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Switching Configuration 69
The mechanism involves a counter that is decremented with each packet. When the counter reaches
zero a sample is taken.
5.
When a sample is taken, the counter indicating how many packets to skip before taking the next
sample is reset. The value of the counter is set to a random integer where the sequence of random
integers used over time is the Sampling Rate.
Counter Sampling
The primary objective of Counter Sampling is to efficiently, periodically export counters associated with
Data Sources. A maximum Sampling Interval is assigned to each sFlow instance associated with a Data
Source.
Counter Sampling is accomplished as follows:
• sFlow Agents keep a list of counter sources being sampled.
• When a Packet Flow Sample is generated the sFlow Agent examines the list and adds counters to the
sample datagram, least recently sampled first. Counters are only added to the datagram if the sources
are within a short period, 5 seconds say, of failing to meet the required Sampling Interval.
• Periodically, say every second, the sFlow Agent examines the list of counter sources and sends any
counters that must be sent to meet the sampling interval requirement.
The set of counters is a fixed set.
CLI Examples
The following are examples of the commands used for sFlow.
Example #1: Configure destination IP address and maxdatagram size for an sFlow receiver index
console(config)#sflow 1 destination 30.30.30.1 560
Example #2: Configure sFlow on an Ethernet interface range with a polling interval of 200 seconds
console(config)#sflow 1 polling ethernet 1/g1-1/g10 200
Example #3: Configure sFlow on an Ethernet interface with a polling interval of 400 seconds
console(config-if-1/g15)#sflow 1 polling 400