Hi This interface command is necessary if
mls qos is enabled globally. By default, mls qos is OFF, and the switch will not change any DSCP/COS values. The moment you enable "mls qos" at global config, the Catalyst switch will automatically remark the packets to DSCP 0 unless you explicitly trust the interface (similar to DHCP snooping trust or DAI trust). This seems more of an RS-type question than SEC but it could be the basis of a really evil troubleshooting question in the lab, i.e., they enable "mls qos" globally and then we wonder why our markings are lost. In summary, if "mls qos" is not enabled globally you do not have to do anything at the interface level. If "mls qos" is enabled globally, you must configure "mls qos trust..." at the interface-level otherwise the packet will get remarked. Regards Richard
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