I haven't found anything recently that really addresses this design question. There are several good papers on implementing Anycast-RP on a pair of Nexus switches, but I haven't found anything that talks about redundancy between data centers. If a customer has a pair of Nexus switches in data center A, and a pair in data center B. Would you just use a single anycast-rp with four devices, or would you do a different anycast-rp between the Nexus switches in the same data center, and then MSDP between the Nexus switches in different data centers? Also, if you use MSDP between data centers would you use the same anycast address on all four switches, or one for data center A, and a different one for data center B, then configure all PIM routers with two RPs. Has anyone found any good design guides that I just haven't found?