Brocade Converged Enhanced Ethernet Administrator's Guide v6.1.2_cee (53-1001258-01, June 2009)

110 Converged Enhanced Ethernet Administrator’s Guide
53-1001258-01
Congestion control
8
Example of activating the CoS-to-Traffic Class QoS map on an interface.
switch:admin>cmsh
switch>enable
switch#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
switch(config)#interface tengigabitethernet 0/2
switch(conf-if-te-0/2)#qos cos-traffic-class test
switch(conf-if-te-0/2)#exit
switch(config)#exit
switch#
Verifying a mapping CoS to traffic class
Congestion control
In this section:
•Tail drop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
•Ethernet pause . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
•Ethernet Per-Priority Pause . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Queues can begin filling up due to a number of reasons, such as over subscription of a link or
backpressure from a downstream device. Sustained, large queue buildups generally indicate
congestion in the network and can affect application performance through increased queueing
delays and packet loss.
Congestion control covers features that define how the system responds when congestion occurs
or active measures taken to prevent the network from entering a congested state.
Tail drop
Tail drop queueing is the most basic form of congestion control. Packets are queued in FIFO order
and queue buildup can continue until all buffer memory is exhausted. This is the default behavior
when no additional QoS has been configured.
Step Task Command
1 Enter global configuration mode.
switch#configure terminal
2 Create the CoS-Traffic-Class mapping
specifying a name and the mapping.
switch(config)#show qos map
cos-traffic-class test