Re: how to understanding mpls forwarding under protocols mpls

You would use this function if you have RSVP and LDP signaled LSP on your MPLS network.  These install the routes for the LSP for protocols other than BGP and use them only for the LSP traffic and not the general routing decisions in inet.0

https://www.juniper.net/documentation/en_US/junos/topics/usage-guidelines/mpls-configuring-traffic-engineering-for-lsps.html