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Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 42 Configuring PFC QoS
Configuring PFC QoS
Configuring DSCP Transparency
Note • In addition to support for other IP traffic, the PFC3B and PFC3BXL support the no mls qos rewrite
ip dscp command for MPLS traffic, traffic in IP in IP tunnels, and traffic in GRE tunnels.
• The PFC3A supports the no mls qos rewrite ip dscp command for all IP traffic except MPLS traffic,
traffic in IP in IP tunnels, and traffic in GRE tunnels.
To enable DSCP transparency, which preserves the received Layer 3 ToS byte, perform this task:
When you preserve the received Layer 3 ToS byte, QoS uses the marked or marked-down CoS value for
egress queueing and in egress tagged traffic.
This example shows how to preserve the received Layer 3 ToS byte and verify the configuration:
Router# configure terminal
Router(config)# no mls qos rewrite ip dscp
Router(config)# end
Router# show mls qos | include rewrite
QoS ip packet dscp rewrite disabled globally
Router#
Enabling Queueing-Only Mode
To enable queueing-only mode on the router, perform this task:
When you enable queueing-only mode, the router does the following:
• Disables marking and policing globally
• Configures all ports to trust Layer 2 CoS
Command Purpose
Step 1
Router(config)# no mls qos rewrite ip dscp
Disables egress ToS-byte rewrite globally on the router.
Router(config)# mls qos rewrite ip dscp
Enables egress ToS-byte rewrite globally on the router.
Step 2
Router(config)# end
Exits configuration mode.
Step 3
Router# show mls qos | include rewrite
Verifies the configuration.
Command Purpose
Step 1
Router(config)# mls qos queueing-only
Enables queueing-only mode on the router.
Router(config)# no mls qos queueing-only
Disables PFC QoS globally on the router.
Note You cannot disable queueing-only mode
separately.
Step 2
Router(config)# end
Exits configuration mode.
Step 3
Router# show mls qos
Verifies the configuration.