Network Router User Manual

42-16
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 42 Configuring PFC QoS
Understanding How PFC QoS Works
Understanding Classification and Marking
The following sections describe where and how classification and marking occur on the Cisco 7600
series routers:
• Classification and Marking at Trusted and Untrusted Ingress Ports, page 42-16
• Classification and Marking at Ingress OSM Ports, page 42-17
• Classification and Marking on the PFC Using Service Policies and Policy Maps, page 42-18
• Classification and Marking on the MSFC, page 42-19
Classification and Marking at Trusted and Untrusted Ingress Ports
The trust state of an ingress port determines how the port marks, schedules, and classifies received
Layer 2 frames, and whether or not congestion avoidance is implemented. These are the port trust states:
• Untrusted (default)
• Trust IP precedence
• Trust DSCP
• Trust CoS
In all releases, ingress LAN port classification, marking, and congestion avoidance can use Layer 2 CoS
values and do not set Layer 3 IP precedence or DSCP values.
In Release 12.2(18)SXF5 and later releases, you can configure WS-X6708-10GE ports to use received
DSCP values for ingress LAN port classification and congestion avoidance (see the “Configuring
DSCP-Based Queue Mapping” section on page 42-98)
In Releases earlier than Release 12.2(18)SXF5, ingress LAN port classification, marking, and
congestion avoidance use Layer 2 CoS values only.
The following sections describe classification and marking at trusted and untrusted ingress ports:
• Classification and Marking at Untrusted Ingress Ports, page 42-16
• Ingress Classification and Marking at Trusted Ports, page 42-16
Classification and Marking at Untrusted Ingress Ports
PFC QoS Layer 2 remarking marks all frames received through untrusted ports with the port CoS value
(the default is zero).
To map the port CoS value that was applied to untrusted ingress traffic to the initial internal DSCP value,
configure a trust CoS policy map that matches the ingress traffic.
Ingress Classification and Marking at Trusted Ports
You should configure ports to trust only if they receive traffic that carries valid QoS labels. QoS uses the
received QoS labels as the basis of initial internal DSCP value. After the traffic enters the router, you
can apply a different trust state to traffic with a policy map. For example, traffic can enter the router
through a trust CoS port, and then you can use a policy map to trust IP precedence or DSCP, which uses
the trusted value as the basis of the initial internal DSCP value, instead of the QoS label that was trusted
at the port.