Hi,
Unfortunately it has been a while since I did this and I can't exactly remember what I did. I think I got lucky!
But the first thing I had to do was set up one of the ports as a Virtual LAN Port (I think!). See LAN Ports and then enable one of them for an ethernet port.
I will send my config file to Keith so he can post on his site. I hope this willl help.
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TPLink router