2

I have a Pi 4 2gb model and am unable to get ethernet to work.

The Pi is able to connect to my network via Wi-Fi, however when the ethernet cord is plugged in I only receive a yellow light, no longer a green one. I have purchased new cables and tried existing ones with the same result.

I have tried refreshing the OS with Raspberry Pi OS 32 and 64 bit and also Ubuntu server 32 and 64 bit with the same results even after running sudo apt-get update/grade.

My current setup is the Pi plugged into an unmanaged switch connected to my Eero 6 pro. I have tried to reboot the network and pi several times to see if it would resolve the DHCP, but it doesn't seem to. I have two other Pi 3's that are able to connect fine over ethernet.

Edit: Here is my output from ifconfig:

pi@raspberrypi:~ $ ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 169.254.20.130  netmask 255.255.0.0  broadcast 169.254.255.255
        inet6 fe80::1494:366d:c316:229c  prefixlen 64  scopeid 0x20<link>
        ether dc:a6:32:2b:59:35  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 44  bytes 6653 (6.4 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 21  bytes 2490 (2.4 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 21  bytes 2490 (2.4 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

wlan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.6.248  netmask 255.255.252.0  broadcast 192.168.7.255
        inet6 fd30:fa95:3a35:47a0:82ff:1e06:493f:c4b1  prefixlen 64  scopeid 0x0<global>
        inet6 fe80::aed6:6252:ae7e:637e  prefixlen 64  scopeid 0x20<link>
        ether dc:a6:32:2b:59:36  txqueuelen 1000  (Ethernet)
        RX packets 1708  bytes 1438450 (1.3 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 508  bytes 51630 (50.4 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Edit: Output from ethtool eth0

pi@raspberrypi:~ $ ethtool eth0
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/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
    Auto-negotiation: on
    master-slave cfg: preferred slave
    master-slave status: slave
    Port: Twisted Pair
    PHYAD: 1
    Transceiver: external
    MDI-X: Unknown
netlink error: Operation not permitted
        Current message level: 0x00000007 (7)
                               drv probe link
    Link detected: yes
pi@raspberrypi:~ $ sudo ethtool eth0
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/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
    Auto-negotiation: on
    master-slave cfg: preferred slave
    master-slave status: slave
    Port: Twisted Pair
    PHYAD: 1
    Transceiver: external
    MDI-X: Unknown
    Supports Wake-on: d
    Wake-on: d
        Current message level: 0x00000007 (7)
                               drv probe link
    Link detected: yes

Other trouble shooting steps I have attempted was swapping the ethernet cable, connecting directly to the Eero router instead of a switch, new power supply, new SD card, new image.

dhcpcd.conf comparison: I compared the /etc/dhcpcd.conf files from the functional RPi 3B, and the non-functional RPi 4B: the files are identical.

Edit 2

Output from systemctl status dhcpdcd

pi@raspberrypi:~ $ sudo ethtool -s eth0 autoneg off
pi@raspberrypi:~ $ sudo ethtool -s eth0 speed 100
pi@raspberrypi:~ $ systemctl status dhcpcd
● dhcpcd.service - DHCP Client Daemon
     Loaded: loaded (/lib/systemd/system/dhcpcd.service; enabled; vendor preset: enabled)
     Active: active (running) since Fri 2023-02-17 07:32:59 CST; 2min 13s ago
       Docs: man:dhcpcd(8)
    Process: 371 ExecStart=/usr/sbin/dhcpcd -b -q (code=exited, status=0/SUCCESS)
   Main PID: 427 (dhcpcd)
      Tasks: 2 (limit: 3720)
        CPU: 956ms
     CGroup: /system.slice/dhcpcd.service
             ├─427 /usr/sbin/dhcpcd -b -q
             └─586 wpa_supplicant -B -c/etc/wpa_supplicant/wpa_supplicant.conf -iwlan0

Feb 17 07:33:13 raspberrypi dhcpcd[427]: eth0: adding route to 169.254.0.0/16
Feb 17 07:33:16 raspberrypi dhcpcd[427]: eth0: no IPv6 Routers available
Feb 17 07:34:46 raspberrypi dhcpcd[427]: wlan0: Router Advertisement from fe80::c35:8359:7092:e432
Feb 17 07:35:08 raspberrypi dhcpcd[427]: eth0: carrier lost
Feb 17 07:35:08 raspberrypi dhcpcd[427]: eth0: deleting address fe80::1494:366d:c316:229c
Feb 17 07:35:08 raspberrypi dhcpcd[427]: eth0: deleting route to 169.254.0.0/16
Feb 17 07:35:11 raspberrypi dhcpcd[427]: eth0: carrier acquired
Feb 17 07:35:11 raspberrypi dhcpcd[427]: eth0: IAID 32:2b:59:35
Feb 17 07:35:11 raspberrypi dhcpcd[427]: eth0: adding address fe80::1494:366d:c316:229c
Feb 17 07:35:12 raspberrypi dhcpcd[427]: eth0: soliciting a DHCP lease

Edit with updated output from ethtool eth0

pi@raspberrypi:~ $ sudo ethtool -s eth0 speed 100
pi@raspberrypi:~ $ sudo ethtool -s eth0 autoneg off
pi@raspberrypi:~ $ sudo ethtool eth0
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: No
    Advertised FEC modes: Not reported
    Speed: 100Mb/s
    Duplex: Full
    Auto-negotiation: off
    master-slave cfg: preferred slave
    master-slave status: slave
    Port: Twisted Pair
    PHYAD: 1
    Transceiver: external
    MDI-X: Unknown
    Supports Wake-on: d
    Wake-on: d
        Current message level: 0x00000007 (7)
                               drv probe link
    Link detected: yes

Edit with output from journalctl -u dhcpcd.service

-- Boot aaded611165044d9aa515c9641d89311 --
Feb 15 20:24:32 raspberrypi systemd[1]: Starting DHCP Client Daemon...
Feb 15 20:24:32 raspberrypi dhcpcd[368]: dev: loaded udev
Feb 15 20:24:33 raspberrypi dhcpcd[368]: forked to background, child pid 419
Feb 15 20:24:33 raspberrypi dhcpcd[419]: eth0: waiting for carrier
Feb 15 20:24:33 raspberrypi systemd[1]: Started DHCP Client Daemon.
Feb 15 20:24:34 raspberrypi dhcpcd-run-hooks[571]: wlan0: starting wpa_supplicant
Feb 15 20:24:35 raspberrypi dhcpcd[419]: wlan0: connected to Access Point `'
Feb 15 20:24:35 raspberrypi dhcpcd[419]: wlan0: waiting for carrier
Feb 15 20:24:37 raspberrypi dhcpcd[419]: eth0: carrier acquired
Feb 15 20:24:37 raspberrypi dhcpcd[419]: DUID 00:01:00:01:2a:be:6a:26:dc:a6:32:2b:59:35
Feb 15 20:24:37 raspberrypi dhcpcd[419]: eth0: IAID 32:2b:59:35
Feb 15 20:24:37 raspberrypi dhcpcd[419]: eth0: adding address fe80::1494:366d:c316:229c
Feb 15 20:24:37 raspberrypi dhcpcd[419]: eth0: soliciting an IPv6 router
Feb 15 20:24:38 raspberrypi dhcpcd[419]: eth0: soliciting a DHCP lease
Feb 15 20:24:40 raspberrypi dhcpcd[419]: wlan0: carrier acquired
Feb 15 20:24:40 raspberrypi dhcpcd[419]: wlan0: connected to Access Point `HomeKit'
Feb 15 20:24:40 raspberrypi dhcpcd[419]: wlan0: IAID 32:2b:59:36
Feb 15 20:24:40 raspberrypi dhcpcd[419]: wlan0: adding address fe80::aed6:6252:ae7e:637e
Feb 15 20:24:41 raspberrypi dhcpcd[419]: wlan0: rebinding lease of 192.168.6.248
Feb 15 20:24:41 raspberrypi dhcpcd[419]: wlan0: soliciting an IPv6 router
Feb 15 20:24:41 raspberrypi dhcpcd[419]: wlan0: probing address 192.168.6.248/22
Feb 15 20:24:42 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::1c5d:435c:40e2:b058
Feb 15 20:24:42 raspberrypi dhcpcd[419]: wlan0: adding address fd30:fa95:3a35:47a0:82ff:1e06:493f:c4b1/64
Feb 15 20:24:42 raspberrypi dhcpcd[419]: wlan0: adding route to fd30:fa95:3a35:47a0::/64
Feb 15 20:24:42 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::141c:f280:8b8f:eadd
Feb 15 20:24:42 raspberrypi dhcpcd[419]: wlan0: adding address fd30:fa95:3a35:47a0:82ff:1e06:493f:c4b1/64
Feb 15 20:24:42 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::10a4:7508:25d5:163a
Feb 15 20:24:42 raspberrypi dhcpcd[419]: wlan0: adding address fd30:fa95:3a35:47a0:82ff:1e06:493f:c4b1/64
Feb 15 20:24:42 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::10d9:826e:46df:b411
Feb 15 20:24:42 raspberrypi dhcpcd[419]: wlan0: adding address fd30:fa95:3a35:47a0:82ff:1e06:493f:c4b1/64
Feb 15 20:24:43 raspberrypi dhcpcd[419]: eth0: probing for an IPv4LL address
Feb 15 20:24:46 raspberrypi dhcpcd[419]: wlan0: leased 192.168.6.248 for 12372 seconds
Feb 15 20:24:46 raspberrypi dhcpcd[419]: wlan0: adding route to 192.168.4.0/22
Feb 15 20:24:46 raspberrypi dhcpcd[419]: wlan0: adding default route via 192.168.4.1
Feb 15 20:24:48 raspberrypi dhcpcd[419]: eth0: using IPv4LL address 169.254.20.130
Feb 15 20:24:48 raspberrypi dhcpcd[419]: eth0: adding route to 169.254.0.0/16
Feb 15 20:24:49 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::141c:f280:8b8f:eadd
Feb 15 20:24:51 raspberrypi dhcpcd[419]: eth0: no IPv6 Routers available
Feb 15 20:24:52 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::141c:f280:8b8f:eadd
Feb 15 20:26:22 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::10d9:826e:46df:b411
Feb 15 20:27:11 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::1c5d:435c:40e2:b058
Feb 15 20:27:26 raspberrypi dhcpcd[419]: wlan0: fe80::1c5d:435c:40e2:b058 is unreachable
Feb 15 20:27:26 raspberrypi dhcpcd[419]: wlan0: fe80::10a4:7508:25d5:163a is unreachable
Feb 15 20:27:26 raspberrypi dhcpcd[419]: wlan0: fe80::141c:f280:8b8f:eadd is unreachable
Feb 15 20:27:26 raspberrypi dhcpcd[419]: wlan0: fe80::10d9:826e:46df:b411 is unreachable
Feb 15 20:27:26 raspberrypi dhcpcd[419]: wlan0: carrier lost
Feb 15 20:27:26 raspberrypi dhcpcd[419]: wlan0: deleting address fd30:fa95:3a35:47a0:82ff:1e06:493f:c4b1/64
Feb 15 20:27:26 raspberrypi dhcpcd[419]: wlan0: deleting route to fd30:fa95:3a35:47a0::/64
Feb 15 20:27:26 raspberrypi dhcpcd[419]: wlan0: deleting address fe80::aed6:6252:ae7e:637e
Feb 15 20:27:26 raspberrypi dhcpcd[419]: eth0: adding default route
Feb 15 20:27:26 raspberrypi dhcpcd[419]: wlan0: deleting route to 192.168.4.0/22
Feb 15 20:27:26 raspberrypi dhcpcd[419]: wlan0: deleting default route via 192.168.4.1
Feb 15 20:28:20 raspberrypi dhcpcd[419]: wlan0: carrier acquired
Feb 15 20:28:20 raspberrypi dhcpcd[419]: wlan0: IAID 32:2b:59:36
Feb 15 20:28:20 raspberrypi dhcpcd[419]: wlan0: adding address fe80::aed6:6252:ae7e:637e
Feb 15 20:28:20 raspberrypi dhcpcd[419]: wlan0: soliciting an IPv6 router
Feb 15 20:28:20 raspberrypi dhcpcd[419]: wlan0: rebinding lease of 192.168.6.248
Feb 15 20:28:20 raspberrypi dhcpcd[419]: wlan0: probing address 192.168.6.248/22
Feb 15 20:28:26 raspberrypi dhcpcd[419]: wlan0: leased 192.168.6.248 for 12167 seconds
Feb 15 20:28:26 raspberrypi dhcpcd[419]: wlan0: adding route to 192.168.4.0/22
Feb 15 20:28:26 raspberrypi dhcpcd[419]: wlan0: adding default route via 192.168.4.1
Feb 15 20:28:26 raspberrypi dhcpcd[419]: eth0: deleting default route
Feb 15 20:28:40 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::10d9:826e:46df:b411
Feb 15 20:28:45 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::141c:f280:8b8f:eadd
Feb 15 20:28:45 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::10a4:7508:25d5:163a
Feb 15 20:28:47 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::1c5d:435c:40e2:b058
Feb 15 20:29:06 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::10d9:826e:46df:b411
Feb 15 20:29:06 raspberrypi dhcpcd[419]: wlan0: adding address fd30:fa95:3a35:47a0:82ff:1e06:493f:c4b1/64
Feb 15 20:29:06 raspberrypi dhcpcd[419]: wlan0: adding route to fd30:fa95:3a35:47a0::/64
Feb 15 20:29:12 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::10a4:7508:25d5:163a
Feb 15 20:29:12 raspberrypi dhcpcd[419]: wlan0: adding address fd30:fa95:3a35:47a0:82ff:1e06:493f:c4b1/64
Feb 15 20:29:13 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::1c5d:435c:40e2:b058
Feb 15 20:29:13 raspberrypi dhcpcd[419]: wlan0: adding address fd30:fa95:3a35:47a0:82ff:1e06:493f:c4b1/64
Feb 15 20:29:15 raspberrypi dhcpcd[419]: wlan0: Router Advertisement from fe80::141c:f280:8b8f:eadd
Feb 15 20:29:15 raspberrypi dhcpcd[419]: wlan0: adding address fd30:fa95:3a35:47a0:82ff:1e06:493f:c4b1/64
Feb 15 20:30:32 raspberrypi dhcpcd[419]: received SIGTERM, stopping
Feb 15 20:30:32 raspberrypi dhcpcd[419]: wlan0: removing interface
Feb 15 20:30:32 raspberrypi dhcpcd[419]: eth0: adding default route
Feb 15 20:30:32 raspberrypi dhcpcd[419]: eth0: removing interface
Feb 15 20:30:32 raspberrypi systemd[1]: Stopping DHCP Client Daemon...
Feb 15 20:30:32 raspberrypi dhcpcd[419]: dhcpcd exited
Feb 15 20:30:33 raspberrypi systemd[1]: dhcpcd.service: Succeeded.
Feb 15 20:30:33 raspberrypi systemd[1]: Stopped DHCP Client Daemon.
Feb 15 20:30:33 raspberrypi systemd[1]: dhcpcd.service: Consumed 2.516s CPU time.
-- Boot 23a1ec119b3c4936ad87c7eccdfd0f57 --

-- Boot 4046619d8227446c89bc72cb023aec2e --
Feb 18 23:42:42 raspberrypi dhcpcd[428]: wlan0: Router Advertisement from fe80::10d9:826e:46df:b411
Feb 18 23:43:52 raspberrypi dhcpcd[428]: wlan0: Router Advertisement from fe80::c35:8359:7092:e432
Feb 18 23:45:14 raspberrypi dhcpcd[428]: wlan0: Router Advertisement from fe80::18c0:858b:dd40:dfea
Feb 18 23:45:28 raspberrypi dhcpcd[428]: wlan0: Router Advertisement from fe80::141c:f280:8b8f:eadd
Feb 18 23:47:41 raspberrypi dhcpcd[428]: eth0: carrier lost
Feb 18 23:47:41 raspberrypi dhcpcd[428]: eth0: deleting address fe80::1494:366d:c316:229c
Feb 18 23:47:41 raspberrypi dhcpcd[428]: eth0: deleting route to 169.254.0.0/16
Feb 18 23:47:44 raspberrypi dhcpcd[428]: eth0: carrier acquired
Feb 18 23:47:44 raspberrypi dhcpcd[428]: eth0: IAID 32:2b:59:35
Feb 18 23:47:44 raspberrypi dhcpcd[428]: eth0: adding address fe80::1494:366d:c316:229c
Feb 18 23:47:44 raspberrypi dhcpcd[428]: eth0: soliciting an IPv6 router
Feb 18 23:47:45 raspberrypi dhcpcd[428]: eth0: soliciting a DHCP lease
Feb 18 23:47:50 raspberrypi dhcpcd[428]: eth0: probing for an IPv4LL address
Feb 18 23:47:55 raspberrypi dhcpcd[428]: eth0: using IPv4LL address 169.254.20.130
Feb 18 23:47:55 raspberrypi dhcpcd[428]: eth0: adding route to 169.254.0.0/16
Feb 18 23:47:57 raspberrypi dhcpcd[428]: eth0: no IPv6 Routers available
3
  • I have updated my original post with more information @Milliways
    – KingVMP
    Commented Feb 17, 2023 at 4:46
  • @Milliways I have updated the original post with the output of the command. I am not using a Cat6 cable, but will purchase one later today from BestBuy.
    – KingVMP
    Commented Feb 17, 2023 at 13:37
  • I have updated the post with the output of the command after running those two commands, and ethernet is still just showing link. @Milliways
    – KingVMP
    Commented Feb 19, 2023 at 5:53

3 Answers 3

1

From the ifconfig output you provided, it's possible you've mis-configured something in your /etc/dhcpcd.conf file; have you made any changes to this file?

Why do I say this?

Because:

eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 inet 169.254.20.130 ...

This is a Link-Local address, and that suggests your RPi may be unable to reach a DHCP server.

OTOH your wlan0 shows an IP of 192.168.6.248 - suggesting the presence of a DHCP, but on a different network. Maybe I assume too much, but I'll guess that this was not the intended network configuration. Mis-configured /etc/dhcpcd.conf files are a frequent source of error.

So, a first step is to clear any potential mis-configuration in /etc/dhcpcd.conf. If you've made any edits, please post them by adding the file contents to your question.

Milliways suggestion in the comment is a good one:

From your shell's command line, enter this:

$ ethtool eth0 

Review the output (or add it to your question via an edit) for anything suspicious. In particular, the line Link detected: should be followed by Yes if you're plugged into your router.

9
  • > From the ifconfig output you provided, it's possible you've mis-configured something in your /etc/dhcpcd.conf file; have you made any changes to this file? This is a fresh install from the imager, ethernet used to work but didn't once I decided to refresh my card. > This is my output from ethanol eth0 pastebin.com/9P937kgs
    – KingVMP
    Commented Feb 17, 2023 at 4:40
  • @KingVMP: No diffs in dhcpcd.conf, ethtool reports a link. Are both RPi connected to the same switch? Do they both use the same DHCP server? IOW, the problem appears to be upstream from your RPi.
    – Seamus
    Commented Feb 17, 2023 at 5:03
  • Yes, both pi's are connected to the same switch and there is only one DHCP server on the network. The yellow light on the pi shows, but the green doesn't. The ethernet used to work, but no longer does after a fresh-install. I never had to do anything special previously to get it running; was always plug and play.
    – KingVMP
    Commented Feb 17, 2023 at 5:23
  • @KingVMP: I'm stumped for now... let me think on it. In the meantime, Milliways has just updated his answer, so try that. One other question for you: Has this Pi 4 ever successfully worked with eth0??
    – Seamus
    Commented Feb 17, 2023 at 7:29
  • @KingVMP: They say that "misery loves company", so you may find solace in this :) Rebooting can be a game changer! The switch and the router.
    – Seamus
    Commented Feb 17, 2023 at 8:02
0

I suspect your switch or router do not support Gigabit Ethernet. (It is also possible the Ethernet connector or cable is damaged or does not support Gigabit Ethernet.)

See https://raspberrypi.stackexchange.com/a/112682/8697

Try the following and see what happens.

sudo ethtool -s eth0 autoneg off
sudo ethtool -s eth0 speed 100
5
  • The "Link Partner" advertises 1000baseT/Full
    – Seamus
    Commented Feb 17, 2023 at 8:06
  • There is a bug in the Ethernet negotiation protocol. All negotiation happens over 2 pair but if there aren't 4 working pair actual connection fails.
    – Milliways
    Commented Feb 17, 2023 at 8:52
  • So - you suspect a bad cable? I do seem to recall having been through something similar to this once... Troubleshooting was a PITA; I was lucky enough to find some decent documentation.
    – Seamus
    Commented Feb 17, 2023 at 9:49
  • @Seamus I have a number of theories. I prefer to analyse the problem before suggesting solutions. As an engineering manager I spent lots of time stopping young engineers from jumping into solution mode BEFORE they had investigated the problem.
    – Milliways
    Commented Feb 17, 2023 at 10:50
  • Good for you - a confucian approach.
    – Seamus
    Commented Feb 18, 2023 at 5:20
0

Both interfaces are advertising support for 1000BaseT. However, while 100BaseT and below only need two pairs in the ethernet cable, 1000BaseT needs all four.

I have noticed that when my cable only had two pairs connected, that ethtool output still showed both ends advertising 1000BaseT. So the interfaces do not check the cable before deciding what to advertise. I also see the same when using my POE adapter.

So you need to have a careful look at what is connecting the two ports together. Your mention you have tried several cables so you have to have a look at sockets.

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