Can't put eth0 down

Hello, I just purchased a BeagleBone Green
I’m trying to turn off the functionality of eth0 which keeps coming up as a working port using dhcp.
When I try to use ifconfig eth0 down I get no response and the port stays connected
When I use ifdown eth0, i get ifdown: eth0 not configured and the port stays connected
the /etc/network/interfaces file as shipped does not configure the port, the lines to set it as dhcp are commented out
something else is configuring the port.

How can I disable the port?