Understanding How Pfc Qos Works - Cisco 7609 Configuration Manual

Configuring PFC QoS
This chapter describes how to configure quality of service (QoS) as implemented on the policy feature
card (PFC) on the Cisco 7600 series routers.
Note For complete syntax and usage information for the commands used in this publication, refer to the
Cisco 7600 Series Router Cisco IOS Command Reference publication.
This chapter contains these sections:
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Understanding How PFC QoS Works

Typically, networks operate on a best-effort delivery basis, which means that all traffic has equal priority
and an equal chance of being delivered in a timely manner. When congestion occurs, all traffic has an
equal chance of being dropped.
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Understanding How PFC QoS Works, page 32-1
PFC QoS Default Configuration, page 32-25
PFC QoS Configuration Guidelines and Restrictions, page 32-31
Configuring PFC QoS, page 32-33
With Release 12.1(13)E and later releases and with an MSFC2, you can configure Network-Based
Application Recognition (NBAR) on Layer 3 interfaces instead of using PFC QoS.
All ingress and egress traffic on an interface that is configured with NBAR is processed in software
on the MSFC2.
The PFC2 provides hardware support for input ACLs on ports where you configure NBAR.
When PFC QoS is enabled, the traffic through ports where you configure NBAR passes through the
ingress and egress queues and drop thresholds. When PFC QoS is enabled, the MSFC2 sets egress
CoS equal to egress IP precedence.
After passing through an ingress queue, all traffic is processed in software on the MSFC2 on
interfaces where you configure NBAR.
To configure NBAR, refer to this publication:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t8/dtnbarad.htm
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
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