HP Cisco Catalyst Blade Switch 3020 Cisco Catalyst Blade Switch 3020 for HP Co - Page 223
mls qos rewrite ip dscp
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Chapter 2 Cisco Catalyst Blade Switch 3020 for HP Cisco IOS Commands mls qos rewrite ip dscp mls qos rewrite ip dscp Use the mls qos rewrite ip dscp global configuration command to configure the switch to change (rewrite) the Differentiated Services Code Point (DSCP) field of an incoming IP packet. Use the no form of this command to configure the switch to not modify (rewrite) the DSCP field of the packet and to enable DSCP transparency. mls qos rewrite ip dscp no mls qos rewrite ip dscp Syntax Description This command has no arguments or keywords. Defaults DSCP transparency is disabled. The switch changes the DSCP field of the incoming IP packet. Command Modes Global configuration Command History Release 12.2(25)SEF Modification This command was introduced. Usage Guidelines DSCP transparency affects only the DSCP field of a packet at the egress. If DSCP transparency is enabled by using the no mls qos rewrite ip dscp command, the switch does not modify the DSCP field in the incoming packet, and the DSCP field in the outgoing packet is the same as that in the incoming packet. By default, DSCP transparency is disabled. The switch modifies the DSCP field in an incoming packet, and the DSCP field in the outgoing packet is based on the quality of service (QoS) configuration, including the port trust setting, policing and marking, and the DSCP-to-DSCP mutation map. Regardless of the DSCP transparency configuration, the switch modifies the internal DSCP value of the packet that the switch uses to generate a class of service (CoS) value representing the priority of the traffic. The switch also uses the internal DSCP value to select an egress queue and threshold. For example, if QoS is enabled and an incoming packet has a DSCP value of 32, the switch might modify the internal DSCP value based on the policy-map configuration and change the internal DSCP value to 16. If DSCP transparency is enabled, the outgoing DSCP value is 32 (same as the incoming value). If DSCP transparency is disabled, the outgoing DSCP value is 16 because it is based on the internal DSCP value. OL-8916-01 Cisco Catalyst Blade Switch 3020 for HP Command Reference 2-195