"From 7 to 11" was lifted from a very obscure album by a band called Raven. I'm not even sure where they came from, but a friend of mine had it, and played the original for me.
Led Zeppelin isn't the only band to borrow/steal liberally. As much as I love Cheap Trick, they know how to borrow when needed. I've always heard "Cry, Baby, Cry" in the middle of "I Want You To Want Me". This one just astounded me. It's REALLY obvious...