Administrator Guide

Changing the Polling Intervals
The sflow polling-interval command configures the polling interval for an interface in the maximum number of seconds between
successive samples of counters sent to the collector.
This command changes the global default counter polling (20 seconds) interval. You can configure an interface to use a different polling
interval.
To configure the polling intervals globally (in CONFIGURATION mode) or by interface (in INTERFACE mode), use the following command.
• Change the global default counter polling interval.
CONFIGURATION mode or INTERFACE mode
sflow polling-interval interval value
• interval value: in seconds.
The range is from 15 to 86400 seconds.
The default is 20 seconds.
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
Extended sFlow packs additional information in the sFlow datagram depend on the type of sampled packet. The platform 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.
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.
• 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
The bold line shows that extended sFlow settings are enabled on all three types.
DellEMC#show sflow
sFlow services are enabled
Egress Management Interface sFlow services are disabled
Global default sampling rate: 32768
Global default counter polling interval: 20
Global default extended maximum header size: 128 bytes
Global extended information enabled: none
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sFlow