Stopping Local Communication in android hotspot How can I stop two devices from communicating among themselves if they are connected to my Hot Spot.(for eg I want them to not be able to ping eachother)
You want to enable Wireless Isolation mode.

On the Linksys this is called AP Isolation. 

From WirelessIsolation.com:


  Wireless Isolation, sometimes called client isolation, is a setting on
  a wireless router. When this setting is enabled it prevents a computer
  that is connected to the network by a wireless connection from
  accessing computers and resources that are connected to the network by
  a wired connection. It will also prevent one wirelessly connected
  device from connecting to another wirelessly connected device. In
  essence Isolating that device on the wireless network.
  
  This is used as a method of security so that you can provide both
  wired and wireless connection through the same network without opening
  up secured computers and resources to potentially unwanted visitors.
  This can be very helpful in businesses that have a wireless hotspot
  located in their lobby for example.
  
  Without Wireless Isolation anyone on a wireless internet connection in
  a wifi hotspot would not only have full access to the computers and
  resources in the company’s network, but also to the various wireless
  devices that were using the wifi hotspot at that time.
  
  Most wireless router makers will support wireless isolation in one
  form or another, if you already have a router and are curious to see
  if it comes with wireless isolation or not you can check your products
  manual, or log into your router and check the security tab.