-M option doesn't work

[Gunterwa]

192.168.3.26 is ptpmaster, it got multicast packets from ntpperf (192.168.3.57) and responsed, but it seemd the response msg were ignored by ntpperf..

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[Gunterwa]

ptpmaster response in the test are multicast, is it OK?

[mlichvar]

Multicast responses are ok. Are they coming from the address specified by the -d option?

Do you see both requests and responses in tcpdump and could you post few lines from the output showing at least one request and response?

[Gunterwa]

Delay_Response.pcapng.zip
Enclosed please find the pcap file, thanks for your great support.

[mlichvar]

It looks like there might be two issues. One is that the NIC could be filtering multicast traffic if there is nothing else using it. The other is your server seems to be using source port 319 even for general messages and not just event messages as is normally expected.

Please try it again with the current code in git.