Converged Enhanced Ethernet Administrator's Guide v6.4.0 (53-1001761-01, June 2010)

Converged Enhanced Ethernet Administrator’s Guide 99
53-1001761-01
Congestion control
9
DRAFT: BROCADE CONFIDENTIAL
consume the full buffer memory. Thresholds can also be used to bound the maximum queueing
delay for each traffic class. Additionally if the sum of the thresholds for a port is set below 100
percent of the buffer memory, then you can also ensure that a single port does not monopolize the
entire shared memory pool.
FIGURE 9 Queue depth
The tail drop algorithm can be extended to support per priority drop thresholds. When the ingress
port CoS queue depth breaches a threshold, then any frame arriving with the associated priority
value will be dropped. Figure 9 describes how you can utilize this feature to ensure lower priority
traffic cannot totally consume the full buffer memory. Thresholds can also be used to bound the
maximum queueing delay for each traffic class. Additionally if the sum of the thresholds for a port
is set below 100 percent of the buffer memory then you can also ensure that a single CoS does not
monopolize the entire shared memory pool allocated to the port.
Changing the Tail Drop threshold
Perform the following steps from Privileged EXEC mode to change the Tail Drop threshold.
1. Enter global configuration mode.
switch#configure terminal
2. Change the Tail Drop threshold for each multicast traffic class. In this example, 1000pkt is
used.
switch(config)#qos rcv-queue multicast threshold 1000 1000 1000 1000
Example of increasing multicast frame expansion Tail Drop Threshold to 1000pkt for each multicast Traffic
Class.
switch:admin>cmsh
switch>enable
switch#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
switch(config)#qos rcv-queue multicast threshold 1000 1000 1000 1000
switch(config)#end
3. Enter the copy command to save the running-config file to the startup-config file.