Nexus 55xx & 50×0 vPC incompatibility

A Google search doesn’t return any definitive results regarding vPC compatibility between the older Nexus 50×0 series and the newer 55xx series so I thought I’d pop up a post confirming that it indeed does NOT work. I recently ran into this issue while trying to non-disruptively swap out a 5010 switch pair with 5548s. At first, vPCs between the switches appear to only show a Type 2 inconsistency and come up. Unfortunately, at closer inspection, you’ll see that STP Bridge Assurance on the vPC peer-link will block all VLANs. This means that traffic entering one switch that needs to span the peer-link to traverse upstream will be blocked. Thus, connectivity is sporadic at best. Official word from Cisco is that vPC between the two series doesn’t work because vPC was changed in the 5500 series to allow increases in VLAN scalability, etc. At closer inspection, the documentation does note the incompatibility. Maybe the document writers can put it in one of those handy “Note: (with a pencil)” boxes in a future document release.