What could cause a router to reboot?

Having tried 6 different routers, each having an issue where they randomly restart, be it on the mains power or via a UPS, is there anything related to the phoneline that could cause this behaviour?

The BT Hub 6 actually adds an entry into its log that states:

Current boot was caused by Power Reset

After the reset, could shorting the pairs cause it to happen?

Shorting the pairs? Well should not be doing that and would confuse a system and might cause a reboot and might break something too.

I'm trying to ascertain what could cause the router to reboot as BT don't know.

I tried shorting the middle pair on the router itself but it doesn't seem to care, I have enough routers that they are expendable at this stage, I just want to get to the bottom of whats causing it.

Hi

Domestic routers can often reboot, they are cheap and built to a low price point and are never considered mission critical by the manufacturer.

Things that can make them reboot:

Power problems
Software problems like memory leaks
Kernel panics, some low lever driver in the software causes a crash
Hardware problems, i.e. poorly designed hardware that causes the router to crash

It should be noted that what might be written in the log may not be the actual cause. For example the router may have a watchdog timer, this looks to see that the code is running as the code constantly updates a timer, so if the code freezes the timer fails to update so the watchdog will issue a reset, this may look like a power off/on to code that is writing the logs.

If you have something on your network that is opening a lot of connections/ports this could swamp out any chance of the inbuilt firewall/NAT keeping track of the them, with the area of ram allocated to keep track of all these filling up to full which may be treated as an unrecoverable fault and it crashes and resets. Something like this might explain why you have had issues with other routers.

How often do they restart? When you say different routers, what models have you tried? How many devices are connected?

Regards

Phil

Edited by PhilipD (Wed 23-Jan-19 15:55:45)

BT Hub6
Fritzbox
Plusnet Hub one x2
Thompson Gateway
Openreach Modem + Router

Very underutilised connection, nothing running beyond streaming amazon or netflix, it will randomly reboot with no real pattern.

Have you tried plugging into a different mains socket? Using a long extension cable if necessary because the router has to be where you have it now.

Are you always using the power supply cable that comes with each router, or always using the same one?

Yes, it was actually in a completely different room whilst BT had changed the routing of the cable to avoid interference issues (but made no difference). The PSU is changed each time a new router is tried or purchased.

Hi

How often are the reboots? It's not that unusual for domestic routers to reboot every several weeks for seemingly no apparent reason.

It could be you have some sort of denial of service attack happening, there are several that will cause routers to reboot, are you on a static IP address? If yes, it might be worth trying to get a change of IP address, if no, are you receiving the same IP address each time you connect, again if yes, you need to see if you can force a new IP address.

When you were on an Openreach Modem + Router, was it only the router rebooting in that case? If Yes, rules out anything interference I should think coming down your telephone line as it would have affected the modem.

I think you can rule out power issues given you have tried a UPS, and the switch mode power supplies used are pretty forgiving to brownouts etc anyway, and will often work quite happily at lower voltages and care little for any mains Hz frequency variation, this is why most power bricks work internationally (from 120v 60Hz upto 240v 50Hz) without any changes to settings etc.

To confirm, when you say reboots, do you mean the line is dropping and re-syncing or do you mean that the router is crashing and rebooting from scratch?

Regards

Phil

Edited by PhilipD (Thu 24-Jan-19 10:51:28)

Router is rebooting according to the logs, the logs are either wiped, or the date resets to 1st jan until it can contact the NTP server. It's not just a line drop.

IP is dynamic, when the router+modem combo was used, I believe both would be restarted.

The resets occur at least once a day, sometimes several in a short space of time.

As there are 2 plusnet routers, they were both connected, one to the broadband and the other just to power, when the one connected to the broadband restarted, the other one did not - that in my mind would also rule out any issues with the power.

Do you have anything connected to the LAN ports of the router?

Yes, a switch, a Linksys PAP2 and powerline adapters.

I've isolated the other network devices by going into a switch first now, and then 1 cable to the router.

Hi

Worth doing a search for "powerline adapter causing router to reboot". Best to rule them out, they are the devils work

Regards

Phil

So we had the ethernet going into a technicolor gateway, then linked to the hub 6 via a cable, both devices reset.

I have often wondered whether spikes on the power supply can cause problems like the one you have.

Hi

It would need to be a drastic spike, the reason being is how the power supply for the router is derived from the mains. The power-brick, now we have lighter ones, are switched mode power supplies, these take the mains AC at 240 volts and converts it to DC with a resulting DC voltage of ~ 340 volts, with components usually rated at 400 or 500 volts in the primary side.

This DC voltage is then turned on and off at a very high frequency under the control of a chip based on feedback from the output voltage, and there is no direct connection between the mains and the resulting DC voltage. Any spikes large enough to cause a blip on the output would be damaging other equipment in the home constantly, i..e a rebooting router would be the least of your concerns and things like the TV would be rebooting, PVRs, games consoles, the computer etc.

The output voltage of 12 volts (typical for routers/modems) is then switched down to even lower voltages in the device (3.3 volt or less), making it even less likely that a voltage blip (of which there are many on the mains supply) would make it all the way to the router itself.

Also the OP has said they get the same problem with a UPS.

Regards

Phil

Hi

You really need a good troubleshooting approach now to find out what the cause is:

Example:

1) Take the router prone to rebooting, have it turned on but not connected to anything including the telephone line, does it reboot now? If Yes, it's likely some interference coming in from the mains supply or a rather odd mains supply problem, or could be RFI from the air.

2) If no reboots, you can consider the power side fine, so now connect it to the telephone line and let it sync up, but connect nothing else and do not use the connection, does it reboot now? If Yes, then likely EMI coming in from the telephone line or some voltage that shouldn't be there.

3) If no reboots, connect it up to your network switch and start connecting things back to it, one device at a time, until it starts rebooting, you then have identified the problematic device.

No one can give you any other helpful advice really without the above steps taken to find the cause, otherwise it's all guess work.

Good luck.

I see the suggestion of running out of NAT table space has already been mentioned, but also some routers can reboot if the line resync's - one reason I run a separate modem and router.

In the days of O2 and BeThere broadband, some people would choose a 3db margin and some modem/routers wouldn't cope with this and reboot when the SNRM dropped too low. They should have just caused a resync, but maybe the developer thought a reboot and a resync was the same thing !!