Cisco WS-X6066-SLB-APC - Content Switching Module Software Manual page 717

Chapter 41 Configuring QoS
Marking at Untrusted Ports
QoS marks all frames received through untrusted ports with the port CoS value (the default is zero). QoS
does not implement ingress port congestion avoidance on untrusted ports: the traffic goes directly to the
switching engine.
Marking at Trusted Ports
When an ISL frame enters the switch through a trusted port, QoS accepts the three least significant bits
in the User field as a CoS value. When an 802.1Q frame enters the switch through a trusted port, QoS
accepts the User Priority bits as a CoS value. QoS marks all traffic received in other frame types with
the port CoS value.
The port CoS value is configurable for each Ethernet port (for more information, see the
the CoS Value for a Port" section on page
Ethernet Ingress Port Scheduling and Congestion Avoidance
QoS does not implement ingress port congestion avoidance on ports configured with the untrusted,
trust-ipprec, or trust-dscp keywords: the traffic goes directly to the switching engine.
QoS uses CoS-value-based receive-queue drop thresholds to avoid congestion in traffic entering the
switch through a port configured with the trust-cos keyword (for more information, see the
"Configuring the Trust State of a Port" section on page
Receive Queues
Enter a show port capabilities command to see the queue structure of a port. The command displays
one of the following:
•
•
•
Strict-priority queues are serviced in preference to other queues. QoS services traffic in a strict-priority
queue before servicing the standard queue. When QoS services the standard queue, after receiving a
packet, it checks for traffic in the strict-priority queue. If QoS detects traffic in the strict-priority queue,
it suspends its service of the standard queue and completes service of all traffic in the strict-priority
queue before returning to the standard queue.
Ingress Scheduling
QoS schedules traffic through the receive queues based on CoS values. In the 1p1q4t and 1p1q0t default
configurations, QoS assigns all traffic with CoS 5 to the strict-priority queue; QoS assigns all other
traffic to the standard queue. In the 1q4t default configuration, QoS assigns all traffic to the standard
queue.
Ingress Congestion Avoidance
If a port is configured with the trust-cos keyword, QoS implements CoS-value-based receive-drop
thresholds to avoid congestion in received traffic.
78-13315-02
rx-(1p1q4t)—one strict-priority queue and one standard queue with four thresholds
rx-(1q4t)—one standard queue with four thresholds
rx-(1p1q0t)—one strict-priority queue and one standard queue with no configurable thresholds
41-33).
41-32).
Catalyst 6000 Family Software Configuration Guide—Releases 6.3 and 6.4
Understanding How QoS Works
"Configuring
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