Routing control functions (RCF) is a language that can be used to express route filtering and attribute modification logic in a powerful and programmatic fashion.

For a wide range of features such as MPLS, MPLS-over-GRE, nexthop-groups, VPN, EVPN, BGP-LU, etc, the kernel injects CPU-generated packets into the hardware pipeline as a result of fwd*/txfwd kernel interfaces being used as next-hop devices on kernel routes.

This feature gives users the ability to use Route Control Functions (RCFs) to create custom policies for deciding which routes with IP next-hops should be programmed into the kernel with fwd* next-hop devices so the associated kernel packets are inserted into the ingress pipeline of hardware forwarding instead of being software-forwarded by the kernel.

When a static route is configured with a nexthop group, by default the static route is eligible for FIB insertion