Unable to attach physical interfaces to netmap vale switch

[h bagade]

Hi all,

I've tried to attach my physical interfaces to vale using
vale-ctl -a em1
and encountered the error:
bdg_ctl [74] Unable to attach em1 to the bridge

But I can bridge em0 and em1 using netmap bridge!
I think if there is problem with registering the interface so I should not
be able to bridge them but I can. What's missing here?