pfSense

On an upgrade to the 2.5 dev snapshot, I had multiple messages about this, warning me the em0.90 didnt support altq, on the first boot.
As I was digging through my config to try and work out where it was coming from, these suddenly stopped.
At no point did I get any warnings about the other 15 or so vlans on that parent nic.

Not much help for debugging I'm afraid!

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=94182:

vlan driver does not directly support altq
but as packets (mbufs) are passed to the underlying interface, a queue
can be defined for the underlying interface, and any packets directed
to the queue will be processed at the interface level.
An example:

altq on igb0 cbq queue { def aq }
queue def bandwidth 90% cbq (default borrow)
queue aq bandwidth 10Mb cbq

pass in on igb0.10 proto udp all queue aq keep state

That doesn't work for some cases like lagg and ix, which do not support ALTQ natively, and can't have it enabled for various reasons. Using VLANs to enact ALTQ shaping is a workaround for those interfaces (and others)