When there are multiple, conflicting choices of a route to a particular destination, the router picks the route with the longest matching network mask. If these are still equal, the router picks the route using the following default criteria (in the order specified):
- Directly attached network interfaces
- Static routes
- ICMP redirects
- Dynamic routes
- Directly attached network interfaces that are not active.
You can also configure blackhole routes—traffic to these destinations is silently dropped.
The criteria for choosing from multiple routes with the longest matching network mask is set by choosing the relative route priorities.