What are two modes of unicast reverse path forwarding?

Unicast reverse path forwarding (uRPF) is a mechanism used to verify the reachability of a source IP address by ensuring that incoming packets on an interface match the routing table for that source address. This process helps to prevent certain types of IP spoofing attacks.

The two modes of unicast reverse path forwarding are strict and loose. In strict mode, the incoming packet's source address must be reachable via the interface it arrives on, meaning that the router will only accept packets if the best route to the source address leads back through the same interface. This provides a high level of verification but can block legitimate traffic in certain network setups.

In loose mode, the router checks if there is any route to the source address, irrespective of the incoming interface. This means that even if the packet arrives on a different interface than the one specified by the route back to the source, the packet would still be considered valid as long as there is a route to that source address. This allows for more flexibility in accepting packets but offers less protection compared to strict mode, as it may allow some spoofed addresses that are reachable from other paths within the network.

This understanding of strict and loose modes is essential in configuring routers for security, ensuring that the necessary balance between