41-10
Catalyst 6000 Family Software Configuration Guide—Releases 6.3 and 6.4
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Chapter 41 Configuring QoS
Understanding How QoS Works
Ethernet Ingress Port Marking, Scheduling, Congestion Avoidance, and
Classification
These sections describe Ethernet ingress port marking, scheduling, congestion avoidance, and
classification:
•
Overview, page 41-10
•
Marking at Untrusted Ports, page 41-11
•
Marking at Trusted Ports, page 41-11
•
Ethernet Ingress Port Scheduling and Congestion Avoidance, page 41-11
•
Receive Queues, page 41-11
•
Ingress Scheduling, page 41-11
•
Ingress Congestion Avoidance, page 41-11
•
Ethernet Ingress Port Classification Features with a Layer 3 Switching Engine, page 41-13
Overview
The trust state of an Ethernet port determines how it marks, schedules, and classifies 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
•
1q4t
ports (except Gigabit Ethernet) do not support the
trust-ipprec
and
trust-dscp
port keywords.
You must configure a
trust-ipprec
or
trust-dscp
ACL that matches the ingress traffic to apply the
trust-ipprec
or
trust-dscp
trust state.
•
On
1q4t
ports (except Gigabit Ethernet), the
trust-cos
port keyword displays an error message,
activates receive queue drop thresholds, and—as indicated by the error message—does not apply
the
trust-cos
trust state to traffic. You must configure a
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 41-32
.
In addition to the port configuration keywords listed above, with a Layer 3 switching engine, QoS uses
trust-ipprec
,
trust-dscp
, and
trust-cos
ACE keywords. Do not confuse the ACE keywords with the port
keywords.
Ports configured with the
untrusted
keyword are called untrusted ports. Ports configured with the
trust-ipprec
,
trust-dscp
, or
trust-cos
keywords are called trusted ports. QoS implements ingress port
congestion avoidance only on ports configured with the
trust-cos
keyword.
Ingress port marking, scheduling, and congestion avoidance use Layer 2 CoS values. Ingress port
marking, scheduling, and congestion avoidance do not use or set Layer 3 IP precedence or DSCP values.