Here is a minimal configuration for Juniper MX Netflow/J-Flow

The setup

• Trisul Network Analytics is installed on IP 10.10.100.100
• The router IP is 20.20.200.200
• We want to enable IPFIX , alternately you can use Netflow-v9
• Sample rate is 1024
• Enable ingress/egress netflow on ge-0/0/0

FPC(Flexible PIC Concentrator) is a part of the packet forwarding engine. Previously you needed a dedicated MS-MIC or MS-PIC cards.

set chassis fpc 0 sampling-instance trisul_sampling

Create a sampler named trisul_sampling and set it to 1024, add the flow server IP

set forwarding-options sampling instance trisul_sampling input rate 1024
set forwarding-options sampling instance trisul_sampling family inet output flow-server 10.10.100.100 port 2055
set forwarding-options sampling instance trisul_sampling family inet output flow-server 10.10.100.100 version-ipfix template trisul_template 
set forwarding-options sampling instance trisul_sampling family inet output inline-jflow source-address 20.20.200.200

Name of template is trisul_template, specify timeouts and IPv4 IPv6 here

set services flow-monitoring version-ipfix template trisul_template flow-active-timeout 300
set services flow-monitoring version-ipfix template trisul_template flow-inactive-timeout 60
set services flow-monitoring version-ipfix template trisul_template template-refresh-rate seconds 60
set services flow-monitoring version-ipfix template trisul_template option-refresh-rate seconds 120
set services flow-monitoring version-ipfix template trisul_template ipv4-template

This samples directly on interface

set interfaces ge-0/0/0 unit 0 family inet sampling input
set interfaces ge-0/0/0 unit 0 family inet sampling output

Active Monitoring - Juniper Docs

MX 204 Configuration Template

Setup Inline JFlow on Juniper MX