Users Guide

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The following shows the show qos statistics output on the port extender.
DELL#show qos statistics peGigE 0/1/1
Interface peGigE 0/1/1
Queue# Matched Pkts
0 0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
DELL#show qos statistics wred-profile peGigE 0/1/1
Interface peGigE 0/1/1
Drop-statistic Dropped Pkts
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Displaying egress-queue Statistics
To display the number of transmitted and dropped packets on the egress queues of a WRED-configured interface, use the
following command.
• Display the number of packets and number of bytes on the egress-queue profile.
EXEC Privilege mode
show qos statistics egress-queue
Explicit Congestion Notification
Explicit Congestion Notification (ECN) enhances and extends WRED functionality by marking packets for later transmission
instead of dropping them when a threshold value is exceeded. Use ECN for WRED to reduce the packet transmission rate in a
congested, heavily-loaded network.
While WRED drops packets to indicate congestion, ECN marks packets instead of dropping them when the average queue
length exceeds the threshold value. ECN provides an improved method for congestion avoidance by allowing the switch to
mark packets for later transmission rather than dropping them from a queue.
ECN uses a two-bit ECN-specific field in the IP header to indicate if a packet is ECN-capable, if the endpoints in the transport
protocol are ECN-capable, and if there is network congestion.
When ECN for WRED is enabled, if the queue length is between the minimum threshold and the maximum threshold, one of
the following actions is taken:
• If the WRED drop precedence determines that the packet should be dropped but the ECN field in the packet header
indicates that the endpoints are ECN-capable, the packet is marked with a congestion-experienced (CE) bit and transmitted.
• If the ECN field indicates that both endpoints are not ECN-capable, the packet can be dropped according to the configured
WRED drop precedence.
• If the ECN field indicates a network congestion condition, the packet is marked with a congestion-experienced (CE) bit and
then transmitted.
If the queue length falls below the minimum threshold or exceeds the maximum threshold, the same WRED treatment is
applied as when ECN is not enabled:
• If queued packets fall below the minimum threshold, they are transmitted.
Quality of Service (QoS) 779