Some GRE traffic is not visible on the "parent" interface

[Bernie]

Hi,

I've an intresting problem with a GRE tunnel, maybe you have some advice. I use the tunnel inbetween opnsense and another VM host. I'm running Voip-traffic within that tunnel. Most of the time everything runs fine but sometimes RTP traffic that is going outbound on the GRE interface from the opnsense host does not reach the other host.
When running packet capture on the OPNsense host I see all those RTP packets within the capture of the GRE-interface. However those packets are completely missing on the parent interface (vtnet2 in my case). Other packets (i.e. SIP control packets) are still there also during the running conversation, only the whole RTP stream is missing. RTP inbound and control traffic is working fine. Do you have any ideas what could cause this?

Currently I'm thinking of trying L2TP as an alternative, but I'd really like to know what is wrong here.
I'm running the current opnsense stable realease (20.7)
-
Bernie

[Bernie]

Hi,
I changed my configuration to use an GIF (ipipv4)-Tunnel. This solution does not have the problem with missing packages (and for me the advantage of saving some more Header bytes). Maybe there's even a problem with the GRE stack in the underlying BSD system?
-
Bernie