In a network where Switch-1 runs STP and Switch-2 runs RSTP, what is true?

In a scenario where one switch is running the Spanning Tree Protocol (STP) and the other is running Rapid Spanning Tree Protocol (RSTP), the communication between the two will occur using STP. This is because when a switch that supports RSTP interfaces with a switch that only supports STP, it will revert to STP to ensure compatibility.

The decision for this behavior is based on how RSTP is designed to maintain backward compatibility. RSTP can recognize STP and will handle the communication appropriately so that both switches can work together within the same network. Therefore, despite the enhanced features of RSTP like faster convergence times, the presence of the STP-only switch limits the entire segment's operation to do so based on STP standards.

RSTP effectively enters a mode where it mimics STP's functionality, allowing the connected devices to maintain a loop-free topology without disruption, facilitating communication between them under the STP protocol. This ensures network stability while transitioning towards RSTP capabilities in a mixed environment.