netdev - Re: [PATCH 3/3] ipvlan: set dev_id for l2 ports to generate unique IPv6 addresses

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Message-Id: <1432210147.2501736.274695753.11571414@webmail.messagingengine.com>
Date:	Thu, 21 May 2015 14:09:07 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	Mahesh Bandewar <maheshb@...gle.com>
Cc:	"linux-netdev" <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Jiri Benc <jbenc@...hat.com>
Subject: Re: [PATCH 3/3] ipvlan: set dev_id for l2 ports to generate unique IPv6
 addresses

On Thu, May 21, 2015, at 13:38, Konstantin Khlebnikov wrote:
> On 20.05.2015 02:59, Mahesh Bandewar wrote:
> > On Thu, May 14, 2015 at 6:56 AM, Konstantin Khlebnikov
> > <khlebnikov@...dex-team.ru> wrote:
> >> All ipvlan ports use one MAC address, this way ipv6 RA tries to assign
> >> one ipv6 address to all of them. This patch assigns unique dev_id to each
> >> ipvlan port. This field is used instead of common FF-FE in Modified EUI-64.
> >>
> >> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
> >> ---
> >>   Documentation/networking/ipvlan.txt |   12 +++++++++++-
> >>   drivers/net/ipvlan/ipvlan.h         |    1 +
> >>   drivers/net/ipvlan/ipvlan_main.c    |   20 ++++++++++++++++++++
> >>   3 files changed, 32 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/Documentation/networking/ipvlan.txt b/Documentation/networking/ipvlan.txt
> >> index cf996394e466..cb0b777bce58 100644
> >> --- a/Documentation/networking/ipvlan.txt
> >> +++ b/Documentation/networking/ipvlan.txt
> >> @@ -24,7 +24,7 @@ using IProute2/ip utility.
> >>
> >>          ip link add link <master-dev> <slave-dev> type ipvlan mode { l2 | L3 }
> >>
> >> -       e.g. ip link add link ipvl0 eth0 type ipvlan mode l2
> >> +       e.g. ip link add link eth0 ipvl0 type ipvlan mode l2
> >>
> >>
> >>   4. Operating modes:
> >> @@ -41,6 +41,15 @@ slave device and packets are switched and queued to the master device to send
> >>   out. In this mode the slaves will RX/TX multicast and broadcast (if applicable)
> >>   as well.
> >>
> >> +       In L2 mode slave devices receive Router Advertisements from the network
> >> +and perform autoconfiguration as well as master device. Each port has unique
> >> +16-bit device id which is used for filling octets 4-5 of Modified EUI-64.
> >> +That gives 65533 addresses (FF-FE used by master, FF-FF/00-00 reserved/not used).
> >> +
> > This is nice, thanks for fixing this! However how is "unique" id
> > guaranteed? Especially when multiple virtual drivers are stacked? Not
> > necessarily all of them may use the dev_id, but to avoid any possible
> > collision, shouldn't the device hierarchy (especially lower_dev) be
> > traversed before settling on the initial value?
> 
> Well, uniqueness isn't guaranteed but that should work in most cases.
> ipv6 anyway checks for duplicate addresses after configuration.
> 
> As I see creation of ipvlan on ipvlan just creates slave at original
> master device, so this will work as expected. And ipvlan cannot share 
> physical device with bonding/bridge/macvlan, so I don't see how to
> stack more than one layer of ipvlans accidentally.

I hope that stable ipv6 privacy addresses will be used in future and old
eui-48 based LL addresses will just disappear. That said, I would be
even fine with a RNG generated dev_id, because we cannot really ensure
uniqueness.

Stable privacy addresses even use DAD retry counter to regenerate a new
LL address in case the address becomes IFA_F_DADFAILED.

Bye,
Hannes
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