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Example: Configuring sFlow Technology to Monitor Network Traffic on EX Series Switches


sFlow technology is a networking monitoring technology for high-speed switched or routed networks. It is a technology that is based on statistical sampling. You can configure sFlow technology to continuously monitor traffic at wire speed on all interfaces simultaneously. sFlow data can be used to provide network traffic visibility information. You can specify sampling rates for ingress and egress packets. Junos OS fully supports the sFlow standard described in RFC 3176, InMon Corporation's sFlow: A Method for Monitoring Traffic in Switched and Routed Networks.

This example describes how to configure and use sFlow technology to monitor network traffic.


This example uses the following hardware and software components:

  • One EX Series switch

  • Junos OS Release 9.3 or later for EX Series switches

Overview and Topology

sFlow technology samples network packets and sends the samples to a monitoring station. You can specify sampling rates for ingress and egress packets. The information gathered is used to create a network traffic visibility picture.

An sFlow monitoring system consists of an sFlow agent embedded in the switch and a centralized collector. The sFlow agent runs on the switch. It combines interface counters and flow samples and sends them across the network to the sFlow collector. Figure 1 depicts the basic elements of the sFlow system.

Figure 1: sFlow Technology Monitoring System
sFlow Technology Monitoring System


To configure sFlow technology, perform the following tasks:

CLI Quick Configuration

To quickly configure sFlow technology, copy the following commands and paste them into the switch terminal window:

[edit protocols]

set sflow collector udp-port 5600

set sflow interfaces ge-0/0/0

set sflow polling-interval 20

set sflow sample-rate egress 1000

Step-by-Step Procedure

To configure sFlow technology:

  1. Configure the IP address and UDP port of the collector:
    [edit protocols]

    user@switch# set sflow collector udp-port 5600

    You can configure a maximum of 4 collectors.

    The default UDP port is 6343.

  2. Enable sFlow technology on a specific interface:

    [edit protocols sflow]

    user@switch# set interfaces ge-0/0/0

    You cannot enable sFlow technology on a Layer 3 VLAN-tagged interface.

    You cannot enable sFlow technology on a link aggregation group (LAG) interface, but you can enable it on the member interfaces of a LAG.

  3. Specify in seconds how often the sFlow agent polls the interface:
    [edit protocols sflow]

    user@switch# set polling-interval 20

    The polling interval can be specified as a global parameter also. Specify 0 if you do not want to poll the interface.

  4. Specify the rate at which egress packets must be sampled:
    [edit protocols sflow]

    user@switch# set sample-rate egress 1000

    You can specify both egress and ingress sampling rates. If you set only the egress sampling rate, the ingress sampling rate will be disabled.


    We recommend that you configure the same sampling rates on all the ports on a line card. If you configure different sampling rates are different, the lowest value is used for all ports. You could still configure different rates on different line cards.


Check the results of the configuration:


To confirm that the configuration is correct, perform these tasks:

Verifying That sFlow Technology Is Configured Properly


Verify that sFlow technology is configured properly.


Use the show sflow command:

user@switch> show sflow

The sampling limit cannot be configured and is set to 300 packets/second per FPC.


The output shows that sFlow technology is enabled and specifies the values for the sampling limit, polling interval, and the egress sampling rate.

Verifying That sFlow Technology Is Enabled on the Specified Interface


Verify that sFlow technology is enabled on the specified interfaces and display the sampling parameters.


Use the show sflow interface command:

user@switch> show sflow interface


The output indicates that sFlow technology is enabled on the ge-0/0/0.0 interface with an egress sampling rate of 1000, a disabled ingress sampling rate, and a polling interval of 20 seconds.

Verifying the sFlow Collector Configuration


Verify the sFlow collector's configuration.


Use the show sflow collector command:


The output displays the IP address of the collectors and the UDP ports. It also displays the number of samples.