[j-nsp] CoS and ingress traffic with DSCP markings

[Dave Bell]

Hi John,

As far as I'm aware, when traffic hits the box, it has to be put into a
forwarding class. If you have not defined any, it will drop into the
default forwarding class. There are commands you can run that will show you
what forwarding classes are attached to your interfaces - I can't remember
them off the top of my head though!

If you do have rewrite rules on egress, then you will likely mark it to DF
as you were seeing. It sounds like you have hit the nail on the head.

Dave


On 22 January 2014 16:20, John Neiberger <jneiberger at gmail.com> wrote:

> I ran into an issue yesterday that confused me, which seems to be a
> weekly occurrence lately regarding Juniper CoS.. We had an interface
> that was receiving traffic marked as EF. The interface only had the
> default CoS configuration. For some reason, the traffic was arriving
> at the destination marked as CS0. After I applied the CoS group to the
> interface, which included classifiers, the packets started arriving at
> the destination as EF like they were supposed to be.
>
> I don't understand why a lack of CoS config would reset DSCP markings
> for traffic that is already marked when it hits the router. Could it
> be that since there were no ingress classifiers, the traffic was not
> put into a forwarding class, so the rewrite rules on egress re-marked
> it? That just occurred to me. I'm going to go check the rewrites rules
> we have applied on egress to see if that is what was happening. I was
> under the bad assumption that traffic already marked would traverse
> the router unchanged.
>
> Thanks,
> John
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