Rapid Pvst - Cisco Nexus 9000 Series Configuration Manual

Configuring Rapid PVST+ Using Cisco NX-OS

Rapid PVST+

Rapid PVST+ is the default spanning tree mode for the software and is enabled by default on the default
VLAN and all newly created VLANs.
A single instance, or topology, of RSTP runs on each configured VLAN, and each Rapid PVST+ instance on
a VLAN has a single root device. You can enable and disable STP on a per-VLAN basis when you are running
Rapid PVST+.
Overview of Rapid PVST+
Rapid PVST+ is the IEEE 802.1w (RSTP) standard implemented per VLAN. A single instance of STP runs
on each configured VLAN (if you do not manually disable STP). Each Rapid PVST+ instance on a VLAN
has a single root switch. You can enable and disable STP on a per-VLAN basis when you are running Rapid
PVST+.
Rapid PVST+ is the default STP mode for the device.
Note
Rapid PVST+ uses point-to-point wiring to provide rapid convergence of the spanning tree. The spanning tree
reconfiguration can occur in less than 1 second with Rapid PVST+ (in contrast to 50 seconds with the default
settings in the 802.1D STP). The device automatically checks the PVID.
Rapid PVST+ supports one STP instance for each VLAN.
Note
Using Rapid PVST+, STP convergence occurs rapidly. By default, each designated port in the STP sends out
a BPDU every 2 seconds. On a designated port in the topology, if hello messages are missed three consecutive
times, or if the maximum age expires, the port immediately flushes all protocol information in the table. A
port considers that it loses connectivity to its direct neighbor designated port if it misses three BPDUs or if
the maximum age expires. This rapid aging of the protocol information allows quick failure detection.
Rapid PVST+ provides for rapid recovery of connectivity following the failure of a device, a device port, or
a LAN. It provides rapid convergence for edge ports, new root ports, and ports connected through point-to-point
links as follows:
• Edge ports—When you configure a port as an edge port on an RSTP device, the edge port immediately
Enter the spanning-tree port type interface configuration command to configure a port as an STP edge port.
We recommend that you configure all ports connected to a Layer 2 host as edge ports.
Note
• Root port—If Rapid PVST+ selects a new root port, it blocks the old root port and immediately transitions
transitions to the forwarding state. (This immediate transition was previously a Cisco-proprietary feature
named PortFast.) You should only configure ports that connect to a single end station as edge ports.
Edge ports do not generate topology changes when the link changes.
the new root port to the forwarding state.
Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide, Release 7.x
Rapid PVST+
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