Extreme Networks ExtremeWare XOS Guide Manual page 212

Status Monitoring and Statistics
Additional sFlow Configuration Options
There are three global options that you can configure to different values from the defaults. These affect
how frequently the sFlow data is sent to the remote collector, how frequently packets are sampled, and
the maximum number of sFlow samples that could be processed in the CPU per second.
You can also configure how frequently packets are sampled per port.
Polling Interval. Each port counter is periodically polled to gather the statistics to send to the collector. If
there is more than one counter to be polled, the polling is distributed in such a way that each counter is
visited once during each polling interval, and the data flows are spaced in time. For example, assume
that the polling interval is 20 seconds and there are 40 counters to poll. Two ports will be polled each
second, until all 40 are polled. To configure the polling interval, use the following command:
configure sflow poll-interval <seconds>
Global Sampling Rate. This is the rate that newly enabled sFlow ports will have their sample rate set to.
Changing this rate will not affect currently enabled sFlow ports. The default sample rate is 8192, so by
default sFlow samples one packet out of every 8192 received. You configure the switch to use a different
sampling rate with the following command:
configure sflow sample-rate <number>
For example, if you set the sample rate number to 16384, the switch samples one out of every 16384
packets received. Higher numbers mean fewer samples and longer times between samples. If you set
the number too low, the number of samples can be very large, which increases the load on the switch.
Do not configure the sample rate to a number lower than the default unless you are sure that the traffic
rate on the source is low.
Per Port Sampling Rate. You can set the sampling rate on individual ports, using the following
command:
configure sflow ports <portlist> sample-rate <number>
For BlackDiamond 10K—At the hardware level, all ports on the same slot are sampled at the same rate,
so if one port is configured to sample less frequently than another on the same slot, the extra samples
are discarded. This is indicated in the output of the command as the
show sflow {configuration}
sub-sampling factor. For example, if one port is configured to sample one packet per every 8192 packets,
and the second port on the same slot is configured to sample one packet per every 16384 packets, the
second port will show a sub-sampling factor of two.
For Summit X450—At the hardware level, all ports on the switch are sampled at the same rate, so if one
port is configured to sample less frequently than another, the extra samples are discarded. This is
indicated in the output of the command as the sub-sampling factor. For
show sflow {configuration}
example, if one port is configured to sample one packet per every 8192 packets, and the second port on
the same slot is configured to sample one packet per every 16384 packets, the second port will show a
sub-sampling factor of two.
Maximum CPU Sample Limit. A high number of samples can cause a heavy load on the switch CPU. To
limit the load, there is a CPU throttling mechanism to protect the switch. Whenever the limit is reached,
the sample rate value is doubled on the slot from which the maximum number of samples are received.
For ports on that slot that are sampled less frequently, the sampling rate is not changed; the sub-
sampling factor is adjusted downward. To configure the maximum CPU sample limit, use the following
command:
configure sflow max-cpu-sample-limit <rate>
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ExtremeWare XOS 11.3 Concepts Guide