On MX304 platforms running Junos OS, J-Flow (v5, v9) and IPFIX export cannot be configured to use the mgmt_junos interface.

All flow export traffic must be sent through a regular data-plane interface.

• Attempting to configure J-Flow/IPFIX export over mgmt_junos fails or is unsupported.
• No CLI option exists to bind flow export to the management interface.

The mgmt_junos interface is control-plane only and does not handle high-volume telemetry traffic generated by the Packet Forwarding Engine (PFE). Flow export requires a data-plane interface for proper operation.

Solution:

Configure J-Flow/IPFIX export on a front-panel data-plane interface (e.g., ge-, xe-, or et- ports).

MX304 supports inline active flow monitoring (IPFIX/v9) on front-panel ports, as documented in the MX304 Feature Guide.

There is no statement in official documentation that enables export over mgmt_junos for MX platforms.