Cisco WS-SUP32-GE-3B - Supervisor Engine 32 Software Configuration Manual page 537

Chapter 38 Configuring PFC QoS
Figure 38-1
Switching
Module
1
1
The PFC QoS features are applied in this order:
Ingress port PFC QoS features:
1.
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2. PFC QoS features (not supported with PISA-accelerated features):
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Egress Ethernet LAN port QoS features:
3.
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OL-11439-03
PFC QoS Feature Processing Overview
PISA
2 2
PFC
Switching
Module
3
3
Port trust state—In PFC QoS, trust means to accept as valid and use as the basis of the initial
internal DSCP value. Ports are untrusted by default, which sets the initial internal DSCP value
to zero. You can configure ports to trust received CoS,
Layer 2 CoS remarking—PFC QoS applies Layer 2 CoS remarking, which marks the incoming
frame with the port CoS value, in these situations:
—If the traffic is not in an
—If a port is configured as untrusted.
Congestion avoidance—If you configure an Ethernet LAN port to trust CoS, QoS classifies the
traffic on the basis of its Layer 2 CoS value and assigns it to an ingress queue to provide
congestion avoidance.
Internal DSCP—On the PFC3B, QoS associates an internal DSCP value with all traffic to
classify it for processing through the system. There is an initial internal DSCP based on the
traffic trust state and a final internal DSCP. The final internal DSCP can be the same as the
initial value or an MQC policy map can set it to a different value.
MQC policy maps—MQC policy maps can do one or more of these operations:
—Change the trust state of the traffic (bases the internal DSCP value on a different
—Set the initial internal DSCP value (only for traffic from untrusted ports)
—Mark the traffic
—Police the traffic
Layer 3 DSCP marking with the final internal DSCP (optional)
Layer 2 CoS marking mapped from the final internal DSCP
Layer 2 CoS-based congestion avoidance.
Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY
ISL, 802.1Q, or 802.1p frame.
Understanding How PFC QoS Works
IP precedence, or DSCP.
QoS label)
38-3