[j-nsp] Setting CoS bits on ingress frames

[Dave Bell]

On 30 July 2015 at 13:07, Victor Sudakov <vas at mpeks.tomsk.su> wrote:
> Dave Bell wrote:
>> When frames enter the switch, the switch will need to classify them
>> and place them into a queue. By default everything goes into queue 0,
>> regardless of what other switches have done.
>
> I am afraid you are mistaken. If a frame enters a switch via a trunk
> port and the frame already has a non-zero COS value, this COS value is
> forwarded *intact* out the egress interface.
>
> I have experimental proof of this. In my lab, Sw1 (Cisco) classifies
> frames and their COS value set by Sw1 is visible at HostC.

When a frame enters port it is classified and placed into a forwarding
class. There are defaults for some traffic types, but for .1p on the
EX, everything goes into the forwarding class that is associated with
queue 0.

On egress, if there is a rewrite rule on the forwarding class on the
egress interface, then all traffic gets set regardless if there is
already markings on the packet.

If there is no rewrite rule on the forwarding class, then the marking
remains unmolested.

The solution to this is to make sure that all your traffic enters the
correct forwarding class on ingress. This means when it egresses the
switch, it will have the intended markings.

Have you tried the configuration I have suggested? Have you looked at
port counters for your interfaces to see what is happening to the
traffic?

Dave