Date:	Mon, 30 Sep 2013 20:46:59 +0900
From:	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:	vyasevic@...hat.com
Cc:	Toshiaki Makita <toshiaki.makita1@...il.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	Fernando Luis Vazquez Cao <fernando_b1@....ntt.co.jp>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH net 0/4] bridge: Fix problems around the PVID

On Fri, 2013-09-27 at 14:10 -0400, Vlad Yasevich wrote:
> On 09/27/2013 01:11 PM, Toshiaki Makita wrote:
> > On Thu, 2013-09-26 at 10:22 -0400, Vlad Yasevich wrote:
> >> On 09/26/2013 06:38 AM, Toshiaki Makita wrote:
> >>> On Tue, 2013-09-24 at 13:55 -0400, Vlad Yasevich wrote:
> >>>> On 09/24/2013 01:30 PM, Toshiaki Makita wrote:
> >>>>> On Tue, 2013-09-24 at 09:35 -0400, Vlad Yasevich wrote:
> >>>>>> On 09/24/2013 07:45 AM, Toshiaki Makita wrote:
> >>>>>>> On Mon, 2013-09-23 at 10:41 -0400, Vlad Yasevich wrote:
> >>>>>>>> On 09/17/2013 04:12 AM, Toshiaki Makita wrote:
> >>>>>>>>> On Mon, 2013-09-16 at 13:49 -0400, Vlad Yasevich wrote:
> >>>>>>>>>> On 09/13/2013 08:06 AM, Toshiaki Makita wrote:
> >>>>>>>>>>> On Thu, 2013-09-12 at 16:00 -0400, David Miller wrote:
> >>>>>>>>>>>> From: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
> >>>>>>>>>>>> Date: Tue, 10 Sep 2013 19:27:54 +0900
> >>>>>>>>>>>>
> >>>>>>>>>>>>> There seem to be some undesirable behaviors related with PVID.
> >>>>>>>>>>>>> 1. It has no effect assigning PVID to a port. PVID cannot be applied
> >>>>>>>>>>>>> to any frame regardless of whether we set it or not.
> >>>>>>>>>>>>> 2. FDB entries learned via frames applied PVID are registered with
> >>>>>>>>>>>>> VID 0 rather than VID value of PVID.
> >>>>>>>>>>>>> 3. We can set 0 or 4095 as a PVID that are not allowed in IEEE 802.1Q.
> >>>>>>>>>>>>> This leads interoperational problems such as sending frames with VID
> >>>>>>>>>>>>> 4095, which is not allowed in IEEE 802.1Q, and treating frames with VID
> >>>>>>>>>>>>> 0 as they belong to VLAN 0, which is expected to be handled as they have
> >>>>>>>>>>>>> no VID according to IEEE 802.1Q.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> Note: 2nd and 3rd problems are potential and not exposed unless 1st problem
> >>>>>>>>>>>>> is fixed, because we cannot activate PVID due to it.
> >>>>>>>>>>>>
> >>>>>>>>>>>> Please work out the issues in patch #2 with Vlad and resubmit this
> >>>>>>>>>>>> series.
> >>>>>>>>>>>>
> >>>>>>>>>>>> Thank you.
> >>>>>>>>>>>
> >>>>>>>>>>> I'm hovering between whether we should fix the issue by changing vlan 0
> >>>>>>>>>>> interface behavior in 8021q module or enabling a bridge port to sending
> >>>>>>>>>>> priority-tagged frames, or another better way.
> >>>>>>>>>>>
> >>>>>>>>>>> If you could comment it, I'd appreciate it :)
> >>>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>> BTW, I think what is discussed in patch #2 is another problem about
> >>>>>>>>>>> handling priority-tags, and it exists without this patch set applied.
> >>>>>>>>>>> It looks like that we should prepare another patch set than this to fix
> >>>>>>>>>>> that problem.
> >>>>>>>>>>>
> >>>>>>>>>>> Should I include patches that fix the priority-tags problem in this
> >>>>>>>>>>> patch set and resubmit them all together?
> >>>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>> I am thinking that we might need to do it in bridge and it looks like
> >>>>>>>>>> the simplest way to do it is to have default priority regeneration table
> >>>>>>>>>> (table 6-5 from 802.1Q doc).
> >>>>>>>>>>
> >>>>>>>>>> That way I think we would conform to the spec.
> >>>>>>>>>>
> >>>>>>>>>> -vlad
> >>>>>>>>>
> >>>>>>>>> Unfortunately I don't think the default priority regeneration table
> >>>>>>>>> resolves the problem because IEEE 802.1Q says that a VLAN-aware bridge
> >>>>>>>>> can transmit untagged or VLAN-tagged frames only (the end of section 7.5
> >>>>>>>>> and 8.1.7).
> >>>>>>>>>
> >>>>>>>>> No mechanism to send priority-tagged frames is found as far as I can see
> >>>>>>>>> the standard. I think the regenerated priority is used for outgoing PCP
> >>>>>>>>> field only if egress policy is not untagged (i.e. transmitting as
> >>>>>>>>> VLAN-tagged), and unused if untagged (Section 6.9.2 3rd/4th Paragraph).
> >>>>>>>>>
> >>>>>>>>> If we want to transmit priority-tagged frames from a bridge port, I
> >>>>>>>>> think we need to implement a new (optional) feature that is above the
> >>>>>>>>> standard, as I stated previously.
> >>>>>>>>>
> >>>>>>>>> How do you feel about adding a per-port policy that enables a bridge to
> >>>>>>>>> send priority-tagged frames instead of untagged frames when egress
> >>>>>>>>> policy for the port is untagged?
> >>>>>>>>> With this change, we can transmit frames for a given vlan as either all
> >>>>>>>>> untagged, all priority-tagged or all VLAN-tagged.
> >>>>>>>>
> >>>>>>>> That would work.  What I am thinking is that we do it by special casing
> >>>>>>>> the vid 0 egress policy specification.  Let it be untagged by default
> >>>>>>>> and if it is tagged, then we preserve the priority field and forward
> >>>>>>>> it on.
> >>>>>>>>
> >>>>>>>> This keeps the API stable and doesn't require user/admin from knowing
> >>>>>>>> exactly what happens.  Default operation conforms to the spec and allows
> >>>>>>>> simple change to make it backward-compatible.
> >>>>>>>>
> >>>>>>>> What do you think.  I've done a simple prototype of this an it seems to
> >>>>>>>> work with the VMs I am testing with.
> >>>>>>>
> >>>>>>> Are you saying that
> >>>>>>> - by default, set the 0th bit of untagged_bitmap; and
> >>>>>>> - if we unset the 0th bit and set the "vid"th bit, we transmit frames
> >>>>>>> classified as belonging to VLAN "vid" as priority-tagged?
> >>>>>>>
> >>>>>>> If so, though it's attractive to keep current API, I'm worried about if
> >>>>>>> it could be a bit confusing and not intuitive for kernel/iproute2
> >>>>>>> developers that VID 0 has a special meaning only in the egress policy.
> >>>>>>> Wouldn't it be better to adding a new member to struct net_port_vlans
> >>>>>>> instead of using VID 0 of untagged_bitmap?
> >>>>>>>
> >>>>>>> Or are you saying that we use a new flag in struct net_port_vlans but
> >>>>>>> use the BRIDGE_VLAN_INFO_UNTAGGED bit with VID 0 in netlink to set the
> >>>>>>> flag?
> >>>>>>>
> >>>>>>> Even in that case, I'm afraid that it might be confusing for developers
> >>>>>>> for the same reason. We are going to prohibit to specify VID with 0 (and
> >>>>>>> 4095) in adding/deleting a FDB entry or a vlan filtering entry, but it
> >>>>>>> would allow us to use VID 0 only when a vlan filtering entry is
> >>>>>>> configured.
> >>>>>>> I am thinking a new nlattr is a straightforward approach to configure
> >>>>>>> it.
> >>>>>>
> >>>>>> By making this an explicit attribute it makes vid 0 a special case for
> >>>>>> any automatic tool that would provision such filtering.  Seeing vid 0
> >>>>>> would mean that these tools would have to know that this would have to
> >>>>>> be translated to a different attribute instead of setting the policy
> >>>>>> values.
> >>>>>
> >>>>> Yes, I agree with you that we can do it by the way you explained.
> >>>>> What I don't understand is the advantage of using vid 0 over another way
> >>>>> such as adding a new nlattr.
> >>>>> I think we can indicate transmitting priority-tags explicitly by such a
> >>>>> nlattr. Using vid 0 seems to be easier to implement than a new nlattr,
> >>>>> but, for me, it looks less intuitive and more difficult to maintain
> >>>>> because we have to care about vid 0 instead of simply ignoring it.
> >>>>>
> >>>>
> >>>> The point I am trying to make is that regardless of the approach someone
> >>>> has to know what to do when enabling priority tagged frames.  You
> >>>> proposal would require the administrator or config tool to have that
> >>>> knowledge.  Example is:
> >>>> 	Admin does: bridge vlan set priority on dev eth0
> >>>>            Automated app:
> >>>> 		if (vid == 0)
> >>>> 			/* Turn on priority tagged frame support */
> >>>>
> >>>> My proposal would require the bridge filtering implementation to have it.
> >>>> 	user tool: bridge vlan add vid 0 tagged
> >>>> 	Automated app:  No special case.
> >>>>
> >>>> IMO its better to have 1 piece code handling the special case then
> >>>> putting it multiple places.
> >>>
> >>> Thank you for the detailed explanation.
> >>> Now I understand your intention.
> >>>
> >>> I have one question about your proposal.
> >>> I guess the way to enable priority-tagged is something like
> >>> 	bridge vlan add vid 10 dev eth0
> >>> 	bridge vlan add vid 10 dev vnet0 pvid untagged
> >>> 	bridge vlan add vid 0 dev vnet0 tagged
> >>> where vnet0 has sub interface vnet0.0.
> >>>
> >>> Here the admin have to know the egress policy is applied to a frame
> >>> twice in a certain order when it is transmitted from the port vnet0
> >>> attached, that is, first, a frame with vid 10 get untagged, and then, an
> >>> untagged frame get priority-tagged.
> >>>
> >>> This behavior looks difficult to know without previous knowledge.
> >>> Any good idea to avoid such a need for the admin's additional knowledge?
> >>
> >> To me, the fact that there is vnet0.0 (or typically, there is eth0.0 in
> >> the guest or on the remote host) already tells the admin vlan 0 has to
> >> be tagged.  The fact that we codify this in the policy makes it explicit.
> >
> > My worry is that the admin might not be able to guess how to use bridge
> > commands to enable priority-tag without any additional hint in "man
> > bridge", "bridge vlan help", etc.
> > I actually couldn't hit upon such a usage before seeing example commands
> > you gave, because I had never think the egress policy could be applied
> > twice.
> >
> >>
> >> However, I can see strong argument to be made for an addition egress
> >> policy attribute that could be for instance:
> >>
> >> 	bridge vlan add vid 10 dev eth0 pvid
> >> 	bridge vlan add vid 10 dev vnet0 pvid untagged prio_tag
> >>
> >> But this has the same connotations as wrt to egress policy.  The 2
> >> policies are applied:
> >>    (1) untag the frame.
> >>    (2) add priority_tag.
> >>
> >> (2) only happens if initial fame received on eth0 was priority tagged.
> >
> > If we do so, we will not be able to communicate using vlan 0 interface
> > under a certain circumstance.
> > Eth0 can be receive mixed untagged and priority-tagged frames according
> > to the network element it is connected to: for example, Open vSwitch can
> > send such two kinds of frames from the same port even if original
> > incoming frames belong to the same vlan.
> 
> Which priority would you assign to the frame that was received untagged?

Untagged frame's priority is by default 0, so I think 0 is likely.

802.1Q 6.9.1 i)
  The received priority value and the drop_eligible parameter value are
  the values in the M_UNITDATA.indication.

M_UNITDATA is passed from ISS.

802.1Q 6.7.1
  The priority parameter provided in a data indication primitive shall
  take the value of the Default User Priority parameter for the Port
  through which the MAC frame was received. The default value of this
  parameter is 0, it may be set by management in which case the 
  capability to set it to any of the values 0 through 7 shall be
  provided.

> 
> > In this situation, we can only receive frames that is priority-tagged
> > when received on eth0.
> 
> Not sure I understand.  Let's look at this config:
> 	bridge vlan add vid 10 dev eth0 pvid
> 	bridge vlan add vid 10 dev vnet0 pvid untagged prio_tag
> 
> Here, eth0 is allowed to receive vid 10 tagged, untagged, and 
> prio_tagged (if we look at the patch 2 from this set).
> Now, frame is forwarded to vnet0.
> 	1) if the frame had vid 10 in the tag or was untagged,
> 	   it should probably be sent untagged.
> 	2) if the frame had a priority tag, it should probably
> 	   be sent as such.
> 
> Now, I think a case could be made that if the frame had any priority
> markings in the vlan header, we should try to preserve those markings
> if prio_tag is turned on.  We can assume value of 0 means not set.

If we don't insert prio_tag when PCP is 0, we might receive mixed
priority-tagged and untagged frames on eth0.
Even if we are sending frames from eth0.0 with some priority other than
0, we could receive frames with priority 0 or untagged on the other side
of the bridge.
For example, if we receive untagged arp reply on the bridge port, we
migit not be able to communicate with such an end station, because
untagged reply will not be passed to eth0.0.

> 
> > IMO, if prio_tag is configured, the bridge should send any untagged
> > frame as priority-tagged regardless of whatever it is on eth0.
> 
> Which priority would you use, 0?  You are not guaranteed to properly
> deliver the traffic then for a configuration such as:
>      VM: eth0: 10.0.0.1/24
>          eth0.0: 10.0.1.1/24

I'd like to use priority 0 for untagged frames.

I am assuming that one of our goals is at least that eth0.0 comes to be
able to communicate with another end station. It seems to be hard to use
both eth0 and eth0.0 simultaneously.

Thanks,

Toshiaki Makita

> 
> -vlad
> 
> >
> >>
> >> I think I am ok with either approach.  Explicit vid 0 policy is easier
> >> for automatic provisioning.   The flag based one is easier for admin/
> >> manual provisioning.
> >
> > Supposing we have to add something to help or man in any case, I think
> > flag based is better.
> > The format below seems to suitable for a per-port policy.
> > 	bridge vlan set prio_tag on dev vnet0
> >
> > Thanks,
> >
> > Toshiaki Makita
> >
> >>
> >> -vlad.
> >>
> >> -vlad
> >>
> >>
> >>
> >>
> >>>
> >>>>
> >>>> Thanks
> >>>> -vlad
> >>>>
> >>>>> Thanks,
> >>>>>
> >>>>> Toshiaki Makita
> >>>>>
> >>>>>>
> >>>>>> How it is implemented internally in the kernel isn't as big of an issue.
> >>>>>> We can do it as a separate flag or as part of existing policy.
> >>>>>>
> >>>>>> -vlad
> >>>>>>
> >>>>>>>
> >>>>>>> Thanks,
> >>>>>>>
> >>>>>>> Toshiaki Makita
> >>>>>>>
> >>>>>>>>
> >>>>>>>> -vlad
> >>>>>>>>
> >>>>>>>>>
> >>>>>>>>> Thanks,
> >>>>>>>>>
> >>>>>>>>> Toshiaki Makita
> >>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>> Thanks,
> >>>>>>>>>>>
> >>>>>>>>>>> Toshiaki Makita
> >>>>>>>>>>>
> >>>>>>>>>>>>
> >>>>>>>>>>>> --
> >>>>>>>>>>>> To unsubscribe from this list: send the line "unsubscribe netdev" in
> >>>>>>>>>>>> the body of a message to majordomo@...r.kernel.org
> >>>>>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >>>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> --
> >>>>>>>>> To unsubscribe from this list: send the line "unsubscribe netdev" in
> >>>>>>>>> the body of a message to majordomo@...r.kernel.org
> >>>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >>>>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>
> >>>>>
> >>>>>
> >>>
> >>>
> >>
> >
> >


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