Multicast in a Layer 3 VPN
So far in this book, the L3VPN discussion has focused on providing connectivity for unicast destinations. How is multicast traffic handled? To answer this question, let us first determine what the requirements are, both from the customer's and the provider's point of view. From the customer's point of view, the requirement is simple: be able to forward multicast traffic between senders and receivers in different sites using the same procedures as if they belonged to a single physical network and using private address spaces. From the provider's point of view, the goal is to satisfy the customer's requirement while maximizing his or her own profits. What this exactly means to the provider has changed over time, as L3VPN deployments have grown in both number of sites and of VPNs and as the bandwidth consumed by the multicast traffic has increased many fold. While satisfying the customer's requirement for multicast connectivity among sites, the original solution proposed for multicast VPN (mVPN) was not scalable from the provider's point of view. For this reason, a new approach to multicast support in L3VPN has been developed in the last few years in the L3VPN working group [L3VPN-WG] in the IETF.
The chapter will present both the original and the new approaches and then compare them. Basic familiarity with PIM, P2MP LSPs and unicast L3VPN concepts is assumed for the rest of this chapter. In this chapter, the terms mVPN and VPN will ...