FTOS Configuration Guide for the C-Series - Force10 Networks

Sampling Rate
The sFlow sampling rate is the number of packets that are skipped before the next sample is taken. sFlow
does not have time-based packet sampling.
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 number and re-enter the
command. (For more information on values in power-of-2, see Sub-sampling on page 308.)
The sample rate can be configured globally or by interface using the sample rate command:
Command Syntax Command Mode Usage
[no] sflow sample-rate
sample-rate
Sub-sampling
CONFIGURATION
or
INTERFACE
Sub-sampling is supported on platform e
Change the global or interface sampling rate. Rate
must be entered in factors of 2 (eg, 4096m 8192).
sample-rate range: 256-8388608 for C-Series
2-8388608 for E-Series
The sFlow sample rate is not the frequency of sampling, but the number of packets that are skipped before
the next sample is taken. Although a sampling rate can be configured for each port, TeraScale line cards
can support only a single sampling rate per port pipe.
Therefore, 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, sFlow Agent takes the lowest numerical value of
the sampling rate of all the ports within the port pipe, and configures all ports to this value. 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 allows the smallest sampling rate possible to be
configured 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 on
interface 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.
308 sFlow