Trusting DSCP Values on trunk link

Hi All,

     I wanted to see if you guys could answer this question for me. I am trying to see if you guys believe that I require the "mls qos trust dscp" command for the inter-switch link trunk between the L2 switches as you see on the diagram below. The L2 switches are marking the packets inbound.
Diagram.jpg
vreyesiiAsked:
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TimotiStDatacenter TechnicianCommented:
I'd say it depends on:
- what are your actual goals: prioritize based on dscp on the switches or not?
- what's the direction of the packet flow?

Tamas
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vreyesiiAuthor Commented:
Prioritize based on dscp values on the switches. The dscp values are being applied inbound on all the 48 ports.  Traffic can flow either up through the layer 3 switches if both are up. Or via the trunk link if one of the layer 3 switches go down.
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TimotiStDatacenter TechnicianCommented:
In that case, if you omit the trust command on the trunk link, you won't give QOS to traffic traversing it if the relevant L3 switch is down. If this link is at least Gig, and the uplink to L3 are Gig, this shouldn't be a problem. But some best practice documents say that you should prioritize anyway, as that might give a few microseconds less latency to packets traversing.
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vreyesiiAuthor Commented:
Thank you.
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