OmniSwitch OS6860/OS6900/OS10K Troubleshooting Guide Part No.032996-00 Rev.A
AOS Release 7.X and 8.X January 2015
Alcatel-Lucent Page 141 of 148
22. Troubleshooting sFlow
Summary of the commands in this chapter is listed here:
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show sflow sampler
debug sflow dump statistics
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Short for "sampled flow", sFlow is an industry standard for packet export at Layer 2. 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. The sampled packet/operation and counter information,
referred to as flow samples and counter samples respectively, are sent as sFlow datagrams to a central server
running software that analyzes and reports on network traffic; the sFlow collector. See sFlow.org consortium
for sFlow protocol specifications.
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 is a slight reduction in 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, how many samples it contains and one or more flow
and/or counter samples.
OS6900 and OS6860 allows sampling traffic at rate of 1:1 (meaning all packets are sampled):
6900> show sflow sampler
Instance Interface Receiver Rate Sample-Header-Size
----------------------------------------------------------
1 1/ 1 - 1 128
If sample rate is set to 1 and data rate is low, sFlow could get every packet, but if the data rate is high (e.g. 10G
line rate), the sample rate will not be able to keep up and sampler will auto adjust to a higher sample rate. The
configured sample rate is the lowest sample rate sFlow tries to achieve but is not guaranteed. The command
"debug sflow show rate" will show the actual rate at the time the command is executed.
sFlow is not designed to sample at a rate of 1:1. The recommended sample rates are:
10mbps = 200
100mbps = 500
1,000mbps = 1000
10,000mbps = 2000
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