Quality of Service | 861
Create a QoS Policy
There are two types of QoS policies: input and output.
Input QoS policies regulate Layer 3 and Layer 2 ingress traffic. The regulation mechanisms for input QoS
policies are rate policing and setting priority values. There are two types of input QoS policies: Layer 3 and
Layer 2.
• Layer 3 QoS input policies allow you to rate police and set a DSCP or dot1p value.
• Layer 2 QoS input policies allow you to rate police and set a dot1p value.
Output QoS policies regulate Layer 3 egress traffic. The regulation mechanisms for output QoS policies
are rate limiting, rate shaping, and WRED.
Create an input QoS policy
To create an input QoS policy:
1. Create a Layer 3 input QoS policy using the command
qos-policy-input from CONFIGURATION
mode. Create a Layer 2 input QoS policy by specifying the keyword
layer2 after the command
qos-policy-input.
2. Once you create an input QoS policy, do one or more of the following:
• Configure policy-based rate policing
• Set a DSCP value for egress packets
• Set a dot1p value for egress packets
Configure policy-based rate policing
Rate police ingress traffic using the command rate-police from QOS-POLICY-IN mode.
Set a DSCP value for egress packets
Set a DSCP value for egress packets based on ingress QoS classification, as shown in Figure 41-2. The 6
bits that are used for DSCP are also used to identify the queue in which traffic is buffered. When you set a
DSCP value, FTOS displays an informational message advising you of the queue to which you should
apply the QoS policy (using the command
service-queue from POLICY-MAP-IN mode). If you apply the
QoS policy to a queue other than the one specified in the informational message, FTOS replaces the first 3
bits in the DSCP field with the queue ID you specified.
Note: When changing a "service-queue" configuration in a QoS policy map, all QoS rules are deleted and
re-added automatically to ensure that the order of the rules is maintained. As a result, the Matched
Packets value shown in the "show qos statistics" command is reset.
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