Administrator Guide

sflow polling-interval interval value
• interval value: in seconds.
The range is from 15 to 86400 seconds.
The default is 20 seconds.
Changing the Sampling Rate
The sflow sample-rate command, when issued in CONFIGURATION mode, changes the default sampling
rate.
By default, the sampling rate of an interface is set to the same value as the current global default sampling
rate. If the value entered is not a correct power of 2, the command generates an error message with the
previous and next power-of-2 value. Select one of these two numbers and re-enter the command. (For more
information on values in power-of-2, refer to Sub-Sampling.)
To change the sampling rate either globally or on an interface, use the following command.
• Change the global or interface sampling rate.
CONFIGURATION mode or INTERFACE mode
[no] sflow sample-rate sample-rate
sample-rate: The range is from 256 to 8388608 for the C-Series and S-Series. The range is from 2 to
8388608 for the E-Series.
The rate must be entered in factors of 2 (for example, 4096 or 8192).
Sub-Sampling
The sFlow sample rate is not the frequency of sampling, but the number of packets that are skipped before
the next sample is taken.
Therefore, the sFlow agent uses sub-sampling to create multiple sampling rates per port-pipe. To achieve
different sampling rates for different ports in a port-pipe, the sFlow agent takes the lowest numerical value of
the sampling rate of all the ports within the port-pipe and configures all the ports to this value. The sFlow
agent is then able to skip samples on ports where you require a larger sampling rate value.
Sampling rates are configurable in powers of two. This configuration allows the smallest sampling rate
possible on the hardware and also allows all other sampling rates to be available through sub-sampling.
For example, if Tengig 1/0 and 1/1 are in a port-pipe, and they are configured with a sampling rate of 4096 on
interface Tengig 1/0, and 8192 on Tengig 1/1, the sFlow agent does the following:
1 Configures the hardware to a sampling rate of 4096 for all ports with sFlow enabled on that port-pipe.
2 Configures interface Tengig 1/0 to a sub-sampling rate of 1 to achieve an actual rate of 4096.
3 Configures interface Tengig 1/1 to a sub-sampling rate of 2 to achieve an actual rate of 8192.
sFlow 836