Port States; Rapid Pvst+ Port State Overview - Cisco Nexus 3000 series Configuration Manual

Configuring Rapid PVST+
In a stable topology with consistent port roles throughout the network, Rapid PVST+ ensures that every root
port and designated port immediately transition to the forwarding state while all alternate and backup ports
are always in the blocking state. Designated ports start in the blocking state. The port state controls the operation
of the forwarding and learning processes.
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 (see the following figure).
Figure 11: Sample Topology Demonstrating Port Roles
Related Topics
Election of the Root Bridge, on page 77

Port States

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 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 LAN port on a software using Rapid PVST+ or MST exists in one of the following four states:
• Blocking—The LAN port does not participate in frame forwarding.
• Learning—The LAN port prepares to participate in frame forwarding.
• Forwarding—The LAN port forwards frames.
Cisco Nexus 3000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.0(3)U1(1)
Understanding Rapid PVST+
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