Queue-Limiting - Cisco Catalyst 4500 series Administration Manual

Chapter 42 Configuring Quality of Service
Command
Step 8
Switch(config-interface)#
service-policy output policy-map-name
Step 9
Switch(config-interface)# end
Step 10
Switch# show policy-map
[policy-map-name [class
class-map-name]]
or
Switch# show policy-map interface
interface-id
Step 11
Switch# copy running-config
startup-config
To delete an existing policy map, use the no policy-map policy-map-name global configuration
command. To delete an existing class, use the no class class-name policy-map configuration command.
To disable the priority queue, use the no priority policy-map-class configuration command.
This example shows how to configure a class-level policy called policy1. Class 1 is configured as the
priority queue, which is serviced first until it is empty.
Switch# configure terminal
Switch(config)# policy-map policy1
Switch(config-pmap)# class class1
Switch(config-pmap-c)# priority
Switch(config-pmap-c)# exit
Switch(config-pmap)# exit
Switch(config)# interface gigabitethernet1/1
Switch(config-if)# service-policy output policy1
Switch(config-if)# end
Switch #
Switch# show policy-map policy1
Policy Map policy1

Queue-limiting

When a class-based queue is instantiated on a physical port, it is set up with a default size. This size
represents the number of queue entries in which packets belonging to that class of traffic can be queued.
The scheduler moves packets from the queue that are ready for transmission, based on the queue shape,
bandwidth, and priority configuration.
The queue-limit provides the maximum number of packets that can be in the queue at any given time.
When the queue is full, an attempt to enqueue any further packets results in tail drop. However, if
dynamic buffer limiting (DBL) is enabled on the queue, packets get a probabilistic drop based on the
DBL algorithm, even when the queue is not full.
The queue-limit command can be configured under a class only when queue scheduling, such as
bandwidth, shape, or priority is already configured. The only exception to this requirement is the support
of the stand-alone queue-limit command on the class-default class.
OL_28731-01
Class class1
priority
Purpose
Specifies the policy-map name, and apply it a physical interface.
Returns to privileged EXEC mode.
Verifies your entries.
(Optional) Saves your entries in the configuration file.
Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)E
Configuring VSS QoS
42-31