You're not unhirable, but if you applied for a senior web systems/operations position on my team, you probably wouldn't be hired. It's not because you're not a smart guy, but you don't have the experience we're looking for. Seems pretty easy to understand.
Also, if your resume says you're a web systems person or something like that, and you can't actually explain some details about DNS is doing, I have to wonder about the mismatch...
