Why is Devices IP address Changing Every 3 minutes?

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Why is Devices IP address Changing Every 3 minutes?

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4
NAS
DS220J, DS420J
Operating system
  1. Windows
Mobile operating system
  1. Android
Synology 2600 Router, Latest SRM 1.3.1 Update 2
A wireless Honeywell Thermostat, a 2.5G wireless device on my home LAN, is used as a DHCP client.
The IP address for that device will change approximately every 3 minutes. This has been confirmed on three different thermostats.
When viewing the router's Traffic Control page, the Thermostat's IP address can be seen to increment by one approximately every 3 minutes.
The thermostat operates through these IP address changes until, eventually, the thermostat goes OFFLINE, and the thermostat has to be rebooted to be reassigned by the router.
If I assign a DHCP reservation for the Thermostat, the router will, in a few minutes, assign a different IP address to the device.
Threat Prevention is OFF for these devices.

Is there a router setting that is perhaps not allowing the router to interface correctly with the thermostat? Rolling the IP is fine, but for whatever reason, within the day, the thermostat will go offline.
 
Rolling the IP is fine, but for whatever reason, within the day, the thermostat will go offline.
Can't help with your main issue, but the reason it goes offline after ~1 day is probably because it cycles through the router's entire DHCP IP range before these run out and it goes offline.

It does sound like the thermostat is faulty / has a bug...

Does the MAC address of the thermo stay the same with each IP assignment? If these are being regenerated randomly due to a bug, each new MAC address would be assigned a new IP by the router, which could explain what you're seeing.
 
Can't help with your main issue, but the reason it goes offline after ~1 day is probably because it cycles through the router's entire DHCP IP range before these run out and it goes offline.

It does sound like the thermostat is faulty / has a bug...

Does the MAC address of the thermo stay the same with each IP assignment? If these are being regenerated randomly due to a bug, each new MAC address would be assigned a new IP by the router, which could explain what you're seeing.
Probably. It happens with three different Honeywell Thermostats made up of two different models so points to a bug.
 
I was going to ask the same thing about the MAC address being changed. I’ve never seen anything like this on any DHCP server or client device. Is it possible to configure the thermostat directly?

There is the DHCP Address Lease Time which dictates how long a client assignments lasts. Is this set to 180 seconds? Mine is 86400 seconds, or 1 day.

The puzzling thing is that with the IP reservation the address should always be the same, for that MAC address.
 
The puzzling thing is that with the IP reservation the address should always be the same, for that MAC address.
Could be that it's randomising the MAC address as a security measure...and this mechanism is what's buggy. MAC randomisation is becoming more common in OS's - eg Linux, iOS for certain connections - though not encountered it in an iot device before...
 
I was going to ask the same thing about the MAC address being changed. I’ve never seen anything like this on any DHCP server or client device. Is it possible to configure the thermostat directly?

There is the DHCP Address Lease Time which dictates how long a client assignments lasts. Is this set to 180 seconds? Mine is 86400 seconds, or 1 day.

The puzzling thing is that with the IP reservation the address should always be the same, for that MAC address.
yes good thought. The MAC address matches the label on the unit and does not change, as read by the router through this behavior. While the IP address is changing, I still have, via the app, functional use of the thermostat. The DHCP lease time starts at 24 hours. Honeywell doinks or Resideo support now I guess, said it should do that, then another support person said it should not. I would guess there are networking rules that say its a bad idea.
 
Last edited:
If you have another/old Wi-Fi router you might test how the thermostat works with another DHCP service.

~~~~~~~~~~
Additional

I recently replaced a Honeywell CM5000 thermostat. Basically a 2xAA battery powered, 7 day, digital timer switch. I guess in the ‘90s it was cutting edge.

I considered getting something smarter but ended with the 2020’s equivalent, a Honeywell T4. A few more features and easier to use. After the 5 minutes fitting and another 10 to setup, we haven’t had to spend more time to debug it. I hate DIY so this was great, it even covered the same wall space so no decorating too! Also, received praise… for once.

The only minor point is the temperature sensor is now accurate, so it feels cooler in the house. One reason we replaced the old thermostat, those extra hidden 6C are being missed.
 

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