HP Cisco Nexus 5000 Cisco Nexus 5000 Series Switch CLI Software Configuration - Page 205

Information About Rapid PVST+ Port States 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 24: Sample Topology Demonstrating Port Roles Related Topics • Election of the Root Bridge, page 153 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. • Disabled-The LAN port does not participate in STP and is not forwarding frames. OL-16597-01 Cisco Nexus 5000 Series Switch CLI Software Configuration Guide 159