You should not need a gateway, mine doesn't have it. I'm assuming you are connecting the pi to hdmi or any monitor and keyboard by usb?
I would troubleshoot the ethernet port on the pi by connecting the pi to your computer with the network cable, and trying to ping the pi or ping your pc from the pi, either way works.
Also, take note on the IP you get assigned on the pi by running this on the pi console:
> ifconfig