Q-in-Q packet classification

For my knowledge it's only possible to use the P/Q classifier for the first/outer tag of a double tagged packet. Please keep in mind that only cable modems with P/Q Classifier support can do this. In other words cable modems which have BSoD capabilities. The most cable modems don't.

Here two CMTS output for checking if the cable modem have the filtering support (both haven't support):

Casa:

CASA-CMTS#scm xxxx.xxxx.xxxx verbose | include "Optional Filtering Support"
Optional Filtering Support :{802.1P=N, 802.1Q=N}

Cisco:

CISCO-CMTS#show cable modem xxxx.xxxx.xxxx verbose | include Optional Filtering Support
Optional Filtering Support : {802.1P=N, 802.1Q=N, DUT=N}