The operating system Windows cannot handle VLAN tags. Therefore a network driver is needed to enable VLAN handling. In many cases the VLAN tags are filtered by the driver, therefore so that they are not included in a Wireshark trace of a mirror port. This can complicate the analysis of VLAN problems in a network enormously.
With some manfufacturers settings can be changed in the driver software, so that the VLAN tags are not filtered anymore. With other manufacturers changes have to be made in the registry to achieve that. Additional information can be found on the Wireshark website. | 