1. Set net.fibs between 2-16 in /boot/loader.conf
1. Add a route in say FIB 1 which points to a subnet (e.g. default router, or subnet behind subrouter)
2. Do a ping/traceroute to a destination with an ICMP redirect, say a subrouter behind your router, but the subrouter's "external" interface is on the same subnet but different IP as your fib 1 router IP (which also has a route to the subrouter)