Link: https://old.reddit.com/r/homeassistant/comments/1vp63i4/badly_managed_subnets/

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The original was posted on /r/homeassistant by /u/3d-designs on 2026-08-15 15:43:38+00:00.

I've been skirting on running out of addresses on my /24 subnet for some time and as I'm adding more esphome devices, it was clear that I'd need to increase it.

So, I modified the subnet mask on the LAN from the /24 to /21, to give more a lot more space and avoid clashing with some separate VLANs I already have in place. Simple enough to do and, apart from some reboots, relatively painless - or so I thought!

After an annoying amount of unnecessary problems, I have discovered that a worrying number of manufacturers have simply ignored subnet masks and assumed everyone is using /24, it would appear.

Top of the naughty list appears to be Amazon. Many of my echo devices failed if they picked up an address outside a /24 range, as did a FireTV stick.

My Roborock vacuum suffered the same problem. I suspect that my Mammotion mower is seeing the same effect.

Now, it's easy enough to fix with some DHCP reservations, but it really shouldn't be necessary. Moreover, I would have thought it would be more work to deviate from a standard IP stack, than to standardise, but it seems not.

I mention this for two reasons.

1. I just wanted to moan as it's pissed me off by creating unnecessary work.
2. I can't imagine that I'll be alone in seeing this, so it may be useful for others to know.

Two further points for clarity:

1. Of course, HA worked fine and was quite happy for me to change its subnet mask and it carried on perfectly.
2. This problem is definitely real, as I subsequently found numerous discussions about the limitation in Amazon devices.

Why do something badly when doing it properly must surely be easier?