Cisco 7609 Configuration Manual page 416

Understanding How PFC QoS Works
For all egress traffic, PFC QoS uses a configurable mapping table to derive a CoS value from the internal
DSCP value associated with traffic (see the
section on page
to be written into ISL and 802.1Q frames.
Policy Maps
Note •
•
The PFC supports filtering, marking, and policing using policy maps (see the
Map" section on page
configure a separate policy-map class for each type of received traffic.
Policy-map classes specify filtering with the following:
•
•
Policy-map classes specify actions with the following:
•
•
The PFC uses the trust state (set by the ingress LAN port configuration or by a trust policy-map class
command) to select the Layer 2 and Layer 3 PFC QoS labels that the egress port writes into the packets
and frames before it is transmitted:
•
•
Trust CoS—Sets the internal DSCP value to a mapped value based on received or port CoS. With trust
CoS, note the following:
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
32-18
32-67). PFC QoS sends the CoS value to the egress LAN ports for use in scheduling and
You can globally disable marking and policing with the mls qos queueing-only command (see the
Enabling Queueing-Only Mode, page
You can disable marking and policing on a per-interface basis with the no mls qos interface
command (see the "Enabling or Disabling PFC Features on an Interface" section on page
32-42). Each policy map can contain multiple policy-map classes. You can
Cisco IOS access control lists (optional for IP, required for IPX and MAC-Layer filtering)
Class-map match commands for Layer 3 IP precedence and DSCP values
(Optional) Policy-map class trust commands. If specified, PFC QoS applies the policy-map class
trust state to matched traffic. Policy-map class trust states supersede ingress LAN port trust states.
Note If traffic matches a policy-map class that does not contain a trust command, the trust state
remains as set on the ingress LAN port.
(Optional) Aggregate and microflow policers, which can use bandwidth limits to either mark or drop
both conforming and nonconforming traffic. See the
page 32-16.
Trust IP precedence—Sets the internal DSCP value to a mapped value based on received IP
precedence (see the "Mapping Received IP Precedence Values to Internal DSCP Values" section on
page 32-67).
Trust DSCP—Sets the internal DSCP value to the received DSCP value.
Received CoS is overwritten with port CoS in traffic received through ports not configured to
–
trust CoS.
Received CoS is preserved only in traffic received through ports configured to trust CoS.
–
Port CoS is applied to all traffic received in untagged frames, regardless of the port trust state.
–
For information about mapping, see the
–
Values" section on page
"Mapping Internal DSCP Values to Egress CoS Values"
32-34).
"PFC Marking and Policing" section on
"Mapping Received CoS Values to Internal DSCP
32-66.
Chapter 32 Configuring PFC QoS
32-51.
"Configuring a Policy
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