Block incoming traffic to specific computer

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http://serverfault.com – I have a router that is connected to the internet. To that router we connect via LAN and WAN. WAN settings are up, router user/pass, router access is secured with WPA/WPA-2. I want to make some computers, to be connected to the router (lan or wan) and will be protected from the outside world. What is the best way doing so ? the computers firewall must be turned off. the router firewall is on, it is a cheap typical TP Link router - TL-WR741N / TL-WR741ND. Are these setting enough ? to set the firewall On on router, or maybe i can block incoming traffic to certain ips - the ips of computers (HowTos)