Priority Shaper

Earlier, when the priority of a queue at Per-Hop Behavior (PHB) was propagated all the way up the hierarchy towards the channel level, the PHB classes that had priority at PHB level would only be prioritized over other classes of subchannels. To avoid this, Priority Shaper feature is implemented.

Priory Shaper feature helps to balance the packet drops between the streams when multiple steams egress out of a priority queue. Egress QoS policy is supported on Priority Shaper.

Restrictions for Priority Shaper

  • Priority Shaper is supported only for PHB level classes.

  • Egress QoS Policy map with Priority Shaper can be applied only on the member interface of port channel and not at the logical level.

  • Policer configuration is not supported with the Priority Shaper configuration under same class map.

  • Priority Traffic Latency is increased during congestion with Priority Shaper configuration at Q level. Configure the queue limit with a lesser value for the priority queue to reduce the latency of priority traffic.

  • If the packet is from a 10G interface to a 1G interface, the burstiness is introduced. Due to this, dequeuing rate of this strict priority queue may be sometimes more than enqueuing. As a result, very few packet counters are seen in other queues.

Configuring Priority Shaper

Perform the following steps to configure Priority Shaper.

Procedure

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

class-map class-map-name

Example:

Device(config)#class-map class_priority

Configures class map and specifies the name of the class map to be created.

Step 4

policy-map policy-map-name

Example:

Device(config)#policy-map shape_priority

Configures the policy map.

Step 5

class class-map-name

Example:

Device(config-pmap)#class class_priority

Specifies the name of the class whose policy you want to create and enters policy-map class configuration mode. This class is associated with the class map that is created earlier.

Step 6

priority level <level 1/2 > percent <percentage 1-100 > or priority level <level 1/2> <kbps> <burst size>

Example:

Device(config-pmap-c)# priority <1-10000000> Kilo Bits per second
Device(config-pmap-c)# priority Percent <1-100>
Device(config-pmap-c)# priority level <1-2> <1-10000000> Kilo Bits per second
Device(config-pmap-c)# priority level <1-2> percent <1-100>

Assigns priority to a traffic class at the priority level specified.

Note 
level is the level of priority assigned to the priority class. Valid values are 1 (high priority) and 2 (low priority). The default value is 1. Do not specify the same priority level for two different classes in the same policy map.
Step 7

interface interface-type interface-number

Example:

Device(config)# interface gigabitethernet 0/0/1

Specifies the port to attach to the policy map and allows to enter the interface configuration mode. Valid interfaces are physical ports.

Step 8

service-policy output policy-map-name

Example:

Device(config-if)# service instance 1 ethernet
Device(config-if-srv)# service-policy output shape_priority

Applies output policy to the interface.

Note 
You can also attach the service policy over the service instance.
Step 9

end

Example:

Device(config)#end

Returns to privileged EXEC mode.

Configuration Examples for Priority Shaper

This section shows sample configurations for Priority Shaper.

Example: Configuring Priority Shaper

Verifying Priority Shaper

Use the following command to verify that the Priority Shaper feature is configured on your interface.