Why vyos do the fragmentation even DF is marked



I’m experiencing weird thing in Vyos 1.1.17, I tried to do performance test with iperf on Vyos, and generated packets with length which exceeds the MTU in my environment and packets are marked as DF(Don’t Fragment), I expected that the traffic can’t be sent and PMTU discovery message is received. But surprisingly, the traffic reached the destination. I captured the packet with tcpdump and found that even packet is marked with DF, but it’s still fragmented. I tried it on the normal linux like ubuntu 16.04, it’s not gonna happen by default settings.

I wonder if VYOS(1.1.17) changed something which lead to this abnormal behavior? if you know the reason, could you please share what the change is? thanks in advance.

best regards.