Xen users - Feb 2009 - Xen''s interface in promiscuous mode

Hello all,
Playing with Xen on GNU/Debian Lenny, I just discovered that all my 
virtual network cards are in promiscuous mode by default.
Changing that manually does not seems to change anything (that is, 
everything still works great).

Is there any reason to have virtual network cards in promiscuous mode ?
And where can I change this default behaviour ?

Thanks,
JB

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> 
> Hello all,
> Playing with Xen on GNU/Debian Lenny, I just discovered that all my
> virtual network cards are in promiscuous mode by default.
> Changing that manually does not seems to change anything (that is,
> everything still works great).
> 
> Is there any reason to have virtual network cards in promiscuous mode
?
> And where can I change this default behaviour ?
> 
The physical network adapters in Dom0 will be in promiscuous mode if
they are joined to a bridge.

The virtual network adapters in DomU are in promiscuous modem because
(as of the version of Xen in Lenny) they don''t support multicast, and
so
the only way they can receive multicast packets is to be in promiscuous
mode.

As of 3.3.0 or thereabouts, there is a way for the frontend to tell the
backend which multicast packets it is interested in, so the behaviour
may be different there.

James

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El Lunes 23 Febrero 2009, James Harper escribió:
> > Hello all,
> > Playing with Xen on GNU/Debian Lenny, I just discovered that all my
> > virtual network cards are in promiscuous mode by default.
> > Changing that manually does not seems to change anything (that is,
> > everything still works great).
> >
> > Is there any reason to have virtual network cards in promiscuous mode
>
> ?
>
> > And where can I change this default behaviour ?
>
> The physical network adapters in Dom0 will be in promiscuous mode if
> they are joined to a bridge.
>
> The virtual network adapters in DomU are in promiscuous modem because
> (as of the version of Xen in Lenny) they don''t support multicast,
and so
> the only way they can receive multicast packets is to be in promiscuous
> mode.
>
> As of 3.3.0 or thereabouts, there is a way for the frontend to tell the
> backend which multicast packets it is interested in, so the behaviour
> may be different there.
Hi James,

Can you elaborate on that, or give a link to read more about it?

TIA and best regards,
-- 
Ricardo J. Barberis 
Senior SysAdmin - I+D 
Dattatec.com :: Soluciones de Web Hosting 

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> 
> El Lunes 23 Febrero 2009, James Harper escribió:
> > > Hello all,
> > > Playing with Xen on GNU/Debian Lenny, I just discovered that all
my
> > > virtual network cards are in promiscuous mode by default.
> > > Changing that manually does not seems to change anything (that
is,
> > > everything still works great).
> > >
> > > Is there any reason to have virtual network cards in promiscuous
mode
> >
> > ?
> >
> > > And where can I change this default behaviour ?
> >
> > The physical network adapters in Dom0 will be in promiscuous mode if
> > they are joined to a bridge.
> >
> > The virtual network adapters in DomU are in promiscuous modem because
> > (as of the version of Xen in Lenny) they don''t support
multicast, and so
> > the only way they can receive multicast packets is to be in
promiscuous
> > mode.
> >
> > As of 3.3.0 or thereabouts, there is a way for the frontend to tell
the
> > backend which multicast packets it is interested in, so the behaviour
> > may be different there.
> 
> Hi James,
> 
> Can you elaborate on that, or give a link to read more about it?
> 
Unless someone has written up some docs, your best bet is to look at the code -
specifically the headers in xen/include/public/io

James

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El Miércoles 25 Febrero 2009, James Harper escribió:
> > El Lunes 23 Febrero 2009, James Harper escribió:
> > > The physical network adapters in Dom0 will be in promiscuous mode
if
> > > they are joined to a bridge.
> > >
> > > The virtual network adapters in DomU are in promiscuous modem
because
> > > (as of the version of Xen in Lenny) they don''t support
multicast, and
> > > so the only way they can receive multicast packets is to be in
> > > promiscuous mode.
> > >
> > > As of 3.3.0 or thereabouts, there is a way for the frontend to
tell the
> > > backend which multicast packets it is interested in, so the
behaviour
> > > may be different there.
> >
> > Hi James,
> >
> > Can you elaborate on that, or give a link to read more about it?
>
> Unless someone has written up some docs, your best bet is to look at the
> code - specifically the headers in xen/include/public/io
>
> James
OK, despite my limited C knowledge I''ll have to digg in :-)

Thank you,
-- 
Ricardo J. Barberis
Senior SysAdmin - I+D
Dattatec.com :: Soluciones de Web Hosting

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