Unicast RPF Behavior with a Default Route

If you configure a default route that uses an interface configured with unicast RPF, unicast RPF behaves as follows:

• Strict mode—The packet is accepted when either of the following is true:

• The source address of the packet matches any of the routes (either default or learned) that can be originated from the interface. Note that routes can have multiple destinations associated with them; therefore, if one of the destinations matches the incoming interface of the packet, the packet is accepted.
• The source address of the packet does not match any of the routes.

The packet is not accepted when either of the following is true:

• The source address of the packet matches a prefix in the routing table.
• The interface does not expect to receive a packet with this source address prefix.

• Loose mode—All packets are automatically accepted. For this reason, we recommend that you not configure unicast RPF loose mode on interfaces that the default route uses.