Administrator Guide

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 absence of a configured rate in the equation. That absence 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 the CPU condition is cleared. This is as per sFlow version 5 draft. After the back-off changes the
sample-rate, you 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.
You can view the actual sampling-rate of the interface and the configured sample-rate 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.
Enabling Extended sFlow
Dell Networking OS supports extended-switch information processing only.
Extended sFlow packs additional information in the sFlow datagram depending on the type of sampled
packet. You can enable the following options:
• 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.
• Enable extended sFlow.
sflow [extended-switch] [extended-router] [extended-gateway] enable
By default packing of any of the extended information in the datagram is disabled.
• Confirm that extended information packing is enabled.
show sflow
sFlow 837