PFC and DFC QoS Features, Port Trust, 42-8

Chapter 42 Configuring PFC QoS

Understanding How PFC QoS Works

Port Trust

In PFC QoS, trust means to accept as valid and use as the basis of the initial internal DSCP value. You can configure ports as untrusted or you can configure them to trust these QoS values:

•Layer 2 CoS

–A port configured to trust CoS is called a trust CoS port.

–Traffic received through a trust CoS port or configured by a policy map to trust CoS is called trust CoS traffic.

Note Not all traffic carries a CoS value. Only ISL, 802.1Q, and 802.1P traffic carries a CoS value. PFC QoS applies the port CoS value to any traffic that does not carry a CoS value. On untrusted ports, PFC QoS applies the port CoS value to all traffic, overwriting any received CoS value.

•IP precedence

–A port configured to trust IP precedence is called a trust IP precedence port.

–Traffic received through a trust IP precedence port or configured by a policy map to trust IP precedence is called trust IP precedence traffic.

•DSCP

–A port configured to trust DSCP is called a trust DSCP port.

–Traffic received through a trust DSCP port or configured by a policy map to trust DSCP is called trust DSCP traffic.

Traffic received through an untrusted port is called untrusted traffic.

Ingress Congestion Avoidance

PFC QoS implements congestion avoidance on trust CoS ports. On a trust CoS port, QoS classifies the traffic on the basis of its Layer 2 CoS value and assigns it to an ingress queue to provide congestion avoidance. In Release 12.2(18)SXF5 and later releases, you can configure WS-X6708-10GE trust DSCP ports to use received DSCP values for congestion avoidance. See the “Ingress Classification and Marking at Trust CoS LAN Ports” section on page 42-17for more information about ingress congestion avoidance.