In last Open Networking Summit, Martin Casado from Nicira had a slide to describe the relationship between SDN and large scale physical network fabric (DCN). His main point is that SDN not obviously fits for fabric control plane, while it may be great for fabric config (OAM). His main point is that
SDN Control Plane
1. Probably have to push all state proactively
2. Multipathing requires state replication
3. Likely destination-only w/ aggregation
4. End up implementing L3 w/ extra control channel.
I buy his arguments and I think existing L3 routing protocol has solved the large scale DCN fairly well.
His slide is available at here
