Cisco 7609 Configuration Manual page 415
Cisco ios software configuration guide—12.1e
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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
Note
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
Note
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
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Troubleshooting
