Protocol Independent Multicast and Asymmetric Routing

Abstract

Originally all links in the Internet were assumed to operate bidirectionally. Like many other routing protocols, PIM (protocol independent multicast) is based on this assumption: as will be explained, PIM's concept of using the routers' unicast RIBs (routing information bases) for reverse-path-forwarding is not applicable in networks with uni-directional links. If an additional bidirectional link such as a dial-up connection exists, link-layer tunnelling can overcome these basic routing deficiencies. But in order to achieve a more efficient routing and sustain scalability we argue that multicast and unicast traffic should be distinguished either by an extended link-layer tunnelling or dual RIBs