Implementing the Rapid Spanning Tree Protocol – RSTP
RSTP port states

RSTP provides rapid convergence following the failure or re-establishment of a switch, switch port, or link. An RSTP topology change will cause a transition in the appropriate switch ports to the forwarding state through either explicit handshakes or a proposal and agreement process and synchronization.

With RSTP, the role of a port is separated from the state of a port. For example, a designated port could be in the discarding state temporarily, even though its final state is to be forwarding.

The RTSP port states correspond to the three basic operations of a switch port: discarding, learning, and forwarding.

The port states have these characteristics:

  • Discarding – This state is seen in both a stable active topology and during topology synchronization and changes. The discarding state prevents the forwarding of data frames, thus "breaking" the continuity of a Layer 2 loop.
  • Learning – This state is seen in both a stable active topology and during topology synchronization and changes. The learning state accepts data frames to populate the MAC table in an effort to limit flooding of unknown unicast frames.
  • Forwarding – This state is seen only in stable active topologies. The forwarding switch ports determine the topology. Following a topology change, or during synchronization, the forwarding of data frames occurs only after a proposal and agreement process.

In all port states, a port will accept and process BPDU frames.