On Wed, Feb 05, 2014 at 05:54:38PM +0900, Simon Horman wrote:
> * Ben has explained to me that there has been a change of direction
> at the ONF with regards to MPLS and VLAN tag ordering. As per
> his changelog for "Always insert MPLS labels after VLAN tags",
> the situation is now as follows:
>
> * OpenFlow 1.1 and 1.2 always inserted MPLS labels after VLAN tags.
> * OpenFlow 1.3 and 1.4 insert MPLS labels before VLAN tags.
> * OpenFlow 1.3.4 and 1.5, both in preparation, recognize that the change
> in 1.3 was an error and revert it.
>
> With this in mind only OF1.4 specifies a requirement for inserting MPLS
> labels before VLAN tags. This appears to be an abbertation at this
> point.
>
> Ben's suggestion as per his patch "Always insert MPLS labels after VLAN
> tags" is that Open vSwtich should only support inserting MPLS labels
> after VLAN tags. I agree with this. And to this end I have
> updated the MPLS code for the kernel datapath (this patch).
I spoke to Jesse briefly about MPLS versus VLANs a few days ago. He
expressed a concern about the larger problem of figuring out how all the
various forms of tags should interact: VLAN, MPLS, PBB, and others that
I can't think of at the moment. It would be more consistent from this
higher point of view if "push" and "pop" actions always acted in a
predictable place.
I agree with that point, but it still stands that I don't know of a
well-defined way for VLAN-inside-MPLS to function. So here is my
proposal for you and Jesse to consider:
- The datapath push_mpls action is well-defined when no VLAN is
present. Great.
- Declare the behavior of the datapath push_mpls action to be
undefined in the presence of a VLAN for now, since we don't
really know what should happen. For now, make the datapaths
reject any flow that does push_mpls in the presence of a VLAN.
Later, we can redefine that case as we please since userspace
should not depend on the previous behavior.
- Modify userspace to pop_vlan, push_mpls, push_vlan if
necessary to avoid the undefined behavior.
Jesse, is that reasonable?
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