Date:   Tue, 30 Jan 2018 01:53:23 +0000
From:   "Yuan, Linyu (NSB - CN/Shanghai)" <linyu.yuan@...ia-sbell.com>
To:     "Keller, Jacob E" <jacob.e.keller@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "Duyck, Alexander H" <alexander.h.duyck@...el.com>
Subject: RE: macvlan devices and vlan interaction

https://www.spinics.net/lists/netdev/msg476083.html

I also have a macvlan device question, but get no answer.

But my original thought is in __netif_receive_skb_core() we should check packet destination mac address,
if it match macvlan device, change packet as receive from macvlan device, not lower device, then packet go to upper layer.

But I don't know how to process broadcast mac address. Do macvlan device can receive broadcast packet ?

> -----Original Message-----
> From: netdev-owner@...r.kernel.org [mailto:netdev-owner@...r.kernel.org]
> On Behalf Of Keller, Jacob E
> Sent: Tuesday, January 30, 2018 7:02 AM
> To: netdev@...r.kernel.org
> Cc: Duyck, Alexander H
> Subject: macvlan devices and vlan interaction
> 
> Hi,
> 
> I'm currently investigating how macvlan devices behave in regards to vlan
> support, and found some interesting behavior that I am not sure how best to
> correct, or what the right path forward is.
> 
> If I create a macvlan device:
> 
> ip link add link ens0 name macvlan0 type macvlan:
> 
> and then add a VLAN to it:
> 
> ip link add link macvlan0 name vlan10 type vlan id 10
> 
> This works to pass VLAN 10 traffic over the macvlan device. This seems like
> expected behavior.
> 
> However, if I then also add vlan 10 to the lowerdev:
> 
> ip link add link ens0 name lowervlan10  type vlan id 10
> 
> Then traffic stops flowing to the VLAN on the macvlan device.
> 
> This happens, as far as I can tell, because of how the VLAN traffic is filtered
> first, and then forwarded to the VLAN device, which doesn't know about how
> the macvlan device exists.
> 
> It seems, essentially, that vlan stacked on top of a macvlan shouldn't work.
> Because the vlan code basically expects each vlan to apply to every MAC
> address, and the macvlan device works by putting its MAC address into the
> unicast address list, there's no way for a device driver to know when or how to
> apply the vlan.
> 
> This gets a bit more confusing when we add in the l2 fwd hardware offload.
> 
> Currently, at least for the Intel network parts, this isn't supported, because of a
> bug in which the device drivers don't apply the VLANs to the macvlan
> accelerated addresses. If we fix this, at least for fm10k, the behavior is slightly
> better, because of how the hardware filtering at the MAC address happens
> first, and we direct the traffic to the proper device regardless of VLAN.
> 
> In addition to this peculiarity of VLANs on both the macvlan and lowerdev, is
> that when a macvlan device adds a VLAN, the lowerdev gets an indication to
> add the vlan via its .ndo_vlan_rx_add_vid(), which doesn't distinguish between
> which addresses the VLAN might apply to. It thus simply, depending on
> hardware design, enables the VLAN for all its unicast and multicast addresses.
> Some hardware could theoretically support MAC+VLAN pairs, where it could
> distinguish that a VLAN should only be added for some subset of addresses.
> Other hardware might not be so lucky..
> 
> Unfortunately, this has the weird consequence that if we have the following
> stack of devices:
> 
> vlan10@...vlan0
> macvlan0@...0
> ens0
> 
> Then ens0 will receive VLAN10 traffic on every address. So VLAN 10 traffic
> destined to the MAC of the lowerdev will be received, instead of dropped.
> 
> If we add VLAN 10 to the lowerdev so we have both the above stack and also
> 
> lowervlan10@...0
> ens0 (mac gg:hh:ii:jj:kk)
> 
> then all vlan 10 traffic will be received on the lowerdev VLAN 10, without any
> being forwarded to the VLAN10 attached to the macvlan.
> 
> However, if we add two macvlans, and each add the vlan10, so we have the
> following:
> 
> avlan10@...vlan0
> macvlan0@...0
> ens0
> 
> bvlan10@...vlan1
> macvlan1@...0
> ens0
> 
> In this case, it does appear that traffic is sorted out correctly. It seems that
> only if the lowerdev gets the VLAN does it end up breaking. If I remove bvlan10
> from macvlan1, the traffic associated with vlan10 is still received by macvlan1,
> even though in principle it should no longer be.
> 
> What is the correct behavior here? Should this just be "administrators should
> know better"? I don't think that's a great argument, and either way we're still
> essentially leaking VLANs across the macvlan interfaces, which I don't think is
> ideal.
> 
> I see two possible solutions:
> 
> 1) modify macvlan driver so that it is marked as VLAN_CHALLENGED, and thus
> indicate it cannot handle VLAN traffic on top of it.
>   a. In order to get the VLANs associated, administrator could instead add the
> VLAN first, and then add the macvlan on top. This I think is a better
> configuration.
>   b. that doesn't work in the offload case, unless/until we fix the VLAN
> interface to forward the l2_dfwd_add_station() along with a vid.
>   c. this could appear as loss of functionality, since in some cases these VLAN
> on top of macvlan work today (with the interesting caveats listed above).
> 
> 2) modify how VLANs interact with MAC addresses, so that the lowerdev can
> explicitly be aware of which VLANs are tied to which address groups, in order to
> allow for the explicit configuration of which MAC+VLAN pairs are actually
> allowed.
>   a. this is a much more invasive change to driver interface, and more difficult
> to get right
>   b. possibly other configurations of stacked devices might have a similar
> problem, so we could solve more here? Or create more problems.. I'm not
> really certain.
> 
> 
> I think the correct solution is (1) but I wasn't sure what others thought, and
> whether anyone else has encountered the problems I mention and outline
> above. I cc'd Alex who I discussed with offline when I first heard of and began
> investigating this, in case he has anything further to add.
> 
> Regards,
> Jake

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