Users Guide

580 Monitoring Switch Traffic
• When a sample is taken, the counter indicating how many packets to skip
before taking the next sample is reset. The value of the counter is set to a
random integer where the sequence of random integers used over time is
the Sampling Rate.
Counter Sampling
The primary objective of Counter Sampling is to efficiently, periodically
export counters associated with Data Sources. A maximum Sampling Interval
is assigned to each sFlow instance associated with a Data Source.
Counter Sampling is accomplished as follows:
• sFlow Agents keep a list of counter sources being sampled.
• When a Packet Flow Sample is generated the sFlow Agent examines the
list and adds counters to the sample datagram, least recently sampled first.
Counters are only added to the datagram if the sources are within a short
period, 5 seconds say, of failing to meet the required Sampling Interval.
• Periodically, say every second, the sFlow Agent examines the list of counter
sources and sends any counters that must be sent to meet the sampling
interval requirement.
The set of counters is a fixed set.
What is RMON?
Like sFlow, RMON is a technology that enables the collection and analysis of
a variety of data about network traffic. Dell EMC Networking N-Series switch
software includes an RMON probe (also known as an RMON agent) that
collect information and analyze packets. The data that is collected is defined
in the RMON MIB, RFC 2819.
RMON is defined in an Internet Engineering Task Force (IETF) specification
and is an extension of the SNMP MIB. The RMON information can be
viewed locally on the switch or by using a generic RMON console on a
network management station (NMS). SNMP does not need to be configured
on the switch to view the RMON data locally. However, if you use a
management station to view the RMON data that the switch collects and
analyzes, you must configure the following SNMP settings:
• Set up the SNMP community string to be used by the SNMP manager at a
given IP address.