Hi tcacfoh,
If you purchase the D-Link 815, you’ll find there are 5 ports on the back. 1 Labelled ‘Internet’ and 4 labelled ‘1, 2, 3, 4’.
You will need to plug your MixRack into any of the 1, 2, 3 or 4 ports. The one single separate port called ‘Internet’ is only for upstream or internet traffic.
Hope this helps,
AndyH