What is a probable cause for dropped packets when using a FortiGate?

The reverse path forwarding (RPF) check is crucial for preventing IP address spoofing and ensuring that incoming packets are coming from a legitimate source. When RPF is enabled, the FortiGate firewall checks the source IP address of each incoming packet against the routing table. If the RPF check fails—meaning there is no valid route back to the source of the packet—FortiGate will drop the packet to maintain security and network integrity.

This is particularly important in a scenario where the firewall is intended to prevent malicious activity. If a packet has a source IP address that doesn't correspond to a legitimate route, it could be indicative of potential spoofing. Hence, RPF is proactive in maintaining secure communication across the network.

Other factors, such as an issue with the forward policy check or subnet not being present in the routing table, might also lead to dropped packets, but they typically do not represent the foundational security role that RPF plays in packet filtering and routing verification. An IP issue with a destination workstation may lead to connectivity problems but does not directly relate to the packet dropping mechanism in the same manner as RPF, making it less likely as a primary cause.