Cisco 7609 Configuration Manual page 415

Chapter 32 Configuring PFC QoS
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Filtering for PFC QoS can use Layer 2, 3, and 4 values. Marking uses Layer 2 CoS values and Layer 3
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IP precedence or DSCP values.
Internal DSCP Values
These sections describe the internal DSCP values:
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Internal DSCP Sources
During processing, PFC QoS represents the priority of all traffic (including non-IP traffic) with an
internal DSCP value. PFC QoS derives the internal DSCP value from the following:
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The trust state of traffic is the trust state of the ingress LAN port unless set otherwise by a matching ACE.
A trust-cos policer cannot restore received CoS in traffic from untrusted ingress LAN ports. Traffic from
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untrusted ingress LAN ports always has the ingress port CoS value.
PFC QoS uses configurable mapping tables to derive the internal 6-bit DSCP value from CoS or IP
precedence, which are 3-bit values (see
section on page 32-66
on page
Egress DSCP and CoS Sources
For egress IP traffic, PFC QoS creates a ToS byte from the internal DSCP value and sends it to the egress
port to be written into IP packets. For trust-dscp and untrusted IP traffic, the ToS byte includes the
original 2 least-significant bits from the received ToS byte.
The internal DSCP value can mimic an IP precedence value (see
Note
78-14064-04
Policers, page 32-19
Attaching Policy Maps, page 32-21
Egress CoS and ToS Values, page 32-21
Internal DSCP Sources, page 32-17
Egress DSCP and CoS Sources, page 32-17
For trust-cos traffic, from received or ingress port Layer 2 CoS values
Note Traffic from an untrusted ingress LAN port has the ingress port CoS value and if traffic from
an untrusted ingress Ethernet port matches a trust-cos policer, PFC QoS derives the internal
DSCP value from the ingress port CoS value.
For trust-ipprec traffic, from received IP precedence values
For trust-dscp traffic, from received DSCP values
For untrusted traffic, from ingress port CoS or configured DSCP values
or the "Mapping Received IP Precedence Values to Internal DSCP Values" section
32-67).
the"Mapping Received CoS Values to Internal DSCP Values"
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
Understanding How PFC QoS Works
Table 32-1 on page 32-5).
32-17