IETF RFC 6754 PDF

A Protocol Independent Multicast (PIM) router uses the Reverse Path Forwarding (RPF) procedure to select an upstream interface and router in order to build forwarding state. When there are equal-cost multipaths (ECMPs), existing implementations often use hash algorithms to select a path. Such algorithms do not allow the spread of traffic among the ECMPs according to administrative metrics. This usually leads to inefficient or ineffective use of network resources. This document introduces the ECMP Redirect, a mechanism to improve the RPF procedure over ECMPs. It allows ECMP selection to be based on administratively selected metrics, such as data transmission delays, path preferences, and routing metrics.