If your DSL modem is actually a modem/router (some are and some aren't) then you should be able to just use the switch. If not, then you should use the Linksys router. Even if the modem is also a router, you could still use the Linksys, but you would need to set the modem as a bridge (turning off its routing capabilities) and thus letting the Linksys do all the routing. (This is more complicated than simply using the switch). So, you need to check what model modem you have and then check out its specs to see whether it functions as a router or is just a modem.