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have two DC, with 2 N5K on each DC. I want to connect these pairs with Fabricpath to have full bandwidth used. I've seen that vPC back to back can do the trick. BUT Fabricpath brings vPC+ with it, and I use FEX on each site. So is it worth having Fabricpath to get the vPC+ or no and I must consider the vPC classic with FEX and vPC back to back between pairs?

Thanks,

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    – Ron Maupin ♦
    Aug 15, 2017 at 4:48

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You don't need fabricpath to run a vPC+ from a FEX. Fabricpath is really only useful in large data centers where you have a multiple tier topology (Core, Aggregation, Access). In a smaller setup using a collapsed core type design, vPC is simpler and accomplishes the same goal of getting rid of spanning tree.

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  • Minor point - STP still runs as a fail-safe in a VPC environment.
    – rnxrx
    Feb 2, 2017 at 16:25
  • You say that vPC+ doesn't need FP. But as I see on the doc, vPC+ is only mentioned with FP. I mean by vPC+ the enhancement of vPC that emulates a single switch to third party devices like FEX or servers and permits a more balanced traffic than vPC.
    – Jey10
    Feb 2, 2017 at 19:48
  • vPC emulates a single switch to another device. This allows you to have one link of a port-channel connected to switch 1 and the other link to switch 2. vPC+ refers to running vPC from a FEX. You definitely don't need fabricpath, we are running vPC+ in our environment without FP.
    – John K.
    Feb 2, 2017 at 20:02
  • I think you're talking about enhanced vPC. From the cisco doc : "The only significant differences between vPC and vPC+ are that the latter requires the configuration of a virtual switch ID and the peer link now consists of Cisco FabricPath core ports" So in vPC, each host sends always to the same vPC peer, based on its MAC. With vPC+, the emulated switch ID is used and their is a balanced traffic.
    – Jey10
    Feb 2, 2017 at 22:44
  • I'll have to search around, I'm pretty sure I read in some documentation or a book that vPC+ simply referred to a vPC connected to a Fex. Maybe they changed the terminology.
    – John K.
    Feb 3, 2017 at 13:46
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Both approaches will work and are actively documented and supported. FP starts to really have a significant advantage if you have more than the 4 switches in your design and, particularly, if you ever wanted to add more sites (3 sites would push you back to STP). FP has the advantage of less configuration and the ability to do some interesting things with anycast HSRP (again - more significant if you wanted to run more than two switches in a site) and somewhat greater flexibility. The downside is that it's not only Cisco proprietary but is limited to a smaller subset of older (and more expensive) switches - specifically 7K with F-series or M3 blades and 5500/5600.

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  • Yeah a third site a possibility so I will consider both solutions
    – Jey10
    Feb 2, 2017 at 19:45
  • If a third site is a possibility and you want to have L2 adjacencies between sites then VPC is categorically not the right way to go. FP is solid and has the advantage of working on an arbitrary topology (vs needing 4 physical links between sites) but with all else being equal I would tend to look at a pure L3 design between sites as an underlay and running some kind of L2 or L2/L3 overlay - like OTV or VXLAN-EVPN. This ends up as the best of both worlds - L3 stability, scalability and fast convergence combined with full flexibility.
    – rnxrx
    Feb 2, 2017 at 20:19

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