Fing reports Network netmask (prefix length) is not tuned correctly

My fingbox keeps reporting the following:

Network netmask (prefix length) is not tuned correctly

Home network is too wide:, up to 1024 devices

Is there a way to fix this on my Eero Pro?  I don't see a way for Fing to ignore the alerts.


More info:

Code 406: Network netmask (prefix length) is correctly configured

Failure case: Network netmask (prefix length) is not tuned correctly

Network check: information are gathered from your current network


Technical definition

The check verifies that your network subnet mask (or network prefix length) is not oversized. Although networking standards recommend to always prefer multicast and broadcast when searching for networking services and devices, many modern IoT devices have still been using unicast sweeps to find peers: this means that lookup, onboarding, pairing or service usage when you have a big network will make the device lookup for the service on a very big number of possible devices, instead of just 256/512. A good example of this is also Windows workgroup: NetBIOS is unicast, so lookup of other PC and printers in a big network takes much longer. The same happens as well to network monitoring software like Fing, Fingbox, and so on: these apps leverage ARP-sweep or ping or similar, so the time taken by a network discovery is proportional to the network size.

What it means for me

A subnet mask is a number that defines the range of (IP) addresses available within a network. It uses the same format as IP address, but in negative format, e.g. is a typical Class C mask including a range of 256 addresses. An alternate form to express it is as network prefix length, meaning how many bits of the network address are stable: a class C network is /24, meaning that 24 bits, first 3 bytes of the address, are not varying.

How I can fix this

An oversized network is much slower than a correctly sized one. E.g. a home network with dozen devices not being a Class C is definitely not tuned correctly. In order to fix it you don't have to change your local PC configuration but rather login into the router configuration and edit it. To make sure every device gets the new updated configuration you should also power cycle or reconnect all connected devices.

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  • Same issue here. No idea why. restarted network, troubleshooted ISP... Changed DNS... nothing.

  • OK, but where can I access this field to edit it? I don't see anyplace in the Eero app that gives access to this. Trying to log in directly to the eero is denied...

  • Has this been addressed? I’m getting the same error.

  • *bump*

  • I appreciate what you did.    

      • Luella
      • Luella
      • 8 days ago
      • Reported - view


      Thanks again >> MCDVOICE

  • Hello everyone,

    Based off what the OP posted it looks like you just need to change the subnet mask to change it to a class C. I didn't see a list of any troubleshooting steps taken so far so I will suggest changing to manual IP which is in Settings -> Network Settings -> DHCP & NAT. Select Manual IP and you will be able change the subnet to which should solve this. Can anyone give this a try and let me know if the device is still reporting the message?

      • Calion
      • Calion
      • 1 mth ago
      • Reported - view

      James After changing DHCP & NAT from Automatic to Manual IP and changing the Subnet IP from to, tapping Save, and tapping Reboot, I received the following message: “We couldn’t update your settings. We ran into an issue updating your settings. Please check to make sure you entered the right values and try again."

      • Calion
      • Calion
      • 1 mth ago
      • Reported - view

      Calion Am I doing something wrong here? Should I be changing the Subnet *mask*, not the Subnet IP, to To be honest, I’ve never been quite clear on what these settings do.


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