We are having an issue with two CS500 arrays. Both are currently connected to a Cisco UCS via the Core. Controller A is fine and up, however Controller B is not able to see the matching port on Controller A. This means that health checks fail, and no failover is possible. Investigations turned up that the ARP/MAC is failing to show up on the Core MAC table. When we hook to the FEX, same result (as expected). Our connections have been validated where A/1 is plugged into the same network as B1 and on it's own VLAN, and the same for A2/B2. Trunking is not an issue. We duplicated this issue with another CS500 we have that is being installed. Nimble support verified that ARP requests are failing between the controllers. Does anyone have any experience with Nexus and Nimble that could shed some light? Also, we have seen that the controllers can plug into the Fabric Interconnects, however our current routing prevents this.