sFlow | 847The sflow sample-rate command, when issued in CONFIGURATION mode, changes the defaultsampling rate. By default, the sampling rate of an interface is set to the same value as the current globaldefault sampling rate.If the value entered is not a correct power of 2, the command generates an errormessage with the previous and next power-of-2 value. Select one of these two number and re-enter thecommand. (For more information on values in power-of-2, see Sub-sampling on page 847.)The sample rate can be configured globally or by interface using the sample rate command:Sub-samplingSub-sampling is available only on platform: etThe sFlow sample rate is not the frequency of sampling, but the number of packets that are skipped beforethe next sample is taken. Although a sampling rate can be configured for each port, TeraScale line cardscan support only a single sampling rate per port-pipe.Therefore, sFlow Agent uses sub-sampling to create multiple sampling rates per port-pipe. To achievedifferent sampling rates for different ports in a port-pipe, sFlow Agent takes the lowest numerical value ofthe sampling rate of all the ports within the port-pipe, and configures all ports to this value. sFlow Agent isthen able to skip samples on ports where you require a larger sampling rate value.Sampling rates are configurable in powers of two. This allows the smallest sampling rate possible to beconfigured on the hardware, and also allows all other sampling rates to be available through sub-sampling.For example, if Gig 1/0 and 1/1 are in a port-pipe, and they are configured with a sampling rate of 4096 oninterface Gig 1/0, and 8192 on Gig 1/1, 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. Configure interface Gig 1/0 to a sub-sampling rate of 1 to achieve an actual rate of 4096.3. Configure interface Gig 1/1 to a sub-sampling rate of 2 to achieve an actual rate of 8192.Note the absence of a configured rate in the equation. That is because when the hardware sampling ratevalue on the port-pipe exceeds the configured sampling rate value for an interface, the actual rate changesto the hardware rate. The sub-sampling rate never goes below a value of one.Command Syntax Command Mode Usage[no] sflow sample-ratesample-rateCONFIGURATIONorINTERFACEChange the global or interface sampling rate. Rate mustbe entered in factors of 2 (eg, 4096, 8192).sample-rate range:256-8388608 for C-Series and S-Series2-8388608 for E-SeriesNote: Sampling rate backoff can change the sampling rate value that is set in the hardware. This equationshows the relationship between actual sampling rate, sub-sampling rate, and the hardware sampling ratefor an interface:Actual sampling rate = sub-sampling rate * hardware sampling rate
