Ethernet link is flapping constantly

[mdenes95]

I recently got my JetKVM unit, but seems like it has a bad ethernet port. It cannot keep an active ethernet link up for more than two seconds.
The screen on it works and also recognizes usb and hdmi signal, but the ethernet link never gets permanently active. Already contacted support via email, and ended up here. To me this seems like a hardware issue with the ethernet controller, but if there is a software fix for this issue i'm happy to try it out.

Connecting the ethernet link and usb to the same computer gets this dmesg output:

[11796.048783] usb 3-1: new high-speed USB device number 9 using xhci_hcd
[11796.236514] usb 3-1: New USB device found, idVendor=1d6b, idProduct=0044, bcdDevice= 0.40
[11796.236523] usb 3-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[11796.236529] usb 3-1: Product: JetKVM USB Emulation Device
[11796.236533] usb 3-1: Manufacturer: JetKVM
[11796.236538] usb 3-1: SerialNumber: ................
[11796.244989] input: JetKVM JetKVM USB Emulation Device as /devices/pci0000:00/0000:00:01.3/0000:02:00.2/0000:03:00.0/0000:04:00.0/usb3/3-1/3-1:1.0/0003:1D6B:0044.0016/input/input43
[11796.332944] hid-generic 0003:1D6B:0044.0016: input,hidraw5: USB HID v1.01 Keyboard [JetKVM JetKVM USB Emulation Device] on usb-0000:04:00.0-1/input0
[11796.333873] input: JetKVM JetKVM USB Emulation Device as /devices/pci0000:00/0000:00:01.3/0000:02:00.2/0000:03:00.0/0000:04:00.0/usb3/3-1/3-1:1.1/0003:1D6B:0044.0017/input/input44
[11796.334068] hid-generic 0003:1D6B:0044.0017: input,hidraw6: USB HID v1.01 Mouse [JetKVM JetKVM USB Emulation Device] on usb-0000:04:00.0-1/input1
[11796.334361] usb-storage 3-1:1.2: USB Mass Storage device detected
[11796.334583] scsi host9: usb-storage 3-1:1.2
[11797.258325] igb 0000:05:00.0 enp5s0: igb: enp5s0 NIC Link is Up 100 Mbps Full Duplex, Flow Control: RX/TX
[11797.380177] scsi 9:0:0:0: CD-ROM            JetKVM V irtual Media          PQ: 0 ANSI: 2
[11797.380657] sr 9:0:0:0: Power-on or device reset occurred
[11797.487735] sr 9:0:0:0: [sr0] scsi-1 drive
[11797.488853] sr 9:0:0:0: Attached scsi CD-ROM sr0
[11797.489070] sr 9:0:0:0: Attached scsi generic sg3 type 5
[11798.067924] igb 0000:05:00.0 enp5s0: igb: enp5s0 NIC Link is Down
[11799.893308] igb 0000:05:00.0 enp5s0: igb: enp5s0 NIC Link is Up 100 Mbps Full Duplex, Flow Control: RX/TX
[11800.685905] igb 0000:05:00.0 enp5s0: igb: enp5s0 NIC Link is Down
[11802.438290] igb 0000:05:00.0 enp5s0: igb: enp5s0 NIC Link is Up 100 Mbps Full Duplex, Flow Control: RX/TX
[11803.303878] igb 0000:05:00.0 enp5s0: igb: enp5s0 NIC Link is Down
[11804.957269] igb 0000:05:00.0 enp5s0: igb: enp5s0 NIC Link is Up 100 Mbps Full Duplex, Flow Control: RX/TX
[11805.791855] igb 0000:05:00.0 enp5s0: igb: enp5s0 NIC Link is Down
[11807.445240] igb 0000:05:00.0 enp5s0: igb: enp5s0 NIC Link is Up 100 Mbps Full Duplex, Flow Control: RX/TX
[11808.278840] igb 0000:05:00.0 enp5s0: igb: enp5s0 NIC Link is Down
...

What have i tried to fix this problem:

• Different ethernet cable
• Different USB cable
• Powering the device from a usb charger
• Powering the device with the included usb-c splitter
• Re-flashing the unit
• Connected via ethernet to multiple pc's / routers

[avegy]

Could this be an IP address conflict causing it to flap?

[mdenes95]

Could this be an IP address conflict causing it to flap?

No, the kvm never gets any ip address, because the link never stays up long enough to get address via dhcp. Also i tried using my pc as a dhcp server for the kvm, but never got any address assigned to it. And in that case the kvm would be the only one client on that network.

[mdenes95]

I managed to test the device on a managed switch, and forcing the ethernet link speed to 10 mbit/s seems that the problem goes away. The soon as i put it back on 100 mbit/s the link starts flapping again.
Also tried different duplex settings, with full duplex it works fine, with half duplex the link is completely gone.