This article describes how the fxp0 interface is used.

Provides information on the fxp0 interface to be used for traffic forwarding.

The fxp0 interface on Juniper routers is expressly designed to be an 'out-of-band' management port for your router. It is not designed to support or be configured with advanced features that many other Juniper PIC's are designed for. 

While you can configure static and dynamic routing protocols that will use this interface based on the interface configuration and route lookups, any configuration that is not part of out-of-band management (Telnet/SSH for configuration, FTP to/from the router, SNMP/CFLOWD/monitoring devices, etc) is NOT supported by Juniper and should not be used.

Juniper recommends when using any IGP configuration 'interfaces all' to disable the fxp0 interface, to ensure that it will not be used for routing lookups.