What is indicated by the presence of Reverse Path Forwarding (RPF)?

The presence of Reverse Path Forwarding (RPF) indicates that a better route exists to the source from a different interface. RPF is a mechanism used primarily in multicast routing and certain unicast scenarios, where the router checks the path that incoming packets take to ensure they arrive on the correct interface based on the known routing table.

When a router receives traffic from a source, RPF verifies whether it is arriving on the interface that is the shortest path back to that source. If the incoming interface does not match the expected interface for that route (i.e., if there is a better route available via another interface), it suggests that the path to the source is not optimal, and thus, RPF can discard the packets. This behavior prevents routing loops and ensures packets only traverse the most efficient routes.

The other answer choices don't accurately reflect the function of RPF. Traffic balancing refers to routing decisions that ensure even distribution across multiple paths, while congestion pertains to network performance detriments rather than routing efficiency. Lastly, multiple active sessions from the same source do not solely indicate RPF actions; rather, RPF is concerned with verifying the incoming interface against the best-known route to the source.