Created attachment 276401 [details] TCP Dump Hi, after a dist upgrade from Ubuntu 17.10 (Kernel 4.13.x) to Ubuntu 18.04 (Kernel 4.15.0) I suffer from ramdomly generated TCP RST packets sent (presumably) by the Kernel on a bonding device that uses bonding mode "brodcast" with 2 physical NICs. With tcpdump/whireshark I can see that the kernel randomly sends TCP-RST packets after the SYN/ACK/ACK packet is received (see attached PCAP). This only happens if the kernel receives the initial SYN packet on both physical NICs (and therefore seeing it twice), before the connection is established by sending SYN/ACK. It's not happening in 100% of all cases and only, if the system can use two or more CPU cores/threads. With only one CPU available to the system, this behaviour is not reproducable. I can reproduce this on multiple physical servers with 2 bonded Intel NICs connected over 2 seperate Switches and with virtual machines on a KVM Host using 2 dedicated host bridges. This also happens with a fresh installed Ubuntu 18.04 and Fedora 28 (kernel 4.16), so I decided to compile and boot with Kernel 4.17.0 on ubuntu, getting the same result. Only disabling/blocking the second network connection or reducing the amount of CPU cores of the VM to one core solves the problem, so I think this could be a race condition on systems with more than one CPU core and thread. For my tests I used a very basic Ubuntu 18.04 (x86-64) running xinetd tcp-echo service (port 7/TCP). On the client I used the netcat-traditional packet with the following command: while true; do echo $(date) | nc.traditional -q 1 ECHO-SERVER 7; sleep 0.1 ; done This gives the following output: --------------------------------------- Fr 8. Jun 09:12:43 UTC 2018 Fr 8. Jun 09:12:43 UTC 2018 Fr 8. Jun 09:12:43 UTC 2018 Fr 8. Jun 09:12:43 UTC 2018 Fr 8. Jun 09:12:43 UTC 2018 Fr 8. Jun 09:12:43 UTC 2018 Fr 8. Jun 09:12:43 UTC 2018 Fr 8. Jun 09:12:43 UTC 2018 (UNKNOWN) [192.168.86.101] 7 (echo) : Connection reset by peer (UNKNOWN) [192.168.86.101] 7 (echo) : Connection reset by peer (UNKNOWN) [192.168.86.101] 7 (echo) : Connection reset by peer Fr 8. Jun 09:12:44 UTC 2018 Fr 8. Jun 09:12:44 UTC 2018 Fr 8. Jun 09:12:44 UTC 2018 Fr 8. Jun 09:12:44 UTC 2018 Fr 8. Jun 09:12:44 UTC 2018 Fr 8. Jun 09:12:44 UTC 2018 Fr 8. Jun 09:12:44 UTC 2018 Fr 8. Jun 09:12:44 UTC 2018 Fr 8. Jun 09:12:44 UTC 2018 Fr 8. Jun 09:12:44 UTC 2018 (UNKNOWN) [192.168.86.101] 7 (echo) : Connection reset by peer (UNKNOWN) [192.168.86.101] 7 (echo) : Connection reset by peer Fr 8. Jun 09:12:44 UTC 2018 ---------------------------------------