Cisco Systems EA6500 Manual De Usuario

Filtering for PFC QoS can use Layer 2, 3, and 4 values. Marking uses Layer 2 CoS values and Layer 3 
IP precedence or DSCP values. 

These sections describe the internal DSCP values:

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:

For trust-cos traffic, from received or ingress port Layer 2 CoS values

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

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 
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 the

 or the 

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