Thanks for your reply. I would presume that if it was something on the internal LAN, then the information would be received (Rx) then transmitted (Tx) to another port? It is only being received Rx, not Tx.
The red bars are ethernet 0 which is the internet WAN, all other ports go to internal LAN devices.
As to the Dos or portscan, I know what these are, but have no idea how to test for either, and I have no idea what a tcpdump is, or how to carry it out, or even how to interpret any result I might get.