Connecting the WAN

We have so far concentrated on scenarios with local-area connectivity. You might wonder whether it is possible to run multicast across a public WAN? Yes, it is. The manner in which you do so depends greatly on the services offered by your local providers.

If the provider has an mVPN service, you can connect your core devices across it. Figure 9-16 shows two deployment models. The top one connects a native PIM network over a wide-area mVPN service. The bottom one runs an enterprise mVPN network over a service provider mVPN service. In the second scenario, the mVPN service connects enterprise mVPN P devices that run native PIM. The service provider network does not have visibility of the enterprise MDTs, MTI, and other mVPN components.

Figure 9-16. mVPN Service

It is more likelyat least at the time of this writingthat multicast traffic will need to be tunneled across the WAN. Figure 9-17 shows this simpler scenario. The WAN edge routers have a LAN-facing MTI interface for MDT connectivity, a WAN-facing (regular) GRE interface, and run VRF-aware PIM. In mVPN terms, the CE-PE interface is a GRE tunnel that connects each site. This scenario allows for virtualized core networks to connect to nonvirtualized sites that run native PIM.

Figure 9-17. Single-Domain-per-Branch Site

If the remote site is also virtualized, mVPN runs on all sites, as shown in Figure 9-18. The WAN edge routers use a different GRE tunnel for each virtual network. The remote site in Figure 9-18 uses hop-by-hop tunnels, or simply VLANs, to carry multicast traffic.

Figure 9-18. Multiple-Domains-per-Branch Site

The final scenario, in Figure 9-19, shows each site as a different mVPN domain, where the CE of one domain is the PE of another. The tunnels are regular GRE and transport native multicast traffic across the WAN.

Figure 9-19. Multiple-Domains-per-Branch Site

Note

In all cases, remember that RPF requires a unicast route to the multicast source (or RP). Routers in each site must have appropriate unicast routing information in every VRF; otherwise, multicast packets will be dropped.