This should work properly. The COS received on a port should be mapped using cos-dscp map globally defined in the switch and that dscp is used to traverse through the backplane of the switch. This is an internal DSCP Only. WHen it reaches the egress port, using DSCP-Cos maps the internal dscp is converted back to COS. If these maps are set correctly, your COS value of the packet should remain same regardless of the trunking set on ingress and egress ports.

HTH

Sankar

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