I cannot figure out, how can I turn off idenfification and the don’t fragment flag that I see in Wireshark in the RTP analysis. Also, in the trace I have header validation disabled. Can I enable it?
Don’t fragment is an IP flag, not an RTP one. On modern system it would be set by the OS, not the application, as part of path MTU discovery.
I can’t find any flag called identification for RTP. I can find an identification field, but not a flag, for IP, but that would be controlled by the OS.
What is your real problem?
There is some misconfiguration in my asterisk. I have set all quality settings like those of the peer. Audio and Sip QoS and ToS are now the same, and this has solved part of the problems. We have a Cisco router with a different sip ToS setting. Ping is prohibited. There is something else in the asterisk setup I cannot understand what leads to packet loss. The incoming traffic is OK, but the outgoing suffers. I have decided to eliminate differences between incoming and outgoing traffic and noticed in Wireshark that these settings differ.
RTP is not generally large enough to trigger fragmentation, but you need to be careful how you block ping. You must not block all ICMP otherwise TCP is likely to break