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Ethernet Products
Determine ramifications of Intel® Ethernet products and technologies
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I226-LM won't send DHCPOFFER?

tblancher
Beginner
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I ran into a problem where the I226-LM NIC will not send the DHCPOFFER on the wire.  The strange thing is I can see in tcpdump that the DHCPOFFER should go out, but the clients never receive it.

 

After some searching, I discovered this may be a function of vPro Essentials enabled on the I226-LM NIC.  I haven't tried disabling AMT for this NIC in the BIOS, but that is one suggested workaround.  I've also seen that this does not always solve the problem.  It seems to only affect untagged or default VLAN traffic;  if other VLANs are configured it seems to work fine (I can corroborate this because I had other VLANs that the clients could definitely receive the DHCPOFFER).

 

I'm using Arch Linux on a SimplyNUC Onyx Pro, with two Intel 2.5GbE Ethernet ports:

  • 57:00.0 Ethernet controller: Intel Corporation Ethernet Controller I226-V (rev 04)
    Subsystem: Intel Corporation Device 0000
    Kernel driver in use: igc
    Interface name:  enp87s0
  • 58:00.0 Ethernet controller: Intel Corporation Ethernet Controller I226-LM (rev 04)
    Subsystem: Intel Corporation Device 0000
    Kernel driver in use: igc
    Interface name:  enp88s0

 

Some of the other posts I've seen linked show both Windows and pfSense (based on FreeBSD) and Proxmox have seen similar behavior.  See the Reddit/Netgate forums in the Arch Linux BBS topic I've been seeking help on for details.

 

Is this a known issue for my revision?  Do I need to go to my OEM (SimplyNUC) for a fix?  I want to be able to tell them what's going on, before I seek an AMI BIOS/UEFI update.

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tblancher
Beginner
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I reached out to my OEM, and they confirmed Intel is aware of the bug, and will be addressing it in a future firmware update.

 

The executive summary of the root cause is:  the I226-LM is misinterpreting the DHCPOFFER as an AMT control packet, so it consumes it before actually sending it on the wire.  This is below the Linux kernel level, so the system has no idea that the DHCPOFFER wasn't sent to the client.

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Adrianh85
Beginner
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In my troubleshooting using windows as working platform (with or without this workaround) and Proxmox being my problem area; I found that removing the M.2 on the chipset (not the one connected to CPU) activated the full functions of the I226LM on my Asus W680 board.

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jonmchan
Beginner
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I can confirm this bug affects the Asus W680M-ACE SE as well. I am running proxmox and all traffic from VMs sending DHCPOFFER are not properly sent. For my system, I was able to successfully get this to work by using the other NIC. I do not know why, but the bug was only affecting the "enp3s0" (physically bottom port) and not "enp4s0" (physically top port).

 

03:00.0 Ethernet controller: Intel Corporation Ethernet Controller I226-LM (rev 06)
04:00.0 Ethernet controller: Intel Corporation Ethernet Controller I226-LM (rev 06)

 

I will try the workarounds listed. Hopefully the bios update will be out soon.

 

UPDATE: I tried to disable AMT from the BIOS. I either could not find the right settings or none of the settings that I used made any difference. The only thing that consistently worked for me is to use the top port and not the lower intel NIC port.

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