Using a dovetail jig on a router table is not the easiest way to cut a dovetail joint as getting a good registration of the 2 pieces of wood that will make the joint is quite difficult.
A dovetail jig that that allows both pieces wood to be accurately aligned as the dovetail is cut is a much better way of doing it. There are a lot of jigs available but they can be quite pricey. The Trend and Incra jig are good examples.
If you want to use one on a router table then the Leigh jig has a good reputation but I have not used one.
