Administrator Guide

Figure 123. sFlow Trac Monitoring System
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 specically, 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 congured on that port in the future. Back-o is triggered
based on the port-pipe’s hardware sampling rate.
For example, if port 1 in the port-pipe has sFlow congured with a 16384 sampling rate while port 2 in the port-pipe has sFlow congured
but no sampling rate set, Dell Networking OS applies a global sampling rate of 512 to port 2. The hardware sampling rate on the port-pipe is
then set at 512 because that is the lowest congured rate on the port-pipe. When a high trac situation occurs, a back-o is triggered and
the hardware sampling rate is backed-o from 512 to 1024. Note that port 1 maintains its sampling rate of 16384; port 1 is unaected
because it maintains its congured sampling rate of 16484.
To avoid the back-o, either increase the global sampling rate or congure all the line card ports with the desired sampling rate even if
some ports have no sFlow congured.
Important Points to Remember
• The Dell Networking OS implementation of the sFlow MIB supports sFlow conguration via snmpset.
• By default, sFlow collection is supported only on data ports. If you want to enable sFlow collection through management ports, use the
management egress-interface-selection and application sflow-collector commands in Conguration and EIS
modes respectively.
• sFlow sampling is done on a per-port basis.
• 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 eect. 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.
• 802.1P source priority eld is not lled in extended switch element in sFlow datagram.
sFlow
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