RFC1918 is fine, it's easy enough to remember a few networks. But what if you are asked for RFC3330? Say, the question asks you to block the networks in RFC3330 on the Internet facing router. I cannot find a place on the Cisco document website for this RFC, and I don't think I can remember all these networks.
Another sample is to block ICMP Smurf and UDP Fraggle attachs. Without searching, I cannot come up with an idea what they are.
So how likely this kind of questions are asked? And if asked, what are you gonna do?