linux-kernel - Re: [RFC 2/2] xen-netback: disable multicast and use a random hw MAC address

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Message-ID: <20140212121946.GA31937@zion.uk.xensource.com>
Date:	Wed, 12 Feb 2014 12:19:46 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>
CC:	Ian Campbell <Ian.Campbell@...rix.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	<xen-devel@...ts.xenproject.org>,
	Paul Durrant <Paul.Durrant@...rix.com>,
	Wei Liu <wei.liu2@...rix.com>, <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 2/2] xen-netback: disable multicast and use a random hw MAC
 address

On Tue, Feb 11, 2014 at 01:53:26PM -0800, Luis R. Rodriguez wrote:
> Cc'ing kvm folks as they may have a shared interest on the shared
> physical case with the bridge (non NAT).
> 
> On Tue, Feb 11, 2014 at 12:43 AM, Ian Campbell <Ian.Campbell@...rix.com> wrote:
> > On Mon, 2014-02-10 at 14:29 -0800, Luis R. Rodriguez wrote:
> >> From: "Luis R. Rodriguez" <mcgrof@...e.com>
> >>
> >> Although the xen-netback interfaces do not participate in the
> >> link as a typical Ethernet device interfaces for them are
> >> still required under the current archtitecture. IPv6 addresses
> >> do not need to be created or assigned on the xen-netback interfaces
> >> however, even if the frontend devices do need them, so clear the
> >> multicast flag to ensure the net core does not initiate IPv6
> >> Stateless Address Autoconfiguration.
> >
> > How does disabling SAA flow from the absence of multicast?
> 
> See patch 1 in this series [0], but I explain the issue I see with
> this on the cover letter [1]. In summary the RFCs on IPv6 make it
> clear you need multicast for Stateless address autoconfiguration
> (SLAAC is the preferred acronym) and DAD, however the net core has not
> made this a requirement, and hence the patch. The caveat which I
> address on the cover letter needs to be seriously considered though.
> 
> [0] http://marc.info/?l=linux-netdev&m=139207142110535&w=2
> [1] http://marc.info/?l=linux-netdev&m=139207142110536&w=2
> 
> > Surely these should be controlled logically independently even if there is some
> > notional linkage.
> 
> When a node hops on a network it will query its network by sending a
> router solicitation multicast request for its configuration
> parameters, the router can respond with router advertisements to
> disable SLAAC.
> 
> Apart from that we have no other means to disable SLAAC neatly, and as
> I gather that would be counter to the IPv6 RFCs anyway, and that makes
> sense.
> 
> > Can SAA not be disabled directly?
> 
> Nope. The ipv6 core assumes all device want ipv6 and this is done upon
> netdev registration, and as I noted on my patch 1 description --
> although ipv6 supports a module parameter to disable autoconfiguration
> RFC4682 Section 5.4 makes it clear that DAD *MUST* be performed on all

FWIW: RFC4862 :-)

You had the same typo in patch 1.

Wei.
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