I have a FAS2040. With respect to the e0p port:
1. What kind of cable needs to connect to it? Ethernet?
2. Do I need it if I am not using an external shelf?
3. Does it connect to a shelf or to a network switch?
Solved! See The Solution
the e0P port is for connectivity to the out-of-band management ports on the IOM disk shelves.
The ports are called ACP (Alternate Control Path).
They are automatically configured by Data ONTAP upon boot up and given a random 192.168.x.x\24 address and thus automatically configures the ports on the disk shelves for the same subnet address.
There is no configuration necessary on your part except to connect the cables properly throughout the stack.
When you purchase disk shelves you will receive black CAT6 Ethernet cable with the disk shelf along with your SAS cables. If you do not have disk shelves just leave the ports alone and ignore them.
Let me know if you have anymore questions.