Cisco Systems OL-4266-08 manual Understanding Classification and Marking, 42-16

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.

	Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
42-16	OL-4266-08