Administrator Guide
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sFlow
Conguring sFlow is supported on the MXL switch platform.
Overview
The Dell Networking operating system (OS) supports sFlow version 5.
sFlow is a standard-based sampling technology embedded within switches and routers which is used to monitor network trac. It is
designed to provide trac monitoring for high-speed networks with many switches and routers. sFlow uses two types of sampling:
• Statistical packet-based sampling of switched or routed packet ows.
• 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 ow 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-specic integrated circuits (ASICs) typically complete packet sampling. sFlow collector analyses the sFlow datagrams
received from dierent devices and produces a network-wide view of trac ows.
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 specically, 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 congured on that port in the future. Back-o 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 stats are up and the sampling rate is not congured on the port, the default sampling rate is calculated based on
the line speed.
• If the interface states are shutdown, the sampling rate is set using the global sampling rate.
• If the global sample rate is non-default, for example 256 bytes, and if the sampling rate is not congured on an interface, the
sampling rate of the interface is the global non-default sampling rate, that is 256 bytes.
To avoid the back-o, either increase the global sampling rate or congure all the line card ports with the desired sampling rate even
if some ports have no sFlow congured.
Important Points to Remember
• The Dell Networking OS implementation of the sFlow MIB supports sFlow conguration using the snmpset command.
• The Dell Networking OS exports all sFlow packets to the collector. A small sampling rate can equate to many exported packets. A
backo mechanism is automatically applied to reduce this amount. Some sampled packets may be dropped when the exported
packet rate is high and the backo mechanism is about to or is starting to take eect. The dropEvent counter, in the sFlow
packet, is always zero.
• Community list and local preference elds are not lled in extended gateway element in the sFlow datagram.
sFlow
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