Intel NIC UDP Checksum Offloading Causes IPMI Packet Loss on Windows 11

On May 4, 2026, Michal Necasek documented a networking anomaly where Windows 11 machines failed to receive IPMI UDP packets from a Tyan SMDC module, despite the packets arriving on the network. The issue manifested as a DropReason INET: checksum is invalid reported by PktMon, while Wireshark and Linux ipmitool confirmed the checksums were correct. The culprit was identified as the Intel I211 NIC driver (e1r68x64.sys) on Windows 11 and the Intel 82579LM driver (e1i65x64.sys) on Windows 10, both performing faulty IPv4 UDP receive checksum offloading. Disabling the IPv4 UDP Rx checksum offload flag in the respective driver configuration restored IPMI communication for both the host and its VMs. The problem did not appear on a Windows 10 laptop with a Killer Wireless 1525 adapter, nor did it affect DHCP or DNS, indicating the issue is isolated to specific Intel NICs. Linux, even with the same hardware, accepted the packets without modification, confirming the driver’s checksum logic is at fault. The author speculates that the NIC’s handling of the IP Packet ID field and lack of DF flag in outgoing packets may trigger the incorrect checksum validation. The practical fix is to turn off IPv4 UDP Rx checksum offloading on affected Intel NICs, a workaround that avoids the need for driver updates.