http://docs.freebsd.org/cgi/getmsg.cgi?fetch=38062+0+current/freebsd-arch
“I think I ran into the related problem. The vlan device calls
IFQ_HANDOFF directly versus the "normal" output bits so you can't
use netgraph etc. I broke up ether_output so that I could
call the stuff that ether_output does so it would go through
netgraph hooks if configured.
Doug A.”
