Reference Guide

sFlow
sFlow is a standard-based sampling technology embedded within switches and routers which is used to monitor network traffic.
It is designed to provide traffic monitoring for high-speed networks with many switches and routers.
Topics:
• Overview
• Implementation Information
• Enabling and Disabling sFlow
• Enabling and Disabling sFlow on an Interface
• Enabling sFlow Max-Header Size Extended
• sFlow Show Commands
• Configuring Specify Collectors
• Changing the Polling Intervals
• Back-Off Mechanism
• sFlow on LAG ports
• Enabling Extended sFlow
Overview
The Dell Networking OS supports sFlow version 5.
sFlow uses two types of sampling:
● Statistical packet-based sampling of switched or routed packet flows.
● Time-based sampling of interface counters.
The sFlow monitoring system consists of an sFlow agent (embedded in the switch/router) and an sFlow collector. The sFlow
agent resides anywhere within the path of the packet and combines the flow samples and interface counters into sFlow
datagrams and forwards them to the sFlow collector at regular intervals. The datagrams consist of information on, but not
limited to, packet header, ingress and egress interfaces, sampling parameters, and interface counters.
Application-specific integrated circuits (ASICs) typically complete packet sampling. sFlow collector analyses the sFlow
datagrams received from different devices and produces a network-wide view of traffic flows.
Implementation Information
Dell Networking sFlow is designed so that the hardware sampling rate is per line card port-pipe and is decided based on all the
ports in that port-pipe.
If you do not enable sFlow on any port specifically, the global sampling rate is downloaded to that port and is to calculate the
port-pipe’s lowest sampling rate. This design supports the possibility that sFlow might be configured on that port in the future.
Back-off is triggered based on the port-pipe’s hardware sampling rate.
The default global sampling rate is 32768. The sampling rates are determined as follows:
● If the interface states are up and the sampling rate is not configured on the port, the default sampling rate is calculated
based on the line speed.
● If the interface states are shut down, the sampling rate is set using the global sampling rate.
● If the global sampling rate is non-default, for example 256, and if the sampling rate is not configured on the interface, the
sampling rate of the interface is the global non-default sampling rate, that is, 256.
To avoid the back-off, either increase the global sampling rate or configure all the line card ports with the desired sampling rate
even if some ports have no sFlow configured.
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