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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
Miguel
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2 Answers2

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.

Milliways
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-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?

myT250
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