Intel I211/82579LM NICs on Windows silently drop valid IPMI UDP packets due to a UDP Rx checksum offload bug; disabling IPv4 UDP Rx checksum offload fixes it.
Key Takeaways
PktMon, not Wireshark, revealed the drop reason: Windows TCP/IP stack flagged incoming UDP packets as having invalid checksums, even though software validation passed.
The Intel NIC hardware/driver marks valid UDP checksums as invalid for certain packets, likely triggered by the Tyan SMDC reusing the IP header ID field from incoming packets.
Disabling IPv4 UDP Rx checksum offload in the Intel NIC driver (e1r68x64.sys / e1i65x64.sys) resolves the issue without other side effects.
The bug is silent: DHCP and DNS work fine, so the offload failure only surfaces with specific edge-case UDP traffic like IPMI on port 623.
Some practitioners recommend disabling checksum offloading entirely, arguing diagnosis costs exceed any throughput gains when offloading misbehaves.
