 <- host 192 is a subnet number

So the answer is b,c and d are all OK to use. The others are either subnet or broadcast numbers. I hope this makes sense. If not please read the Subnetting Secrets members only section.

The Oracle