from another site, it appears the Bird 1197 software updates established ethernet capabilities.  That will elminate the need for the interlink module if you have a newer unit with the last number 8 (e.g. 898) .

From the few posts I have read, it appears once you ethernet them- the main unit stays as the HOME unit, and the unit that is SHARED has the waypoint show up with a green circle around it.

its very pleasing to see the advances humminbird offers with the free updates at no extra costs.