Brocade FastIron Ethernet Switch Administration Guide - Manual (Page 249)

the counter data to smooth performance. For example, if sFlow is enabled on two ports and the polling
interval is 20 seconds, the Brocade device sends counter data every ten seconds. The counter data 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 1 to any higher
value. 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-intervalsecs
The secs parameter specifies the interval and can be from 1 to any higher value. The default is 20
seconds. If you specify 0, counter data sampling is disabled.
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 512. With a sampling rate of 512, on average, one in every 512
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.
Configured rate and actual rate
When you enter a sampling rate value, this value is the configured rate as well as the actual sampling
rate .
Change to global rate
If you change the global sampling rate, the change is applied to all sFlow-enabled ports except those
ports on which you have already explicitly set the sampling rate. For example, suppose that sFlow is
enabled on ports 1/1, 1/2, and 5/1. If you configure the sampling rate on port 1/1 but leave the other two
ports using the default rate, then a change to the global sampling rate applies to ports 1/2 and 5/1 but
not port 1/1. sFlow assumes that you want to continue using the sampling rate you explicitly configured
on an individual port even if you globally change the sampling rate for the other ports.
Changing the sampling rate
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