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FTOS Configuration Guide for the C-Series - Force10 Networks

FTOS Configuration Guide for the C-Series - Force10 Networks

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

This equation shows <strong>the</strong> relationship between actual sampling rate, sub-sampling rate, and<br />

<strong>the</strong> hardware sampling rate <strong>for</strong> an interface:<br />

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

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

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

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

Back-off Mechanism<br />

Back-off Mechanism is supported on plat<strong>for</strong>m e<br />

If <strong>the</strong> sampling rate <strong>for</strong> an interface is set to a very low value, <strong>the</strong> CPU can get overed with flow samples<br />

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

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

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

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

to <strong>the</strong> desired value.<br />

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

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

show sflow command.<br />

sFlow on LAG ports<br />

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

Extended sFlow<br />

Extended sFlow is supported fully on plat<strong>for</strong>m e<br />

Plat<strong>for</strong>m c only supports extended in<strong>for</strong>mation processing <strong>for</strong> switching.<br />

Extended sFlow packs additional in<strong>for</strong>mation in <strong>the</strong> sFlow datagram depending on <strong>the</strong> type of sampled<br />

packet. The following options can be enabled:<br />

• extended-switch — 802.1Q VLAN ID and 802.1p priority in<strong>for</strong>mation<br />

• extended-router — Next-hop and source and destination mask length.<br />

<strong>FTOS</strong> <strong>Configuration</strong> <strong>Guide</strong>, version 7.7.1.0 309

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