sFlow uses mandatory
sampling to achieve
scalability and is, for this reason, applicable to high speed networks (
gigabit per second speeds and higher). sFlow is supported by multiple network device manufacturers and
network management software vendors. An sFlow system consists of multiple devices performing two types of sampling: random sampling of
packets or
application layer operations, and time-based sampling of counters.
Flow samples Based on a defined sampling rate, an average of 1 out of n packets/operations is randomly sampled. This type of sampling does not provide a 100% accurate result, but it does provide a result with quantifiable accuracy.
Counter samples A polling interval defines how often the network device sends interface counters. sFlow counter sampling is more efficient than
SNMP polling when monitoring a large number of interfaces.
sFlow datagrams The sampled data is sent as a
UDP packet to the specified host and port. The
official port number for sFlow is port 6343. The lack of reliability in the UDP transport mechanism does not significantly affect the accuracy of the measurements obtained from an sFlow agent. If counter samples are lost then new values will be sent when the next polling interval has passed. The loss of packet flow samples results in a slight reduction of the effective sampling rate. The UDP payload contains the
sFlow datagram. Each datagram provides information about the sFlow version, the originating device’s
IP address, a sequence number, the number of samples it contains and one or more flow and/or counter samples. == sFlow versions ==