Work within the GRE/PPTP/L2TP/IPIP tunnels
DPI doesn't parse the tunnels 1) by default, since the traffic of different operators or clients with a conflicting IPs can be transmitted, but for non-standard connection (before BRAS), tunneling parsing is necessary.
In the Lawful Interception prefilter, tunnel parsing is enabled automatically by the presence of the tap_dev parameter. In other cases, you will need to explicitly enable parsing with the configuration parameter in the /etc/dpi/fastdpi.conf file
check_tunnels=1
enables parsing PPTP/L2TP/GRE/IPIP tunnels.
1)
tagged VLAN/QINQ and MPLS traffic are not considered as tunnel