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980 | sFlow
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Note the absence of a configured rate in the equation. That is because when the hardware sampling rate
value on the port-pipe exceeds the configured sampling rate value for an interface, the actual rate changes
to the hardware rate. The sub-sampling rate never goes below a value of one.
Back-off Mechanism
If the sampling rate for an interface is set to a very low value, the CPU can get overloaded with flow
samples under high-traffic conditions. In such a scenario, a binary back-off mechanism gets triggered,
which doubles the sampling-rate (halves the number of samples per second) for all interfaces. The backoff
mechanism continues to double the sampling-rate until CPU condition is cleared. This is as per sFlow
version 5 draft. Once the back-off changes the sample-rate, users must manually change the sampling rate
to the desired value.
As a result of back-off, the actual sampling-rate of an interface may differ from its configured sampling
rate. The actual sampling-rate of the interface and the configured sample-rate can be viewed by using the
show sflow command.
sFlow on LAG ports
When a physical port becomes a member of a LAG, it inherits the sFlow configuration from the LAG port.
Extended sFlow
Extended sFlow is supported fully on platform e
Platforms
c and s support extended-switch information processing only.
Extended sFlow packs additional information in the sFlow datagram depending on the type of sampled
packet. The following options can be enabled:
•
extended-switch — 802.1Q VLAN ID and 802.1p priority information
•
extended-router — Next-hop and source and destination mask length.
•
extended-gateway — Source and destination AS number and the BGP next-hop.
Note: Sampling rate backoff can change the sampling rate value that is set in the hardware. This equation
shows the relationship between actual sampling rate, sub-sampling rate, and the hardware sampling rate
for an interface:
Actual sampling rate = sub-sampling rate * hardware sampling rate
Note: The entire AS path is not included. BGP community-list and local preference information are not
included. These fields are assigned default values and are not interpreted by the collector.