Isolate LAN port from the rest of LAN while giving it internet access

[amita]

Hi,

I would like to isolate some computers in my network from the rest of the devices in my home network, while enabling them to use the internet connection. all the computers that I would like to isolate are connected behind a switch / wireless AP that is connected to the Assus on LAN port #4.

My question: Is there a way to define for a specific LAN port of the RT-N66U to be isolated from the rest of the LAN network and only allow it to access the internet?

Thanks,
Amit.

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More info: the current configuration:
Level 1:ADSL MODEM (Bridge) ->
--Level 2:Asus RT-N66u (main router, with DHCP server on it, running Merlin FW 3.0.0.4.374.34_2) ->
----Level 3:Asus LAN1..3 connected to home computers and LAN ports of wireless APs/switches,
----Level 3:Asus LAN4 connected to LAN port of wireless AP/switch from it guests are connected. the guests on this port should be separated from the rest of the network.

The reason to connect the guests using standalone wireless switch and not connect them the the Asus guest wireless network is since it is located geographically far from the Asus main router.

I prefer to use this direction of solution (LAN PORT based isolation), if possible, in order to keep usage statistics tracking about the guests computers.