1

I have this setup:

A router in my living room that "feeds" all internet plugs. In my office the LAN connection works correctly with my PC and PS4 but my Raspi 4 does not detect any signal. However, if I connect the same Raspi 4 directly to the router through LAN, it works fine. In all experiences I have used the same cables.

What could be the source of the problem?

EDIT:

Not working ethtool eth0 log:

Settings for eth0:
        Supported ports: [ TP MII ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Half 1000baseT/Full
        Supported pause frame use: Symmetric Receive-only
        Supports auto-negotiation: Yes
        Supported FEC modes: Not reported
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Half 1000baseT/Full
        Advertised pause frame use: Symmetric Receive-only
        Advertised auto-negotiation: Yes
        Advertised FEC modes: Not reported
        Link partner advertised link modes:  10baseT/Half 10baseT/Full
                                             100baseT/Half 100baseT/Full
                                             1000baseT/Half 1000baseT/Full
        Link partner advertised pause frame use: Symmetric
        Link partner advertised auto-negotiation: Yes
        Link partner advertised FEC modes: Not reported
        Speed: 1000Mb/s
        Duplex: Full
        Port: MII
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: on
        Current message level: 0x00000007 (7)
                               drv probe link
        Link detected: no

Working ethtool eth0 log:

Settings for eth0:
        Supported ports: [ TP MII ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Half 1000baseT/Full
        Supported pause frame use: Symmetric Receive-only
        Supports auto-negotiation: Yes
        Supported FEC modes: Not reported
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Half 1000baseT/Full
        Advertised pause frame use: Symmetric Receive-only
        Advertised auto-negotiation: Yes
        Advertised FEC modes: Not reported
        Link partner advertised link modes:  10baseT/Half 10baseT/Full
                                             100baseT/Half 100baseT/Full
                                             1000baseT/Half 1000baseT/Full
        Link partner advertised pause frame use: Symmetric
        Link partner advertised auto-negotiation: Yes
        Link partner advertised FEC modes: Not reported
        Speed: 1000Mb/s
        Duplex: Full
        Port: MII
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: on
        Current message level: 0x00000007 (7)
                               drv probe link
        Link detected: yes
8
  • To clarify: you have an internet router in your living room without WiFi, all devices are connected by wire. All devices in the living room, connected to it, are working including the RasPi. There are several ethernet cables from the internet router in the living room to your office. Devices in your office connected by wire to the internet router are working well, except the RasPi. Can you confirm this?
    – Ingo
    May 21 '20 at 21:26
  • Router has wifi, but I don't use it in the office because of the low signal. There is only one cable from the router to the office that goes through the walls
    – Miguel
    May 21 '20 at 23:20
  • It is likely your wiring is NOT to Gigabit Ethernet standards. Post the output of ethtool eth0 (both working and not)
    – Milliways
    May 21 '20 at 23:48
  • "Router has wifi, but I don't use it in the office" - do you use it in the living room? There is only one ethernet cable to the office. Then you plug in there the PC, the PS4 and the RasPi one after the other. PC and PS4 are working on this cable but not the RasPi. Is this correct?
    – Ingo
    May 21 '20 at 23:52
  • Ok, I just edited the question and posted the log ethtool eth0. Yes, wifi is fine. PC and PS4 are not after the other. It is just one cable to I use to PC and PS4. To sum up: the same cable in the office works in PC and PS4 but does not in Raspi. But the Raspi works ok when connected directly to the router.
    – Miguel
    May 22 '20 at 0:02
2

The Pi4 (and Pi3B+) has a Gigabit Ethernet interface. To work this requires 4 pair high quality cabling.

Earlier models used 100baseT/Full which works on only 2 pair. Unfortunately, while the interface SHOULD negotiate a compatible mode the autonegotiation operates on 2 pair, so if both ends support Gigabit Ethernet this will be selected, even though the cabling does not support it.

You can downscale the link speed with ethtool commands. I have done this in the past, and the following should work, but I am not exactly sure of the syntax and order of commands.

sudo ethtool -s eth0 autoneg off
sudo ethtool -s eth0 speed 100

This should allow your Ethernet to work at a theoretically slower 100MBPS speed, but it is doubtful that you would notice.

2
  • Thanks! Your solutions worked right after the commands were executed. So this means that my cable connection is working with 2 pairs only?
    – Miguel
    May 22 '20 at 8:05
  • 1
    @Miguel all you can conclude is that the 4 pair are not working. I once had problems when my daughter's cat gnawed an Ethernet connector, some office cabling used some wires for telephone connection and only had 6 wires
    – Milliways
    May 22 '20 at 9:48
-1

Try plugging the pi into the router port that feeds your office jack. If that works then you've probably got a cable issue. If it doesn't work, what config is that port? speed/duplex , negotiation etc. Also, are there any entries in syslog in the scenario that doesn't work?

3
  • I did that. When I plug Raspi through LAN directly to the router (the same that feeds the office jack) it works fine.
    – Miguel
    May 21 '20 at 23:22
  • what about my other questions, re: log entries, anything? You have a cable tester?
    – myT250
    May 21 '20 at 23:34
  • I don't have a cable tester. I just posted the logs of ethtool eth0 as suggested.
    – Miguel
    May 22 '20 at 0:04

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