This article has help me get out of the dark on this. But I'm still fuzzy on something. In looking over some test questions for an exam I saw a question with an IP of 192.168.0.100 that asks you to guess what subnet mask address it uses 255.255.255.0 or 255.255.240.0 with no other info given. The answer was 255.255.255.0 but I don't understand how they got this. I know the default subnet mask of a class C address is 255.255.255.0 but how do you know when you should use this or 240 etc etc

Thanks
qb