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.