Back-Off Mechanism; Sflow On Lag Ports; Extended Sflow - Dell Force10 MXL Blade Configuration Manual

3. Configures interface Tengig 1/1 to a sub-sampling rate of 2 to achieve an actual rate of 8192.
Note: Sampling rate backoff can change the sampling rate value that is set in the hardware. The following
equation shows the relationship between the actual sampling rate, the sub-sampling rate, and the
hardware sampling rate for an interface:
Actual sampling rate = sub-sampling rate * hardware sampling rate
Note: There is an 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 is 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. 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. To view the actual sampling-rate of the interface and the configured sample-rate, use the
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

The MXL switch supports
Extended sFlow packs additional information in the sFlow datagram depending on the type of sampled
packet. You can enable the following options:
•
extended-switch
•
extended-router
•
extended-gateway
next-hop.
To enable extended sFlow, use the
command. By default, packing of any of the extended information in the datagram is disabled.
information processing only.
extended-switch
— 802.1Q VLAN ID and 802.1p priority information.
— Next-hop and source and destination mask length.
— Source and destination AS number and the border gateway protocol (BGP)
sflow [extended-switch] [extended-router] [extended-gateway] enable
show sflow
sFlow | 511