CoS and DSCP marking on Cat3550

From: Javier Tomé (fjtm@tid.es)
Date: Sat Oct 22 2005 - 17:46:20 GMT-3


Hi group,

Trying to understand how QoS mapping works on the 3550. I have been
searching through the archives and I don't find a clear answer to this
question. Does "mls qos map cos-dscp" actually write the DSCP value of
ip traffic going through the switch, or that mapping is just used
internally to apply QoS settings?. What about "mls qos map dscp-cos"?

In my scenario I have the following topology:

VLAN2--SW1--VLAN3--R1

SW1 is routing between both VLANs. Traffic from VLAN2 arrives with a
valid CoS and I want to mark DSCP value in such a way that a specific
policy can be applied on R1 based on that DSCP. I was trying the following:

mls qos trust cos (on FE interface of SW1 with VLAN2)
mls qos map cos-dscp

If I would also want traffic on VLAN3 to be mark with an specific CoS
value, Could I use "mls qos map dscp-cos"?

 From the documentation it seems that mls qos mapping is just internal
to the switch. If this is true, How could I go to achieve this?

Thank you in advance

Javi Tome



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