[c-nsp] IEEE 802.1P QoS Issue........

[Peter Rathlev]

On Mon, 2015-11-02 at 16:29 +0100, Lukas Tribus wrote:
> > , so you would have to mark  on the physical interface,
> > not the subinterface.
> 
> Not so true. Just because you are on a subinterface, doesn't mean
> you can't set cos values.

Interesting. I was genuinely unaware of that, since I have never had the
need and never tried. I would probably advise against actually doing
that since I think some people would find it unintuitive at 3 in the
morning.

> Yes, the COS field isn't theoretically "visible" if you strip the
> dot1q header from the packet on the wire, however that
> doesn't mean the information can't propagate through the
> stack anyway.
> 
> "qos-groups" are available on a lot of platforms, which is
> an internal/local QoS parameter that you can't see on the wire,
> yet you still can set it on ingress and match on egress.
> Because it propagates through the stack/fabric, just as COS
> does.

I'm not intimately familiar with QoS groups, but I'm unsure how they
would help. Or how it is related. Yes, the QoS group tag is internal and
not present on the wire, like "pak_priority". But CoS is not, it
actually exists on the wire, though it might also have an internal
representation.

Being able to set CoS bits anywhere in the processing path (and not via
setting something else and using a map, as I suggested) means the
platform has to actually preserve the p-bits even if it otherwise
discards the Q-tag. It's not a lot of bits of course, so maybe most
platforms do so. But for many switch-based platforms, which I must admit
is what I primarily work with, CoS only exists on the wire. The Cat3k
switches for example (unless I am mistaken and probably not that
platform OP uses of course) have no internal representation of CoS and
can only set it via maps.

That's why I tried to have OP actually reveal the platform. :-)

> Of course, certain platforms may be unable to set COS in
> this situation, but thats a specific limitation then.

It might very well be a ubiquitous feature that only a few platforms
happen to not implement. If that is the case then I have misrepresented
the problem and apologise for that.

I'm not sure how any of this actually helps OP though...

-- 
Peter