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Cisco7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
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Chapter42 Con figuring PFC QoS
Understanding How PFCQoS Works
•Trust CoS (CoS is always zero for POS and ATM OSM ports because the port CoS value is not
configurable on POS and ATM OSM ports.)
Classification and Marking on the PFC Using Service Policies and Policy Maps
PFC QoS supports classification and marking with service policies that attach one policy map to these
interface types to apply ingress PFC QoS:
•Each ingress port (except FlexWAN interfaces)
•Each EtherChannel port-channel interface
•Each VLAN interface
With a PFC3, you can attach one policy map to each Layer 3 interface (except FlexWAN interfaces) to
apply egress 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 page42-55 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—PFCQoS can use policers to either mark or drop both
conforming and nonconforming traffic.