It's completely off-topic (this is about copyright law) but here's an answer anyway: Patents are ideally about new inventions, which means that if someone can f

It's completely off-topic (this is about copyright law) but here's an answer anyway: Patents are ideally about new inventions, which means that if someone can find 'prior art' (evidence someone was doing it before you) they can get your patent thrown out. (Ideally, extant prior art prevents the patent from being issued in the first place.) An RFC, pretty much by definition, is very good evidence of prior art, especially if it's a very well-known one, as all of the ones relating to TCP/IP are. In the real world, things get not so much more complex as a whole lot stupider. Still, I think the courts could muddle through that one with minimal problems.