To do this you need to enable "AP Isolation" in the advanced settings.
The Wiki has the details.
From the linked article:
AP Isolation
The default value is Disabled.
The help file says...
This setting isolates wireless clients so access to and from other wireless clients are stopped.
How it works:
Wireless access points work by bridging the wireless port to the wired switch ports and router port. Everything happens at the MAC address level and does not involve IP addresses,NETBIOS over TCP/IP (also known as MS Networking). Just MAC addresses.
The wireless bridge builds a bridging table consisting of a table of "heard" (or sniffed) MAC addresses that appear on various ports. Think of the router having just 3 available ports; Wireless, Ethernet switch, and router port. If the destination MAC address of a port is shows up in the MAC address table as sitting on a specific port, only that port gets the traffic. Broadcasts, which have no destination MAC address are sent to all ports.
When this feature is enabled the software builds a logical rule (or filter) for these MAC addresses and ports that says:
"If the packet originates on the wireless port, it can only send and receive packets that are destined or originate from the router port or ethernet switch port."
Not a very complex rule, but one which totally prevents wireless client to client traffic. Not even broadcasts will go from wireless client to client.
-prevents one wireless client communicating with another wireless client.
-This breaks the connection between WLAN and WLAN
-No improvement in performance, performance is exactly the same. The difference is in "reliability" or ability to survive in a multi-path environment.
-You enable this if you are running a hotspot. Click Network Neighborhood in a motel sometime, see if the motel needs to set AP isolation.
-Changing this from the default value would be for security reasons.
I think this is the "AP Isolation" setting. I have not heard anything about it improving performance though. – Darth Android – 2014-01-30T17:00:09.083