FortiAP, ARPs and Amazon Echos

There is no secret that “smart” speakers are a great addition to add to your home. They can be used to inquire about the weather, serve as an in home intercom and even a multi-room sound system. In order for some of these features to work, the speakers must be able to communicate with each other locally via a wireless network.

While attaching these devices to my network, I encountered an issue while trying to create a “speaker group” within my Alexa app. It was the weirdest problem, when I selected the echo in my kitchen, my echo in my bedroom showed offline. However if I selected my echo in my office, the one in the bedroom showed online while the one in the kitchen showed offline. Needless to say, when encountering this initially, I found this bizarre and thought something was really wrong with these devices.

However, after taking a step back, I was able to solve after modifying the default setting associated with an SSID. In this blog post, I am going to explain the default setting I had to change in order to get these devices to be able to connect to each other properly.

When creating an SSID via the FortiOS GUI (as of 6.0.3), the following settings are created by default under “WiFi Settings”:

At first glance, the only setting I thought that would block my echo to echo communication was the “Block Intra-SSID Traffic” setting. I confirmed that the setting was turned off, yet, I still observed the same odd behavior when trying to create the speaker group. After taking a second look, I saw the following:

Then I had my “aha” moment. I realized that when the FortiGate Wireless Controller was aware of a host on the local wireless network, all subsequent ARPs from to that host would be blocked. This is an ideal situation when you have the “Block Intra-SSID Traffic” feature enabled on the SSID because in that situation, the wireless endpoints should only communicate to the FortiGate. However, in the situation that the wireless endpoints need to communicate among themselves (such as my Echos), it is very necessary to allow those ARPs to be passed freely via the wireless network. Once I removed “ARPs for known clients” from the “Broadcast Suppression” under the SSID, my echos found each other without delay and my whole house speaker system started working like a champ.

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