I got in some lab time working with vPC+ last week. I was teaching the week-long Nexus class DCUFI in Indianapolis. I teach it about once a month via FireFly (enjoy teaching, change of scene, different activity from consulting, like the sound of own voice, get good evals, etc.). The class was sharp and a couple of folks were very interested in FabricPath and the vPC+ feature.
vPC+ is the feature whereby a pair of vPC switches at the edge of FabricPath are virtualized as a single switch in terms of the FabricPath topology, meaning that you get load-balanced behavior to the pair. There are configuration samples at the following URL’s:
- Configuring a vPC+ Switch ID
- Nexus 7000 FabricPath
- Cisco Nexus 5000 Series NX-OS FabricPath Configuration Guide
I also liked the Nexus 5000 FabricPath Operations Guide but it seems to have vanished from Cisco’s site since last week! I hope it is just temporarily AWOL.
Due to an upcoming migration, the site wants to run vPC on core/aggregation Nexus 7000’s supporting the old pairs of 6500 switches in the datacenters, and be ready to run FabricPath to Nexus 5500s as future pairs of Nexus 5500s are rolled out. Saying that differently, the idea was to start with FabricPath solely between the spine N7K’s, then grow the FabricPath cloud “down” to N5K’s using the newly added FabricPath feature for connectivity. Thus the initial topology would be running FabricPath solely on the vPC peer-link between the N7K’s. Doing that at the time of initial N7K rollout would minimize subsequent disruptive changes (or so we conjectured).
We tried this, it doesn’t seem to work. Watching debug, you get a lot of churn on the vPC peer-link, but it ends up with the vPC peer-link being down. The problem is ultimately that ISIS cannot come up with a link ID (LID) for the peer-link. My conjecture is that this is due to there being outside the design range contemplated or tested by Cisco, i.e. there is no other FabricPath network present. The next step I suggested would have been to restructure with a separate link other than the vPC peer-link running FabricPath, but we ran out of time and energy (and had no flexibility to recable the remote lab). We didn’t find (or perhaps recognize) any comment one way or the other about this in the documentation.
We did learn some things along the way, one of which I’d like to pass along since it might save you some frustration. We had some real problems getting the vPC peer-link to stay up initially, and kept getting an error message about switch id: for vPC+ you put the virtual switch switch-ID into the vpc domain block of the configuration. The somewhat cryptic comment in TFM (The Fine Manual) was that vPC and vPC+ cannot co-exist in the same VDC. What we saw was that some fabricpath state was persisting somewhere, even though we had removed all the fabricpath commands.
Eventually we figured out the it lurked in the vPC domain block. So if you set up a working vPC and then want to convert it to vPC+, you have to configure “no vpc domain” and then re-create the domain. That gets rid of vPC mode so you can configure vPC+. What’s in the examples and configuration guides works fine as long as you do it from scratch — just not if your peer-link is already up and running. This is something the manual could have been a lot clearer about. Anyway, hope this helps you when the time comes for you to vPC+.