Can a modem either DSL Cable style also be a router and why?
a modem takes cable input and output goes to only 1 Ethernet
cable. A router takes the 1 Ethernet cable and makes it so that you
can hook up four or five Ethernet cables. a wireless router allows
you to hook up 4 or 5 Ethernet cables and unlimited amounts of
wireless receivers. If you only have 1 computer, you don't need a
router. You only need 1 Ethernet cable.
To put it in simple terms :
Yes, many newer external modems have full router and firewall
functionality built-in to a single device