Device disconnects from LAN randomly

[chymba]

Hello,

I am having an issue with a three provided router in which a specific device randomly loses connection to the LAN and can only reconnect after restarting the router.

I had great trouble communicating my issue to three customer support who thought disabling IPV6 would some how fix the issue, I suspect the issue is with the firmware of the ZTE MC888 router or flaw in the hardware.

The issue is as follows, as previously stated a specific desktop disconnects from the LAN, this issue did not occur on my old router, the device can still access the internet, just not services hosted on the local network, ping still works, but curl and ssh both fail. Restarting the desktop does not fix the issue, and the issue persists across operating systems.

Restarting the router temporarily fixes the problem until it occurs randomly after about 2 to 3 days, I have tried resetting the router, insomuch as not even modifying the default SSID and password, but the problem persists, I have also tried re-seating the SIM, this also did not help.

The desktop in question is connected to the second ethernet port on the router, the first is connected to a network switch which is in turn connected to a different desktop, this second desktop does not exhibit this behaviour nor do wireless devices on my network.

This bug isolates the desktop on my network in such a way that tailscale has to switch from direct connections to relayed connections when talking to other devices on my tailnet.

Any help would be appreciated in resolving this issue.

[PeteG]

Hello there.

That's strange. Are you able to test the desktop connected to the other ethernet port, swapping it with your network switch? Or, would you be able to test your desktop connected through the network switch? If so, it would be interesting to know if the same issue occurred while connected in those ways. It's also worth considering trying a different ethernet cable, just in case. 

Pete. 

[chymba]

Hello Pete,

Thanks for your reply, I'll try each of these in turn to see if I can isolate the issue and get back to you.

[JonathanB]

Thanks @chymba, please let us know when you've had a chance to check it out. I'm also wondering if the desktop is specifically only having this issue over ethernet, you mentioned that wireless devices are fine, so may also be worth checking with the affected device over Wi-Fi as well as wired.

Thanks,
Jonathan

[chymba]

Hello Jonathan,

The issue occured again today and I tried some of the troubleshooting steps Pete underlined.

First I tried swapping the ethernet ports, this did not make any difference.

Next I tried connecting both desktops to the network switch, leaving only the network switch itself connected to the router, this configuration fixed the issue and both desktops were able to talk to each other as expected.

This lead me to believe that the issue may have been with my switch, so I tried disconnecting my switch and connecting both desktops directly to the router, but the issue still occurs if I do that.

This leads me to believe that my original assessment (that there is a fault with the router) may have been accurate.

[chymba]

Update: After some more experimenting I realised that wireless devices also couldn't ssh into my second desktop connected via ethernet, however they could ssh into each other. It appears that after the router has been on a while it segregates each ethernet port along with WLAN so that devices connected to one can't talk to the other.

The isolate wireless network devices setting was in the default off position during this testing. This again points to an issue with the router firmware which has likely gone unnoticed since many users simply connect to the internet rather than devices on their own network.

@JonathanB I hope this is enough information to begin diagnosing the issue on your end.

[JonathanB]

Hi @chymba,

Sorry for the delay in getting back to you.

I've raised the issue with our device team, and it doesn't seem to be a known issue. We'll make some enquiries in case ZTE have any awareness of this issue on their end too.

Thanks for sharing all the other troubleshooting you've done so far, we were also wondering if you've tested this with UPNP enabled?

Thanks,
Jonathan