In a vPC configuration, both Nexus switches (N7K-1 and N7K-2) are designed to work together to present themselves as a single logical entity to downstream devices. This design allows for a loop-free topology without the need for Spanning Tree Protocol (STP) to block any of the ports to prevent loops. As a result, both N7K-1 and N7K-2 share the same STP priority, making them appear as a single STP root to the rest of the network. This approach enhances the use of available bandwidth and provides redundancy without relying on STP to resolve loops.
References := The principles of vPC and its interaction with STP are well documented in Cisco's technical literature, including the Implementing and Operating Cisco Data Center Core Technologies (DCCOR) course materials1. For a more detailed explanation, please refer to these resources.