Well, there's not much to say about Instant Access except the concept of the "relationship" between the Nexus 5K/6K and Nexus 2K is much the same with Instant Accept but with added PoE & stacking. And that's Instant Access in a nutshell.
6807/6880 & 6840 controls and configure the downstream 6880IA and 3560CX switches. The 6807/6880 & 6840 acts like a full-blown collapsed network where the core, distro and access layer switches can be in one chassis (not talking about VSS). It can be a single layer (core, distro & access layer in one "logical" unit) or double layer.
Geographic separation no longer applies either because, like Nexus 2K switches, fibre optics can span long distances and the downstream 6880IA and 3560CX switches can be kilometres away from the "mothership", i. e. 6807/6880 & 6840.
Particularly with current network spending trends, some companies simple don't have endless cash to spend &/or upgrade their network gear. Three-tier model will still work. Two-tier model is still applicable. Some companies are willing to experiment on a single-tier model just to keep their costs down. Win for everyone, including Cisco, and a potential re-write in Networking 101 books all over.
Cisco Instant Access
