980 | sFloww w w . d e l l . c o m | s u p p o r t . d e l l . c o mNote the absence of a configured rate in the equation. That is because when the hardware sampling ratevalue on the port-pipe exceeds the configured sampling rate value for an interface, the actual rate changesto the hardware rate. The sub-sampling rate never goes below a value of one.Back-off MechanismIf the sampling rate for an interface is set to a very low value, the CPU can get overloaded with flowsamples 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 backoffmechanism continues to double the sampling-rate until CPU condition is cleared. This is as per sFlowversion 5 draft. Once the back-off changes the sample-rate, users must manually change the sampling rateto the desired value.As a result of back-off, the actual sampling-rate of an interface may differ from its configured samplingrate. The actual sampling-rate of the interface and the configured sample-rate can be viewed by using theshow sflow command.sFlow on LAG portsWhen a physical port becomes a member of a LAG, it inherits the sFlow configuration from the LAG port.Extended sFlowExtended sFlow is supported fully on platform ePlatforms c and s support extended-switch information processing only.Extended sFlow packs additional information in the sFlow datagram depending on the type of sampledpacket. 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 equationshows the relationship between actual sampling rate, sub-sampling rate, and the hardware sampling ratefor an interface:Actual sampling rate = sub-sampling rate * hardware sampling rateNote: The entire AS path is not included. BGP community-list and local preference information are notincluded. These fields are assigned default values and are not interpreted by the collector.
