52-4
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 52 Configuring QoS
Understanding How QoS Works
Figure 52-1 Traffic Flow Through QoS Features with PFC3
Note PFC3 can provide Layer 3 switching for the WAN traffic. PFC3 can provide QoS for the ingress WAN
traffic that is forwarded in the software by MSFC3. PFC3 can provide QoS for the egress WAN traffic
that entered the switch through a LAN port or that was forwarded in the software by MSFC3.
Figure 52-2 Traffic Flow Through QoS Features with PFC and PFC2
Note • PFC or PFC2 can provide Layer 3 switching for the ingress WAN traffic.
• PFC or PFC2 does not provide QoS for the WAN traffic. With PFC or PFC2, PFC QoS does not
change the ToS byte in the WAN traffic.
• Ingress LAN traffic that is Layer 3 switched does not go through the Multilayer Switch Feature Card
(MSFC or MSFC2) and retains the CoS value that is assigned by the Layer 3 switching engine.
• Enter the show port capabilities command to see the queue structure of a port (for more
information, see the “Receive Queues” section on page 52-13 and the “Transmit Queues” section on
page 52-28).
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