QoS trust

Traffic priorities for networks can be carried in VLAN tags, using the CoS Priority Code Point (PCP), or in IP packet headers, using the Differentiated Services Code Point (DSCP). Whether these priorities affect how traffic is serviced depends upon which QoS trust mode is configured on the switch.

QoS trust mode specifies how the switch assigns local priority values to ingress packets. By default, the global trust mode for the switch is trust none. This means that any QoS information in the packet (CoS or DSCP) is ignored. When trust mode is set to CoS or DSCP, the switch translates the QoS settings in VLAN tags (for CoS), or the DS field in an IP header (for DSCP), to local priority values on the switch. Translation is controlled by the CoS map or DSCP map tables. For example:

Trust mode can be set globally for all interfaces, or individually for each interface. By default, trust mode is set to none, which means that local priority values are taken from the CoS map value for code point 0.