Fing Warning on Eero Max 7: Network netmask (prefix length) is not tuned correctly / Local DNS Caching

[bradmaestas]

I recently had Sonic 10G fiber installed and am using an eero Max 7 router. Upon the first scan in Fing, it threw an error about the subnet mask being oversized.

Home network is too wide: 192.168.4.0/22, up to 1024 devices

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.

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. 255.255.255.0 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.

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.

The standard eero app certainly does not let you get into that depth of control and as far as I can tell, the router does not respond to access attempts on its IP address directly (ie. no web portal). Is this something that I should even care about? Thoughts?

My second question relates to eero's Local DNS Caching option. From what I have read on these forums, it is not terribly useful and tends to create issues for those using manual DNS settings. I am not currently using any manual settings on the router, other than some port forwarding. Does anyone have opinions on this feature as well?

As for my use case, I am a musician that occasionally does low-latency remote lessons and performances over Zoom. I am an audio engineer, videographer, and still photographer that deals with large files on a daily basis. I am running a Roon Nucleus music server on my network. I do not currently have a NAS but am considering it in the future. Thanks!

[js9erfan]

How many network devices do you plan on using? A /22 is rather large for home use. I don't use eero's but you should be able to change to a /24 or smaller using the eero app. I typically prefer vlans over a flat network to keep devices isolated as needed (especially iot devices) while cutting down on the noise. If you're not seeing issues with your /22 then you can probably leave it alone.

I can't speak to eero's dns capabilities/performance but If you want more control over dns see this post. If I wasn't using pfsense/unbound w/ pfBlocker I'd probably be using a pi-hole on my home network but then again that's just me.