Comment Re:Today's computer science corriculum is practica (Score 1) 154
Thank you, exactly this.
I don't know what the OP actually did, but presumably this was not an interview question (since OP said they hired them), and part of actual assigned work. I would expect any even mildly-decent developer to be able to learn about IPs, netmasks and figure out how to do calculations with them in a couple of hours, even with no prior knowledge (I say this knowing much about it myself). One of the most important skills of a developer is to be able to learn. This is not just learning new languages, libraries, techniques and patterns, but also the new (to you) business domains, user needs, and "why" behind requirements/features/stories.
On the other hand, expecting any random dev to know this off the top of their head would be asinine. If they were fired for this, then the OP did them a favour because it's probably an awful place to work. And if all three were hired with the explicit expectation of being an expert in networking but don't know what a netmask is, well holy crap, the OP needed to learn how to better screen candidates at least two hires ago.