A stateless firewall filter can filter packets transiting the device from a source to a destination, or packets originating from, or destined for, the Routing Engine. Stateless firewall filters applied to the Routing Engine interface protect the processes and resources owned by the Routing Engine.
You can apply a stateless firewall filter to an input or output interface, or to both. Every packet, including fragmented packets, is evaluated against stateless firewall filters.