Cisco WS-SUP32-GE-3B - Supervisor Engine 32 Software Configuration Manual page 549

Chapter 38 Configuring PFC QoS
These sections describe classification and marking at trusted ingress ports:
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Ingress Classification and Marking at Trust CoS LAN Ports
You should configure LAN ports to trust CoS only if they receive traffic that carries valid Layer 2 CoS.
When an ISL frame enters the switch through a trusted ingress LAN port, PFC QoS accepts the three
least significant bits in the User field as a CoS value. When an 802.1Q frame enters the switch through
a trusted ingress LAN port, PFC QoS accepts the User Priority bits as a CoS value. PFC QoS Layer 2
remarking marks all traffic received in untagged frames with the ingress port CoS value.
On ports configured to trust CoS, PFC QoS does the following:
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Ingress Classification and Marking at Trust IP Precedence Ports
You should configure ports to trust IP precedence only if they receive traffic that carries valid Layer 3
IP precedence. For traffic from trust IP precedence ports, PFC QoS maps the received IP precedence
value to the initial internal DSCP value. Because the ingress port queues and thresholds use Layer 2 CoS,
PFC QoS does not implement ingress port congestion avoidance on ports configured to trust IP
precedence. The PFC3B does not mark any traffic on ingress ports configured to trust IP precedence.
Ingress Classification and Marking at Trust DSCP Ports
You should configure ports to trust DSCP only if they receive traffic that carries valid Layer 3 DSCP.
Ingress port queues and thresholds use only Layer 2 CoS, and PFC QoS does not implement ingress port
congestion avoidance on ports configured to trust DSCP.
For traffic from trust DSCP ports, PFC QoS uses the received DSCP value as the initial internal DSCP
value. PFC QoS does not mark any traffic on ingress ports configured to trust received DSCP.
Classification and Marking on the PFC3B Using Service Policies and Policy Maps
PFC QoS classification and marking with service policies is not supported on interfaces where you
Note
configure PISA-accelerated features.
PFC QoS supports classification and marking with service policies that attach one policy map to these
interface types to apply ingress PFC QoS:
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You can attach one policy map to each Layer 3 interface to apply egress PFC QoS.
OL-11439-03
Ingress Classification and Marking at Trust CoS LAN Ports, page 38-15
Ingress Classification and Marking at Trust IP Precedence Ports, page 38-15
Ingress Classification and Marking at Trust DSCP Ports, page 38-15
PFC QoS maps the received CoS value in tagged trust CoS traffic to the initial internal DSCP value.
PFC QoS maps the ingress port CoS value applied to untagged trusted traffic to the initial internal
DSCP value.
PFC QoS enables the CoS-based ingress queues and thresholds to provide congestion avoidance.
See the "Understanding Port-Based Queue Types" section on page 38-19
ingress queues and thresholds.
Each ingress port (except FlexWAN interfaces)
Each EtherChannel port-channel interface
Each VLAN interface
Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY
Understanding How PFC QoS Works
for more information about
38-15