Chapter 42 Configuring PFC QoS

Understanding How PFC QoS Works

Internal DSCP Values

During processing, PFC QoS represents the priority of all traffic (including non-IP traffic) with an internal DSCP value.

Initial Internal DSCP Value

On the PFC, before any marking or policing takes place, PFC QoS derives the initial internal DSCP value as follows:

•For untrusted traffic, when ignore port trust is not enabled, PFC QoS sets the initial internal DSCP value to zero for both tagged and untagged untrusted traffic.

•For untrusted traffic, when ignore port trust is enabled, PFC QoS does the following:

–For IP traffic, PFC QoS uses the received DSCP value as the initial internal DSCP value.

–For traffic without a recognizable ToS byte, PFC QoS maps the port CoS value to the initial internal DSCP value.

•For trust CoS traffic, when ignore port trust is enabled, PFC QoS does the following:

–For IP traffic, PFC QoS uses the received DSCP value as the initial internal DSCP value.

Note For trust CoS traffic, when ignore port trust is enabled, PFC QoS does not use the received CoS value in tagged IP traffic.

–For tagged traffic without a recognizable ToS byte, PFC QoS maps the received CoS value to the initial internal DSCP value.

–For untagged traffic without a recognizable ToS byte, PFC QoS maps the port CoS value to the initial internal DSCP value.

•For trust IP precedence traffic, PFC QoS does the following:

–For IP traffic, PFC QoS maps the received IP precedence value to the initial internal DSCP value.

–For tagged traffic without a recognizable ToS byte, PFC QoS maps the received CoS value to the initial internal DSCP value.

–For untagged traffic without a recognizable ToS byte, PFC QoS maps the port CoS value to the initial internal DSCP value.

•For trust DSCP traffic, PFC QoS, PFC QoS does the following:

–For IP traffic, PFC QoS uses the received DSCP value as the initial internal DSCP value.

–For tagged traffic without a recognizable ToS byte, PFC QoS maps the received CoS value to the initial internal DSCP value.

–For untagged traffic without a recognizable ToS byte, PFC QoS maps the port CoS value to the initial internal DSCP value.

For trust CoS traffic and trust IP precedence traffic, PFC QoS uses configurable maps to derive the initial internal 6-bit DSCP value from CoS or IP precedence, which are 3-bit values.

Final Internal DSCP Value

Policy marking and policing on the PFC can change the initial internal DSCP value to a final internal DSCP value, which is then used for all subsequently applied QoS features.

 

 

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Cisco Systems OL-4266-08 manual Internal Dscp Values, Initial Internal Dscp Value, Final Internal Dscp Value, 42-11
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OL-4266-08 specifications

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