•
Marking evaluates the policer and configuration information for the action to be taken when a packet is
out of profile and determines what to do with the packet (pass through a packet without modification,
marking down the QoS label in the packet, or dropping the packet).
Queueing and scheduling are only supported at egress and not at ingress on the switch.Note
Actions at Egress Port
Actions at the egress port include queueing and scheduling:
•
Queueing evaluates the QoS packet label and the corresponding DSCP or CoS value before selecting
which of the four egress queues to use. Because congestion can occur when multiple ingress ports
simultaneously send data to an egress port, WTD differentiates traffic classes and subjects the packets
to different thresholds based on the QoS label. If the threshold is exceeded, the packet is dropped.
•
Scheduling services the four egress queues based on their configured SRR shared or shaped weights.
One of the queues (queue 1) can be the expedited queue, which is serviced until empty before the other
queues are serviced.
Classification Overview
Classification is the process of distinguishing one kind of traffic from another by examining the fields in the
packet. Classification is enabled only if QoS is globally enabled on the switch. By default, QoS is globally
disabled, so no classification occurs.
During classification, the switch performs a lookup and assigns a QoS label to the packet. The QoS label
identifies all QoS actions to be performed on the packet and from which queue the packet is sent.
The QoS label is based on the DSCP or the CoS value in the packet and decides the queueing and scheduling
actions to perform on the packet. The label is mapped according to the trust setting and the packet type as
shown in Classification Flowchart, on page 548.
You specify which fields in the frame or packet that you want to use to classify incoming traffic.
Related Topics
Ingress Port Activity
Egress Port Activity
Configuring a QoS Policy, on page 584
Non-IP Traffic Classification
The following table describes the non-IP traffic classification options for your QoS configuration.
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
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Information About QoS
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