linux-kernel - RE: [Bridge] [PATCH] macvlan: add tap device backend

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Date:	Fri, 7 Aug 2009 19:44:05 +0000
From:	"Fischer, Anna" <anna.fischer@...com>
To:	Stephen Hemminger <shemminger@...tta.com>,
	"Paul Congdon (UC Davis)" <ptcongdon@...avis.edu>
CC:	"drobbins@...too.org" <drobbins@...too.org>,
	"'Paul Congdon (UC Davis)'" <ptcongdon@...avis.edu>,
	'Arnd Bergmann' <arnd@...db.de>,
	"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
	"mst@...hat.com" <mst@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"bridge@...ts.linux-foundation.org" 
	<bridge@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ogerlitz@...taire.com" <ogerlitz@...taire.com>,
	"evb@...oogroups.com" <evb@...oogroups.com>,
	"davem@...emloft.net" <davem@...emloft.net>
Subject: RE: [Bridge] [PATCH] macvlan: add tap device backend

> Subject: Re: [Bridge] [PATCH] macvlan: add tap device backend
> 
> On Fri, 7 Aug 2009 12:10:07 -0700
> "Paul Congdon \(UC Davis\)" <ptcongdon@...avis.edu> wrote:
> 
> > Responding to Daniel's questions...
> >
> > > I have some general questions about the intended use and benefits
> of
> > > VEPA, from an IT perspective:
> > >
> > > In which virtual machine setups and technologies do you forsee this
> > > interface being used?
> >
> > The benefit of VEPA is the coordination and unification with the
> external network switch.  So, in environments where you are
> needing/wanting your feature rich, wire speed, external network device
> (firewall/switch/IPS/content-filter) to provide consistent policy
> enforcement, and you want your VMs traffic to be subject to that
> enforcement, you will want their traffic directed externally.  Perhaps
> you have some VMs that are on a DMZ or clustering an application or
> implementing a multi-tier application where you would normally place a
> firewall in-between the tiers.
> 
> I do have to raise the point that Linux is perfectly capable of keeping
> up without
> the need of an external switch.  Whether you want policy external or
> internal is
> a architecture decision that should not be driven by mis-information
> about performance.

VEPA is not only about enabling faster packet processing (like firewall/switch/IPS/content-filter etc) by doing this on the external switch.

Due to rather low performance of software-based I/O virtualization approaches a lot of effort has recently been going into hardware-based implementations of virtual network interfaces like SRIOV NICs provide. Without VEPA, such a NIC would have to implement sophisticated virtual switching capabilities. VEPA however is very simple and therefore perfectly suited for a hardware-based implementation. So in the future, it will give you direct I/O like performance and all the capabilities your adjacent switch provides.

Anna
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