Configuration Considerations - Brocade Communications Systems FastIron Administration Manual

for one of the ports are sent after ten seconds, and counter data for the other port are sent after an
additional ten seconds. Ten seconds later, new counter data for the first port are sent. Similarly, if sFlow
is enabled on five ports and the polling interval is 20 seconds, the Brocade device sends counter data
every four seconds.
The default polling interval is 20 seconds. You can change the interval to a value from 0 to 4294967295
seconds. The interval value applies to all interfaces on which sFlow is enabled. If you set the polling
interval to 0, counter data sampling is disabled.
To change the polling interval, enter a command such as the following at the global CONFIG level of the
CLI.
device(config)#sflow polling-interval 30
Syntax: [no] sflow polling-interval secs
The secs parameter specifies the interval and can be from 0 through 4294967295 seconds. The default
is 20 seconds. If you specify 0, counter data sampling is disabled.
Changing the sampling mode
On all devices other than the Brocade ICX 7750, Brocade ICX 7450, and Brocade ICX 7250, by default,
only the non-dropped packets are included for sFlow sampling.
The dropped packets are not included in the sFlow samples that are sent to the sFlow collector. The
sampling mode can be changed to include the dropped packets using the sflow sample-mode
command.
NOTE
The sflow sample-mode command is not supported on Brocade ICX 7750, Brocade ICX 7450,
Brocade ICX 7250, Brocade ICX 6430, Brocade ICX 6650, and FSX 800/1600 devices.
Changing the sampling rate
The sampling rate is the average ratio of the number of packets incoming on an sFlow-enabled port, to
the number of flow samples taken from those packets.
You can change the default (global) sampling rate. You also can change the rate on an individual port,
overriding the default sampling rate of 4096. With a sampling rate of 4096, on average, one in every
4096 packets forwarded on an interface is sampled.

Configuration considerations

The sampling rate is a fraction in the form 1/N, meaning that, on average, one out of every N packets
will be sampled. The sflow sample command at the global level or port level specifies N, the
denominator of the fraction. Thus a higher number for the denominator means a lower sampling rate
since fewer packets are sampled. Likewise, a lower number for the denominator means a higher
sampling rate because more packets are sampled. For example, if you change the denominator from
512 to 128, the sampling rate increases because four times as many packets will be sampled.
NOTE
Brocade recommends that you do not change the denominator to a value lower than the default.
Sampling requires CPU resources. Using a low denominator for the sampling rate can cause high CPU
utilization.
FastIron Ethernet Switch Administration Guide
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Changing the sampling mode
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