Quality of Service (QoS) | 829Set a DSCP value for egress packets based on ingress QoS classification, as shown in Figure 39-2. The 6bits that are used for DSCP are also used to identify the queue in which traffic is buffered. When you set aDSCP value, FTOS displays an informational message advising you of the queue to which you shouldapply the QoS policy (using the command service-queue from POLICY-MAP-IN mode). If you apply theQoS policy to a queue other than the one specified in the informational message, FTOS replaces the first 3bits in the DSCP field with the queue ID you specified.Figure 39-12. Marking DSCP Values for Egress PacketsSet a dot1p value for egress packetsSet a dot1p value for egress packets using the command set mac-dot1p from QOS-POLICY-IN mode.Create an output QoS policyTo create an output QoS policy:1. Create an output QoS policy using the command qos-policy-output from CONFIGURATION mode.2. Once you configure an output QoS policy, do one or more of the following• Configure policy-based rate limiting• Configure policy-based rate shaping• Allocate bandwidth to queue• Specify WRED drop precedenceConfigure policy-based rate limitingConfigure policy-based rate limiting is supported only on platform ePolicy-based rate limiting is configured the same way as port-based rate limiting except that the commandfrom QOS-POLICY-OUT mode is rate-limit rather than rate limit as it is in INTERFACE mode.Configure policy-based rate shapingRate shape egress traffic using the command rate-shape from QOS-POLICY-OUT mode.FTOS#configFTOS(conf)#qos-policy-input my-input-qos-policyFTOS(conf-qos-policy-in)#set ip-dscp 34% Info: To set the specified DSCP value 34 (100-010 b) the QoS policy must be mapped to queue4 (100 b).FTOS(conf-qos-policy-in)#show config!qos-policy-input my-input-qos-policyset ip-dscp 34FTOS(conf-qos-policy-in)#endFTOS#
