From: Toh Soon, Lim (tohsoon28@gmail.com)
Date: Mon Aug 06 2007 - 19:54:08 ART
Hi Herbert,
So, the mapping is done based on DSCP values at the very beginning when the
packet enters the switch, to determine its WRED threshold when it later
exits the switch? I was under the impression (from theory in books) that we
choose the thresholds based on CoS (is this referring to the CoS that's
mapped to from the internal DSCP?), though I can't find any command to do
that. Secondly, what if I configure "mls qos trust ip-prec" on the ingress
int, can we still perform the DSCP-to-threshold mapping?
Another thing that baffles me is mapping the internal DSCP values to CoS
values for egress queueing/scheduling, where we can change the default
mapping using the global config command "mls qos map dscp-cos". What if the
packet exits a non-dot1q link, how is this CoS value carried in the packet?
Or is that CoS value just an internal value to the switch?
Appreciate any comments and guidance.
Thank you.
B.Rgds,
Lim TS
On 8/7/07, Herbert Maosa <asawilunda@googlemail.com> wrote:
>
> I believe this is used for both WRED and Tail Drop, to specify the mapping
> between DSCP values and drop thresholds.
>
> For each of the four queues, you specify two drop thresholds ( low, high
> ). Then you need to specify which DSCP values fall under either one of the
> two thresholds. This is where you use the wrr-queue dscp-map command, to map
> the DSCP values to the thresholds.
>
> Herbert.
>
>
> On 8/6/07, Toh Soon, Lim <tohsoon28@gmail.com> wrote:
>
> > Hi All,
> >
> > Does anyone know exactly how the "wrr-queue dscp-map" interface config
> > command is used on a Catalyst 3550?
> >
> > From DocCD I understand it's used on the ingress interface to map
> > trusted
> > DSCP values to WRED thresholds (1 or 2). I mean, this happens before
> > DSCP
> > mutation (if one is configured) takes action?
> >
> > If DSCP mutation is configured, regardless of what the "mutated"
> > internal
> > DSCP value is and the resultant mapped COS value is before egress
> > scheduling, the packets will be assigned to the WRED threshold which we
> > specified earlier on the ingress interface?
> >
> > Please help me understand better.
> >
> >
> > Thank you.
> >
> > B.Rgds,
> > Lim TS
> >
> > _______________________________________________________________________
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> >
>
>
>
> --
> Kindest regards,
> hm
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