Unicast Reverse Path Forwarding (uRPF) is a security feature used to prevent IP address spoofing by ensuring that incoming packets have a valid source address. There are two primary modes for uRPF: Strict mode and Loose mode. Strict mode requires that the source address of an incoming packet matches a specific route in the routing table and that it arrives from the expected interface. Loose mode is less stringent, simply requiring that the source address matches any route in the routing table. These modes help in enhancing network security by validating the legitimacy of packet sources.