Re: [Intel-wired-lan] Fw: [Bug 221750] New: igc: Intel I225 silently drops UDP broadcast to port 68 (DHCP) when interface is a bridge member

["Ruinskiy, Dima" <dima.ruinskiy@intel.com>]

On 22/07/2026 18:46, Stephen Hemminger wrote:
> Linux networking does not really use bugzilla, instead use email.
> 
> $ ./scripts/get_maintainer.pl drivers/net/ethernet/intel/igc
> Tony Nguyen <anthony.l.nguyen@intel.com> (maintainer:INTEL ETHERNET DRIVERS)
> Przemek Kitszel <przemyslaw.kitszel@intel.com> (maintainer:INTEL ETHERNET DRIVERS)
> Andrew Lunn <andrew+netdev@lunn.ch> (maintainer:NETWORKING DRIVERS)
> "David S. Miller" <davem@davemloft.net> (maintainer:NETWORKING DRIVERS)
> Eric Dumazet <edumazet@google.com> (maintainer:NETWORKING DRIVERS)
> Jakub Kicinski <kuba@kernel.org> (maintainer:NETWORKING DRIVERS)
> Paolo Abeni <pabeni@redhat.com> (maintainer:NETWORKING DRIVERS)
> intel-wired-lan@lists.osuosl.org (moderated list:INTEL ETHERNET DRIVERS)
> netdev@vger.kernel.org (open list:NETWORKING DRIVERS)
> 
> 
> Begin forwarded message:
> 
> Date: Mon, 13 Jul 2026 16:20:22 +0000
> From: bugzilla-daemon@kernel.org
> To: stephen@networkplumber.org
> Subject: [Bug 221750] New: igc: Intel I225 silently drops UDP broadcast to port 68 (DHCP) when interface is a bridge member
> 
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=221750
> 
>              Bug ID: 221750
>             Summary: igc: Intel I225 silently drops UDP broadcast to port
>                      68 (DHCP) when interface is a bridge member
>             Product: Networking
>             Version: 2.5
>            Hardware: Intel
>                  OS: Linux
>              Status: NEW
>            Severity: normal
>            Priority: P3
>           Component: Other
>            Assignee: stephen@networkplumber.org
>            Reporter: eslopez92@gmail.com
>          Regression: No
> 
> ## Description
> 
> When an Intel I225-LM NIC using the igc driver is added as a member of a Linux
> bridge, UDP broadcast packets with destination port 68 (DHCP client port) are
> silently dropped at the TX path. The kernel queues the packet for transmission
> (visible via AF_PACKET capture on the interface showing PACKET_OUTGOING), but
> the frame never appears on the physical wire.
> 
> All other UDP broadcast ports (e.g., port 9998) transmit correctly through the
> same bridge, same interface, same code path. Only destination port 67/68 (DHCP)
> is affected.
> 
> This breaks any DHCP server (e.g., dnsmasq) running on the bridge host, as DHCP
> offers never reach clients.
> 
> ### Keywords
> 
> igc, I225, bridge, DHCP, broadcast, TX drop, dnsmasq
> 
> ### Kernel version
> 
>      Linux version 6.8.0-134-generic (Ubuntu 24.04)
>      Also tested: 6.17.0-35-generic (Ubuntu 24.04 HWE) - same behavior
> 
> ### How to reproduce
> 
> 1. System: Supermicro X13SAZ-F with Intel I225-LM (PCI 8086:15f2), igc driver
> 2. Create a Linux bridge and enslave the igc interface:
> 
>          ip link add br-fvn type bridge
>          ip link set eno1 master br-fvn
>          ip addr add 172.31.0.3/16 dev br-fvn
>          ip link set br-fvn up
> 
> 3. Run dnsmasq as DHCP server on br-fvn:
> 
>          dnsmasq --interface=br-fvn
> --dhcp-range=172.31.100.1,172.31.254.255,255.255.0.0,12h --dhcp-authoritative
> 
> 4. Connect a DHCP client to eno1 (directly or via switch)
> 5. Observe: dnsmasq logs show DHCPDISCOVER received and DHCPOFFER sent, but the
> client never receives the offer
> 
> ### Verification that the bug is interface-specific
> 
> - Replacing eno1 (igc, I225-LM) with a USB ethernet adapter (r8152, RTL8153) in
> the same bridge: DHCP works immediately
> - Using an Intel I210 NIC (igb driver) in the same bridge on identical kernel:
> DHCP works
> - Sending UDP broadcast to port 9998 from the same bridge via the same igc
> interface: packets arrive at client
> - Sending UDP broadcast to port 68 from the same bridge via the same igc
> interface: packets never arrive
> - AF_PACKET raw capture on eno1 (host side) shows the DHCP offer as
> PACKET_OUTGOING (type=4), confirming the kernel hands it to the driver, but the
> frame never hits the wire
> - Wireshark/tcpdump on the client confirms zero DHCP offers received
> 
> ### Environment
> 
>      Processor: Intel Core i9-14900K
>      Board: Supermicro X13SAZ-F
>      NIC: Intel I225-LM (8086:15f2, subsystem 15d9:15f2)
>      Driver: igc
>      Firmware: 1073:8754
>      Bus: 0000:01:00.0 (PCIe x1, 5.0 GT/s)
>      OS: Ubuntu Core 24 (snap-based)
> 
> ### Other notes
> 
> - ethtool -K br-fvn tx-checksum-ip-generic off was tested - no change
> - bridge-nf-call-iptables=0 was tested - no change
> - br_netfilter module unloaded - no change
> - net.ipv4.ip_forward=1 was tested - no change
> - No iptables, nftables, or ebtables rules present
> - No eBPF/XDP programs attached
> - The igb driver (Intel I210) does NOT exhibit this behavior on the same kernel
> 

Thank you for the detailed analysis and information.
I've done some digging and it looks like an issue that has been fixed in 
firmware.
Your environment shows I225-LM Firmware: 1073:8754 which indicates 
version 1.73. I believe the fix to be available starting from version 1.91.
It may require an update to the AMT FW as well.
Both should be distributed by the motherboard vendor. I suggest to 
inquire with Supermicro whether they have a FW update for your device. 
It may be included in the full BIOS/BMC/Bundle that they offer.

--Dima