Good advice above - for your router table, the under the table collection effectiveness is going to be fairly weak with a vac unless you have a really close fitting box around your router (which may lead to overheating). If you have even a medium size box, a vac is not going to be effective IMO. mleny77's configuration is going to be better. Vacs are good at collecting dust close to the pipe (which is the case above the table), but don't have the necessary flow to capture dust in a large or even medium size area. For example, the Festool vac is about 140CFM, whereas even a cheap single stage dust collector is going to be pulling 4 or 5 times that amount.
Of course some collection is better than none, but just setting expectations