Trunked link Cos- DSCP

Unanswered Question
Jun 6th, 2008
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Hi All,

Quick quesiton:

I have atrunked link between a Cisco 3550 and a Cisco 3750. This trunk carries a number of VLANs as well as being used as a Layer 3 OSPF link for lots of other VLANs. One of the VLANs that is trunked is the Voice VLAN.

One end of the trunk is set to "mls QOS trust dscp" and the other is set to "mls QOS Trust Cos"

All of the interfaces that connect the phone are set to "mls qos trust dscp"

Is there any reason why these are different? Should they both be using the same value or is it only locally significant? I am guessing that as long as the correct Cos-Dscp maps are in place then in doesn't matter if you use dscp or cos?

Any info much appreciated,



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Carl King Mon, 06/09/2008 - 10:33
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Let me know if you find out. I have a similar question.

Does the switching engine translate DSCP marked by a host to COS automatically before sending it out a trunk to a neighboring switch when using AutoQOS.


interface fa5/1

! Inbound traffic from PBX

auto qos voip trust

int gig2/1

! 2-way traffic with neighboring switch

mls qos trust cos



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