Name: Cisco 7609
Brand: Cisco
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32-12

Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E

78-14064-04

Chapter 32 Configuring PFC QoS

Understanding How PFC QoS Works

Egress LAN Port Features

PFC QoS supports egress LAN port scheduling and congestion avoidance using Layer 2 CoS values.

Egress LAN port marking sets Layer 2 CoS values and Layer 3 DSCP values. See the “LAN Egress

Port Features” section on page 32-21.

Egress OSM Port Features

Ingress PFC QoS sets Layer 3 DSCP values that can be used by the OSM egress QoS features.

MSFC Features

PFC QoS marks IP traffic transmitted to the MSFC with rewritten Layer 3 DSCP values. With PFC2,

CoS is equal to IP precedence in all traffic sent from the MSFC2 to egress ports; with PFC1, CoS is zero.

Note Traffic that is Layer 3 switched does not go through the MFSC and retains the CoS value assigned by

the PFC.

Ingress LAN Port Features

These sections describe ingress LAN port PFC QoS features:

• Ingress LAN Port Trust States, page 32-12

• Marking at Untrusted Ingress LAN Ports, page 32-13

• Marking at Trusted Ingress LAN Ports, page 32-13

• Ingress LAN Port Scheduling and Congestion Avoidance, page 32-13

Ingress LAN Port Trust States

The trust state of an ingress LAN port determines how the port marks, schedules, and classifies received

Layer 2 frames, and whether or not congestion avoidance is implemented. You can configure the trust

state of each ingress LAN port as follows:

• Untrusted (default)

• Trust IP precedence (not supported on 1q4t LAN ports except Gigabit Ethernet)

• Trust DSCP (not supported on 1q4t LAN ports except Gigabit Ethernet)

• Trust CoS (not supported on 1q4t LAN ports except Gigabit Ethernet)

See the “Configuring the Trust State of Ethernet LAN and OSM Ingress Ports” section on page 32-53.

PFC QoS implements ingress LAN port congestion avoidance only on LAN ports configured to trust

CoS.

Note Ingress LAN port marking, scheduling, and congestion avoidance use Layer 2 CoS values and does not

use or set Layer 3 IP precedence or DSCP values.

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