trusting dscp between my layer 3 ports distribution switches on campus

Unanswered Question
Sep 17th, 2010

hi all

i have an access, dist and core design with layer 3 ports between my dist and core.

what QOS setting do i need to apply on these layer 3 ports, is the mls qos dscp trust enough, or would I need to apply a policy map to the layer 3 ports ?



I have this problem too.
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Lei Tian Fri, 09/17/2010 - 03:57

Hi Carl,

Assuming packets are marked properly on access layer, trust DSCP is enough, no need to apply policy-map on distribution layer to remark packets. If the platform is cos based queueing, then you might need to modify the DSCP-COS map; otherwise, the default map will be used to get COS from DSCP.


Lei Tian

carl_townshend Fri, 09/17/2010 - 04:20

so are you saying I can use this between my distribution and core  layer 3 ports  with ip addresses on them ?

francisco_1 Fri, 09/17/2010 - 06:25


As lei mentioned, the traffic has been correctly marked previously by the access switches, therefore you do not need to make any remarking, but you need to ensure that you do trust the incoming DSCP by applying "mls trust dscp" on your distribution and core siwtch. This is the easiest case, as all ports will be marked as trust-dscp and that should be sufficient:



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