I configure servers for a tech company. We lease these out to companies that have their IT departments give us the network information so we can set them up.

The amount times I've had to kick installs back because the network information wouldn't work is astounding. Oh... You want the server at 192.168.1.250 with a gateway of 192.168.1.1, and you say you have a subnet mask of 255.255.255.248. Yeah... sure... This wouldn't be so bad if the information wasn't generally filled out by network admins who should certainly know why this doesn't work.

And if that weren't bad enough, by the time I see the configuration these types of glaring issues have been missed by two levels of engineers that should also know better. I'm the lowest paid guy here, and it falls on me a lot to tell them that it won't work.

Layman's terms: The subnet mask identifies the subnet that the server operates in. In this particular example (that I made up on the spot), 192.168.1.250 is in a subnet with 6 potential hosts, from .249 to .254. It'd be like telling you that you can park your car in one of 6 spots at your house, but the only road you can use to leave is actually located 31 blocks away.