A cyclohexene ring carries an ethenyl (vinyl) group on the sp3 carbon next to the ring double bond. Under the 2013 IUPAC recommendations a ring is senior to a chain, so the ring is the parent. What is the name?

The ring (cyclohexene) is the parent and the ethenyl group is the prefix. The double bond occupies C1 and C2. The substituent is on the carbon adjacent to the double bond, which can be numbered 3 (going one way) or 6 (the other way), and the lower locant 3 is taken. Cyclohex-2-en-1-ylethene uses the chain as parent, contrary to the stated rule. The name is 3-ethenylcyclohexene.