vPC+ Clarification

Hello all,

I'm having some issues understanding the motivation behind vPC+, and thought I'd ask you all here. I've been studying for my CCIE-DC for over a year now, and I believe I have a solid understanding of both vPC and FabricPath. I've recently been reading the Data Center Virtualization Fundamentals book by Cisco, and the section on vPC+ shows a data center design evolution. This evolution shows the design going from a 7K-5K double-sided vPC with a vPC attached host to the 5Ks, to a FabricPath topology. In the FabricPath topology, the 5Ks become vPC+ peers. I have added a link below to an image I drew on my whiteboard that shows something similar.

So my question is this. In the example above and my image linked below, what are the motivations for making the 5Ks vPC+? I understand that spine to leaf traffic will only have one switch ID (the emulated switch ID) to point to instead of two, but is that really such a big concern? In my image linked below, I have two hosts. Would not using a vPC+ topology change the behavior vs. using vPC+ if these hosts were to communicate with each other?

In the Cisco documentation I've linked to below, it states the following: "Overall, with vPC+ most of the communications between devices that
connect to the vPC+ peers is kept local and doesn't involve the spines.
This is true for both vPC connected devices and for orphan ports as
well. Orphan ports in vPC+ can communicate over the peer-link as if this
link were a regular FabricPath link". That statement doesn't make sense to me, because it implies the same wouldn't be true for a standard vPC design. A MAC address of an orphan port would be learned across the peer link assuming it's part of a vPC VLAN, and each vPC peer would have a vPC to each downstream device. So what do they mean by that?

Apologies for the length. I've been scratching my head over this for a few days now, so I'm turning to INE's community to help me get a handle on it. I believe I understand the technicalities of vPC+, but I don't understand the "why" of it all.

 

Thanks very much,

Matt

 

 

https://www.dropbox.com/s/9bz7mt34el1jc88/FabricPath.jpg?dl=0

http://www.cisco.com/c/en/us/products/collateral/switches/nexus-5000-series-switches/guide_c07-690079.html#wp9000456

 

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