Cisco WS-SUP32-GE-3B Software Configuration Guide - Page 550

Understanding How PFC QoS Works Chapter 38 Configuring PFC QoS Each policy map can contain multiple policy-map classes. You can configure a separate policy-map class for each type of traffic handled by the interface. There are two ways to configure filtering in policy-map classes: • Access control lists (ACLs) • Class-map match commands for IP precedence and DSCP values Policy-map classes specify actions with the following optional commands: • Policy-map set commands-For untrusted traffic or if ignore port trust is enabled, PFC QoS can use configured IP precedence or DSCP values as the final internal DSCP value. The "IP Precedence and DSCP Values" section on page 38-44 shows the bit values for IP precedence and DSCP. • Policy-map class trust commands-PFC QoS applies the policy-map class trust state to matched ingress traffic, which then uses the trusted value as the basis of its initial internal DSCP value, instead of the QoS label that was trusted at the port (if any). In a policy map, you can trust CoS, IP precedence, or DSCP. Note A trust CoS policy map cannot restore received CoS in traffic from untrusted ports. Traffic from untrusted ports always has the port CoS value. • Aggregate and microflow policers-PFC QoS can use policers to either mark or drop both conforming and nonconforming traffic. Classification and Marking on the PISA Some traffic is routed in software on the PISA. PFC QoS sends IP traffic to the PISA with the final internal DSCP values. CoS is equal to IP precedence in all traffic sent from the PISA to egress ports. Figure 38-7 Marking with PFC3B and PISA From PFC Programmable Intelligent Services Accelerator (PISA) marking IP traffic Yes from PFC? No Write ToS byte into packet Process traffic 182575 CoS = IP precedence for all traffic (not configurable) To egress port 38-16 Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY OL-11439-03