Reverse Path Forwarding

From Claude with some prompting
The image explains the two main modes of Reverse Path Forwarding (RPF): Strict RPF and Loose RPF.

At the top left, three hosts are sending packets to a router. The router is determining which port to use for forwarding based on the source IP address during the routing process.

The top right explains the operation of Strict RPF. In Strict RPF, all packets are validated. It compares the port used for routing the source IP with the actual receiving port, and allows the packet only if they match.

The note under Strict RPF mentions that it prevents “No Looping (primarily for multicast)” and “No Spoofing (primarily for unicast)”. Both Strict RPF and Loose RPF can help prevent looping and spoofing to some extent.

No Looping is primarily important for multicast routing. RPF is used in multicast protocols to prevent packet loops. Both Strict RPF and Loose RPF aid in loop prevention.

No Spoofing is primarily related to security issues with unicast IP traffic. IP spoofing involves an attacker using a forged source IP address to launch network attacks. Both Strict RPF and Loose RPF are effective in mitigating IP spoofing attacks.

The bottom right explains Loose RPF. In Loose RPF, an RPF interface list for the source address is configured for each port. If the receiving port is in the RPF list for that source IP, the packet is allowed.

Therefore, while Strict RPF provides more comprehensive packet checking, Loose RPF can also help prevent looping (mainly in multicast) and spoofing (mainly in unicast) by referring to the pre-configured RPF interface lists for each port and source address.