If port-mirrored packets are to be distributed to multiple monitoring or collection interfaces based on patterns in packet headers, it is helpful to configure a filter-based forwarding (FBF) filter on the port-mirroring egress interface.
When an FBF filter is installed as an output filter, a packet that is forwarded to the filter has already undergone at least one route lookup. After the packet is classified at the egress interface by the FBF filter, it is redirected to another routing table for additional route lookup. Obviously, the route lookup in the latter routing table (designated by an FBF routing instance) must result in a different next hop from those from the previous tables the packet has passed through, to avoid packet looping inside the Packet Forwarding Engine.
For more information about FBF configuration, see the JUNOS Routing Protocols Configuration Guide. For an example of FBF applied to an output interface, see Examples: Configuring Port Mirroring.