DNS recursive resolver - no handling of private-use RRTypes?

[EskoDijk]

Describe the bug A clear and concise description of what the bug is.

In testing, it was found that an OTBR successfully sends a query to the upstream DNS server for a well-known RRType like "A" or "AAAA", but that the OTBR does not send a query upstream for a more obscure RRType like the private-use types ( >= 0xff00 ). See registry.

To Reproduce Information to reproduce the behavior, including:

This result was provided by GRL - details on the OTBR reference build can be added.
(I didn't have time yet to reproduce this with my own OTBR reference build; I vaguely remember that it did work earlier but not sure about that. That will come in 2025!)

Maybe someone already knows if this is supported, and why / why not.

1. Git commit id
2. IEEE 802.15.4 hardware platform
3. Build steps
4. Network topology

Cert test case 11.5 in test plan R9, using RRType 0xff05.

Expected behavior A clear and concise description of what you expected to happen.

OTBR forwards the valid DNS query to the upstream DNS server.

Console/log output If applicable, add console/log output to help explain your problem.

(can be provided if needed)

One problem in the OTBR DUT used is that it generates no useful log information, for unknown reasons (no OT core logs - though it has some TREL and PySpinel related logging). I could try to rerun with my own OTBR.

Additional context Add any other context about the problem here.