C-8 Disconnecting from LAN, but Zigbee Radio and Devices Keep Working

Hello,
I recently started experiencing problems with hub, getting disconnected from LAN and unable to access it in any way (including 8081). The problem started happening after I gave it a static IP setting. The first night it disconnected, I didn't think much of it, so I just restarted it from power and continued using it as before. The problem happened again a few hours later/the other day, and I decided to investigate a bit more, but didn't find anything useful. On the 3rd time it happened, I did a soft reset, but some time later it disconnected again. I did a network reset, using the button on the bottom of the hub, the problem seemed gone for a few days, but it happened twice during the last few hours. I'm not sure what else can I do, and what logs can I see?

Model of Hub - C-8
Platform/firmware on hub - 2.3.6.146
How is it connected to the LAN? - Ethernet
Hub networking - DHCP
DHCP Reservation set on Router/Server? - Yes
How is Hub being powered? - Supplied power block - Connected to a UPS, along with the router itself.

The symptoms you describe suggest there are other LAN devices using jumbo frames on the same network segment as the hub. Either reconfigure these devices to not use jumbo frames, or move your hub to a network segment where all the devices only use standard ethernet frames.

Also, check that the IP address did not change (happened to me yesterday on my C-8 after being on the same address since I got it a year ago).

Do you know how can I potentially check for this? I'm using a Mikrotik CRS326-24G, and I can see the MTU on my physical ports and this is the result:
image
It seems that it's above the standard 1500, but is that considered jumbo frame? I thought that jumbo frames are considered those above 9000, maybe I'm wrong.
However, I'm not sure how to check the MTU to wifi devices.

I've assigned static ip address on the router side, so not possible.

Did you make a DHCP reservation AND a static assignment on the device? I know the Cisco switches have a feature that can block devices if they aren't assigned by the internal DHCP server.

I'm curious how you can tell it is unreachable. I saw some other posts saying that the mdns stopped working, so hubitat.local no longer works, but using the IP directly still works.

When the device is offline, is the ethernet link light still lit?

When the device is offline, do the counters on your router/switch for the HE's port still increment?

What's the DHCP lease time configured for? Does it stay online for only that amount of time?

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Sorry for the long delay before I respond, I wanted to know more about the problem. First things first, the problem can be solved by simply unplugging and plugging the Ethernet cable, or simply disabling/enabling the switch port remotely. When the problem is happening, the switch tells me that DHCP server is offering IP address, but hub isn't taking it.

The problem started happening few times every day, so it's becoming really frustrating. I can probably find a way to execute a script on the switch that will restart the port every X minutes, but that's a workaround and not a real solution.

@ian.boje To answer your questions - Originally there was only DCHP Reservation, then I made static assignment on the hub, then I reset the hub's networking and now it's again only DHCP reservation.

I'm curious how you can tell it is unreachable. I saw some other posts saying that the mdns stopped working, so hubitat.local no longer works, but using the IP directly still works.

I'm only ever reaching the hub by IP or findmyhub portal, never through the DNS.

When the device is offline, is the ethernet link light still lit?

The device is never offline, just LAN connectivity is dropped, but zigbee/zwave continues working.

What's the DHCP lease time configured for? Does it stay online for only that amount of time?

It's 30 minutes, I'm not sure if it disconnects only when renewing the lease or at random intervals.

Not sure if it is typical to have it so short? Most consumer equipment would default to 24hrs. Not saying there should be anything wrong with that, but may be causing some sort of issue.

You could maybe try setting it higher to see if anything changes. Or possibly remove the DHCP for the hub and set the static IP directly on the hub, eliminating the DHCP as a possible issue.

Also, what is your subnet mask? There have been problems in the past when using something other than 255.255.255.0 (/24) on DHCP. I think there is a special endpoint to force the correct mask on the hub, would have to search around to find the post about it.

It is not. The default on most, if not all that I know of, DHCP servers is 24 hours. The average user should have no need to change this. For home use one can extend to 48 hours without issue.

DHCP lease time should not be a factor if there is a reservation set. The reservation lease time is essentially indefinite.

Not sure if it is typical to have it so short? Most consumer equipment would default to 24hrs. Not saying there should be anything wrong with that, but may be causing some sort of issue.

The router came with 10 minutes default, I think, but I've just increased it to 6 hours.

The subnet mask is /24 for the network.

That seems very low for the default.

I just looked at the online manual for the Mikrotik CRS326-24G and the default is actually 0s, which means the lease never expires:

https://help.mikrotik.com/docs/display/ROS/DHCP#DHCP-Leases

"lease-time (time; Default: 0s) Time that the client may use the address. If set to 0s lease will never expire."

You might want to change the setting back to the default or at minimum 24 hours (86400s).

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Can you PM me the hub id? I'd like to try adding it to the beta program and see if upcoming 2.3.7 hub software handles reconnects in the short DHCP lease scenario.

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@jkudave I've changed the lease to 24h and reset the hub's networking, to see if it helps.

@gopher.ny Sure, I will DM you to figure out next steps

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Even with the beta firmware and 24h lease time, still no progress and random disconnects happen every 30m to 7-8-9h.

@gopher.ny I think my C-8 is completely dead when it comes to LAN... Everything zigbee still works, but resetting the router/switch, resetting the hubitat, unplugging the ethernet port, all of those do nothing. I got 2-3 seconds of connectivity after I reset the port/hub, but then it completely dies:

Good thing most of my stuff is zigbee, but the situation kinda sucks. Even if I wanted to do something extra, like soft reset, there is no way I can do it in the limited time I have while it's still connected to the lan.

I've brought back my old TP-Link and connected it to the main router as AP. The hubitat is now connected to it via Ethernet and seems to work and be stable since my last post. Will see what the state will be in the morning.

Out of all the things you did try, did you totally power off the hub for 10+ seconds in there anywhere? Did not see that mentioned.

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Yes, that was one of the many things. It's been stable for the last few hours after changing the router.

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Do you have your Ethernet speed set as auto or fixed 100?

It's fixed