52-12
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 52 Configuring QoS
Understanding How QoS Works
Ethernet Ingress Port Marking, Scheduling, Congestion Avoidance, and
Classification
These sections describe the Ethernet ingress port marking, scheduling, congestion avoidance, and
classification:
• Overview, page 52-12
• Marking at Untrusted Ports, page 52-13
• Marking at Trusted Ports, page 52-13
• Ethernet Ingress Port Scheduling and Congestion Avoidance, page 52-13
• Receive Queues, page 52-13
• Ingress Scheduling, page 52-14
• Ingress Congestion Avoidance, page 52-14
• Ethernet Ingress Port Classification Features with a Layer 3 Switching Engine, page 52-15
Overview
The trust state of an Ethernet port determines how it marks, schedules, and classifies the received traffic,
and whether or not congestion avoidance is implemented. You can configure the trust state of each port
with one of these keywords:
• untrusted (default)
• trust-ipprec (Layer 3 switching engine only—not supported on 1q4t ports except Gigabit Ethernet)
• trust-dscp (Layer 3 switching engine only—not supported on 1q4t ports except Gigabit Ethernet)
• trust-cos
Note On 1q4t ports (except Gigabit Ethernet), the trust-cos port keyword displays an error message, activates
the receive queue drop thresholds, and—as indicated by the error message—does not apply the trust-cos
trust state to the traffic. You must configure the trust-cos ACL that matches the ingress traffic to apply
the trust-cos trust state.
For more information, see the “Configuring the Trust State of a Port” section on page 52-41.
In addition to the port configuration keywords that are listed above, with a Layer 3 switching engine,
QoS uses the trust-ipprec, trust-dscp, and trust-cos ACE keywords. Do not confuse the ACE keywords
with the port keywords.
The ports that are configured with the untrusted keyword are called “untrusted ports.” The ports that are
configured with the trust-ipprec, trust-dscp, or trust-cos keywords are called “trusted ports.” QoS
implements ingress port congestion avoidance only on the ports that are configured with the trust-cos
keyword.
Ingress port marking, scheduling, and congestion avoidance use the Layer 2 CoS values. Ingress port
marking, scheduling, and congestion avoidance do not use or set the Layer 3 IP precedence or DSCP
values.
To Next Page
Loading...
Need help?
General