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7.8.1.0 - Force10 Networks

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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<br />

interface Gig 1/0, and 8192 on Gig 1/1, sFlow Agent does the following:<br />

1. Configures the hardware to a sampling rate of 4096 for all ports with sFlow enabled on that port-pipe.<br />

2. Configure interface Gig 1/0 to a sub-sampling rate of 1 to achieve an actual rate of 4096.<br />

3. Configure interface Gig 1/1 to a sub-sampling rate of 2 to achieve an actual rate of 8192.<br />

Note: Sampling rate backoff can change the sampling rate value that is set in the hardware. This equation<br />

shows the relationship between actual sampling rate, sub-sampling rate, and the hardware sampling rate<br />

for an interface:<br />

Actual sampling rate = sub-sampling rate * hardware sampling rate<br />

Note the absence of a configured rate in the equation. That is because when the hardware sampling rate<br />

value on the port-pipe exceeds the configured sampling rate value for an interface, the actual rate changes<br />

to the hardware rate. The sub-sampling rate never goes below a value of one.<br />

Back-off Mechanism<br />

Back-off Mechanism is supported on platform e<br />

If the sampling rate for an interface is set to a very low value, the CPUcan get overloaded with flow<br />

samples under high-traffic conditions. In such a scenario, a binary back-off mechanism gets triggered,<br />

which doubles the sampling-rate (halves the number of samples per second) for all interfaces. The backoff<br />

mechanism continues to double the sampling-rate until CPU condition is cleared. This is as per sFlow<br />

version 5 draft. Once the back-off changes the sample-rate, users must manually change the sampling rate<br />

to the desired value.<br />

As a result of back-off, the actual sampling-rate of an interface may differ from its configured sampling<br />

rate. The actual sampling-rate of the interface and the configured sample-rate can be viewed by using the<br />

show sflow command.<br />

sFlow on LAG ports<br />

When a physical port becomes a member of a LAG, it inherits the sFlow configuration from the LAG port.<br />

Extended sFlow<br />

Extended sFlow is supported fully on platform e<br />

Platform c supports extended-switch information processing only.<br />

FTOS Configuration Guide, version <strong>7.8.1.0</strong> 713

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