STP - RSTP convergence process

When implementing RSTP as the Spanning Tree Protocol (STP) in a Layer 2 topology, during the RSTP proposal-agreement process, the RSTP protocol goes through several stages to achieve convergence. These steps in the convergence process are described below:

  • Proposal: The root bridge sends a proposal to its directly connected switches indicating that it has a better path to the root. The bridges then stop forwarding data frames and go into a discarding state to prevent loops.
  • Sync: The directly connected switches send a sync message to their directly connected switches to prepare them for the upcoming change in the network topology.
  • Agreement: After receiving the sync message, the directly connected switches send an agreement back to the root bridge. This indicates that they have prepared their directly connected switches for the upcoming change.
  • Forwarding: Once the root bridge receives an agreement from all its directly connected switches, it starts forwarding data frames again. The directly connected switches then repeat this process with their directly connected switches.