This discussion reveals that Wireshark may not capture every packet on a network. In that case, the reason pertains to TCP data.
I am specifically interested in seeing (extremely bulky) GVSP data. As I understand it, this is based on UDP. I would have thought that even if Wireshark had no filter available for GVSP data, it would at least offer me the UDP data. But I don't see any data at all, despite being absolutely it is transmitted. Why not?
In my situation, I have a PLC triggering a camera regularly, which duly sends its images via GVSP to a host on an isolated network. Also, the PLC sends a UDP packet per trigger event down another isolated network to the same host. On that host, I run Wireshark, I capture on both channels simultaneously, and I see (1) visual evidence of the camera images arriving, (2) Wireshark evidence of the regular UDP packets, and (3) GVCP data from the camera. But the GVSP data is missing. What do I need to do to see this data?