Capturing autonegotiation possible?

Hardware Questions and Recommendations
1

Hi,

I have little problem with my home setup and want to try to figure out which part is the problem.

My setup looks like following:
ISP --> Fritzbox(provides Wlan and own subnet) --> OpenWRT(also provides it own Wlan and subnet)

Now my problem is that my fritzbox and my OpenWRT router set there ethernet speed to 1Gbit/s if i plug in the RJ45 cable thats the normal behavior, but after some hours it is set to 100Mbit/s, instead of unplug my cable(cause of lazyness) I force the fritzbox with the webui to set it on 100Mbit/s and re-set it to 1Gbit/s, that also solves the problem but if I have to do this multiple times a day it is not very amusing. OpenWRT and fritzbox are connected with a 3 year old cat 7 cable.
In my fritzbox I don't have settings like engery save mode or green mode.

And now finally the question, is it possible to capture(tcpdump or something else) if the fritzbox send something like re-autonegotiation and handles it to 100Mbit/s cause of inactivity or something else?

Regards
lucki1000

2

You may be able to see the negotiation results (but not likely the underlying information) in the standard syslog.

Have you tried replacing the cable?

3

Tried forcing 1gbit, and disabling autoneg using ethtool?

4
  • are there any 10/100 MBit/s devices connected directly (not through an intermediary -external- switch) to your OpenWrt router?
  • please check the connectors and sockets between your f!b and the OpenWrt router for damage/ benting pins or dirt/ debris
  • if reasonably possible, please test a different cable between them
5

I thought about that too, but I want to delay it, because I would have to buy a new one.

Thanks for your answer.

6

Yes, I tried with this command:

ethtool -s eth0.2 autoneg off speed 1000 duplex full
Cannot set new settings: Not supported
  not setting speed
  not setting duplex
  not setting autoneg

but I guess i doesn't work on VLANs, and on eth0 it has no noticeable effect, the speed is unchanged.

7

For testing (confirming the cause), it might be sufficient to place both devices next to each other and to use a short cable (e.g. over night), to see what's happening.

8

Hi guys,

it really seems that the cable is the problem.

Thank you guys for help.

9

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