Created attachment 273645 [details] information of log messages, kernel version, nic driver version I use Intel 1G and 10G ethernet card with openvswitch under vxlan overlay network. Some VM started to use ECN and I found weird logs were generated about non-ECT. I analyzed vxlan packets, but all packets had no errors. Also, vxlan outer header's ECN was normal acording to RFC6040. I changed ethernet card from Intel's 1G/10G NIC (ixgbe and igb driver) to Broadcom's 1G/10G (tg3 and bnx2x driver), and I found there was no non-ECT log. So I guess this problem comes from ixgbe or igb driver. https://github.com/torvalds/linux/blob/master/drivers/net/vxlan.c#L1320 https://github.com/torvalds/linux/blob/master/include/net/inet_ecn.h#L186 I contaced to Intel support community, but they recommended to contact HP first. https://communities.intel.com/thread/120521 And I contacted to HP, but they guess this problem comes from OS. So I post this problem to bugzilla. Please see attached file.