Network interface RUNNING and UP flags

[Coleman Kane]

Hi, I have been having some trouble working with getting tapN network
interfaces into the 'RUNNING' state. I have been trying to figure out
how to set the RUNNING flag on an interface, which is needed before
the kernel will actually begin sending packets from said network
interface. So far, the only way I have been able to figure out how to
do this is to assign an IPv4 address to the interface, I am guessing
that an un-addressed network interface is supposed to remain not
RUNNING even if it is UP by design. The problem is that only an IPv4
address assignment will bring it up and running. If I attempt to
assign an IPv6 address to the interface, it will go UP, but not
RUNNING. I have determined that I can assign an IPv4 address (such as
10.0.0.1) to it, and then subsequently remove it (via -alias) and this
will leave the interface in the running state.

My questions are:

1) Why doesn't assigning an IPv6 address produce the same side effects
and
2) Is there a way to set this interface flag without assigning an IPv4
address (or any address for that matter) first?

Mainly for number two, I would like to be able to run interfaces
bridged together without having to also give all of them addresses.

--
thanks,
coleman kane