Specifications

Using sFlow
ExtremeWare XOS 11.0 Concepts Guide 145
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 sent to the CPU per second.
You can also configure how frequently packets are sampled per port.
Polling Interval. Each sFlow 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. 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>
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
show sflow {configuration} command as the 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.
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>
Unconfiguring sFlow
You can reset the any configured values for sFlow to their default values and remove from sFlow any
configured collectors and ports by using the following command:
unconfigure sflow