Probably not the answer you’re looking for, but it’s the correct one.
All of them. The OSI model is just that– a model representing Network communication. The OSI Layer’s are defined to detail specific functions that are preformed in network communications in a manner that is easier to comprehend.
Some protocols, by their nature, lend themselves to predominantly work in one layer over others but they all pass through all 7 conceptual layers.
Take a look at these OSI examples:
http://www.tcpipguide.com/free/t_UnderstandingTheOSIReferenceModelAnAnalogy.htm <- this one uses a good analogy of transferring a letter between CEO’s
DHCP goes all the way to layer 7.