Introduction:In normal routing i.e. In Unicast routing packet forwarding decisions are typically based on the destination address of the packet arriving at a router. The unicast routing table is organized by destination subnet and mainly set up to forward the packet toward the destination.In IP multicast routing, the router forwards the packet away from the source to make progress along the distribution tree and prevent routing loops. The router's multicast forwarding state runs more logically by organizing tables based on the reverse path, from the receiver back to the root of the distribution tree.
![Path Path](/uploads/1/2/5/4/125490362/344892166.jpg)
This process is known as reverse-path forwarding (RPF).In short, Incoming multicast packet will not be accepted/forwarded unless it is received on an interface that is the outgoing interface for unicast route to the source of the packet.Configuration Example:In below example multicast server S1 sends a multicast packet, with R1 flooding it to R2 and R3.R2 received its copy, and floods it as well. As a result R3 receives the same packet from two routers:a) On its interface fa0/0 from R1.b) On its interface s0/0 from R2.Topology Diagram:Without the RPF check, R3 would forward the packet it got from R1 to R2, and vice versa, and begin the process of looping packets also with the same logic, R1 and R2 also keep repeating the process. This duplication creates multicast routing loops and generates multicast storms that waste bandwidth and router resources.Before I dive into multicast configuration, let me share with you the initial configuration of our network.
This article includes a, related reading or, but its sources remain unclear because it lacks. Please help to this article by more precise citations. ( May 2019) Reverse-path forwarding (RPF) is a technique used in modern for the purposes of ensuring loop-free forwarding of packets in and to help prevent in routing.In standard unicast IP routing, the router forwards the packet away from the source to make progress along the distribution tree and prevent routing loops. In contrast, the router's multicast forwarding state runs more logically by organizing tables based on the reverse path, from the receiver back to the root of the distribution tree at the source of the multicast. This approach is known as reverse-path forwarding.
Each strategy is built on its predecessor – Flooding – Reverse Path Forwarding (RPF) – Reverse Path Broadcasting (RPB) – Reverse Path Multicasting (RPM). About Unicast Reverse Path Forwarding. The Unicast RPF feature helps to mitigate problems that are caused by the introduction of malformed or forged (spoofed) IP source addresses into a network by discarding IP packets that lack a verifiable IP source address. For example, a number of common types of denial-of-service (DoS) attacks, including.