Rapid Pvst+ Port State Overview - Cisco Nexus 9000 Series Configuration Manual

Rapid PVST+
This figure shows port roles. A port with the root or a designated port role is included in the active topology.
A port with the alternate or backup port role is excluded from the active topology.
Figure 7: Sample Topology Demonstrating Port Roles

Rapid PVST+ Port State Overview

Propagation delays can occur when protocol information passes through a switched LAN. As a result, topology
changes can take place at different times and at different places in a switched network. When a Layer 2 LAN
port transitions directly from nonparticipation in the spanning tree topology to the forwarding state, it can
create temporary data loops. Ports must wait for new topology information to propagate through the switched
LAN before starting to forward frames.
Each Layer 2 LAN port on the device that uses Rapid PVST+ or MST exists in one of the following four
states:
• Blocking—The Layer 2 LAN port does not participate in frame forwarding.
• Learning—The Layer 2 LAN port prepares to participate in frame forwarding.
• Forwarding—The Layer 2 LAN port forwards frames.
• Disabled—The Layer 2 LAN port does not participate in STP and is not forwarding frames.
When you enable Rapid PVST+, every port in the device, VLAN, and network goes through the blocking
state and the transitory states of learning at power up. If properly configured, each Layer 2 LAN port stabilizes
to the forwarding or blocking state.
When the STP algorithm places a Layer 2 LAN port in the forwarding state, the following process occurs:
1 The Layer 2 LAN port is put into the blocking state while it waits for protocol information that suggests
it should go to the learning state.
Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide, Release 7.x
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Configuring Rapid PVST+ Using Cisco NX-OS