Re: [Bridge] Setting the interfaces in promiscuous mode

[Stephen Hemminger <shemminger@osdl.org>]

On Thu, 16 Sep 2004 16:43:40 -0400
Lionel Litty <llitty@gmail.com> wrote:

> > promiscuous mode is tracked in the kernel with a counter, the kernel
> > won't change the actual hardware until the counter goes to zero. This is
> > why running something like tcpdump which changes interface to promiscuous mode
> > will have no effect on the bridge.  How did you
> > force the interface out of non-promiscious mode?  You may not changed anything.
> > 
> 
> I simply did "ifconfig eth0 -promisc" and "ifconfig tap0 -promisc".
> "ifconfig" then no longer indicates that the interfaces are in
> promiscuous mode. Are you saying that the output of ifconfig is not
> reliable and that the interfaces may in fact still be in promiscuous
> mode? This would make sense, but then how come the performance seems
> to be affected by the change?

Because when the stack thinks it is in promiscious mode then all the packets
have to be processed.


> > Also promiscuous on tap means nothing really since there is no hardware
> > filtering.
> 
> OK. I thought there might have been some software simulation of the
> promiscuous mode.
> 
> Thanks, Lionel.