How to configure sFlow on Juniper EX and QFX switches

Before you begin, be aware:

• These devices support up to four Auvik collectors being connected. 
• sFlow can’t be configured on a Layer 3 VLAN-tagged interface.
• sFlow can’t be configured on a Link Aggregation Group (LAG) interface, but can be enabled on the member of a LAG.

These instructions assume:

• The date, time, and time zone are correctly set on the switch.
• You have Telnet or SSH credentials and access to the switch.
• You know the IP address of your Auvik collector.

Access the switch CLI

1. Telnet or SSH into the switch.
2. Enter privileged mode by typing enable and entering your enable password.

Configure sFlow

Run the following command. Replace <AuvikCollectorIP> with the IP address of your Auvik collector, and <AuvikPort> with one of the following port numbers: 2055, 2056, 4432, 4739, 6343, 9995, or 9996. Replace <sampleRate> with the desired sample-rate egress: 128, 256, 512, or 1024.

set protocols sflow collector <AuvikCollectorIP> udp-port <AuvikPort>
set interfaces <interface>
set polling-interval 60
set sample-rate egress <sampleRate>
  
# Example:
# set protocols sflow collector 10.204.32.46 udp-port 2055
# set sflow interfaces ge-0/0/0
# set sflow polling-interval 60
# set sflow sample-rate egress 1

Confirm the settings

Run the following command to confirm the configuration: 

show sflow collector
show sflow interface

Reference:

https://www.juniper.net/documentation/en_US/junos/topics/example/sflow-configuring-ex-series.html