Building a slide deck, pitch, or presentation? Here are the big takeaways:

  • Google Cast-enabled devices are flooding Wi-Fi networks with enough MDNS packets when they come out of sleep mode to crash routers.
  • The problem needs to be addressed by Google, but until that happens several Wi-Fi router manufacturers have released firmware updates to fix it.

Packets being sent to Google Cast devices have the potential to flood Wi-Fi networks to the point of overwhelming them, hardware manufacturer TP-Link said in a blog post.

The problem isn’t unique to TP-Link devices either: Linksys, Netgear, Synology, and ASUS router users are also affected. But don’t worry: It’s not your router that’s the problem. It’s Google.

Google Cast, used by Android devices, Chromecasts, Google Home, and other devices, is designed to stream media from one device to another. In order to do that, Cast-enabled devices need to send packets to each other to keep the connection open.

That’s all well and good until you put a device to sleep.

More like nightmare mode

Google Cast-enabled devices and apps ping devices they can cast to, which they typically do every 20 seconds to ensure that the connection is still live.

Put the Cast-enabled device or app to sleep, however, and it doesn’t stop trying to ping. It keeps all those packets ands saves them up until it wakes, at which point it floods the network with every single attempted ping in a matter of a few seconds.

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According to TP-Link, the total can exceed 100,000 packets, and the longer the Cast-enabled device/app is asleep the bigger the flood will be. It’s often enough to take down primary router features, including wireless connections and access to the internet.

The Register points out that the cause comes from the type of packets being used: multicast domain name service (MDNS), which uses the user datagram protocol (UDP). UDP doesn’t have any form of congestion control, so when 100,000 or more packets hit your Wi-Fi network the only way it can react is by completely freezing up.

Fixes are available

It’s not your router’s fault that this is happening, so until Google releases a patch for Cast-enabled devices the problem won’t truly be solved.

In the meantime, Linksys, Netgear, and TP-Link router owners can try updating their firmware. Those with Asus or Synology routers will have to wait for the release of an update.

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