Interoperability With Rapid Pvst+: Understanding Pvst Simulation - Cisco nexus 5000 series Configuration Manual

Configuring Multiple Spanning Tree

Interoperability with Rapid PVST+: Understanding PVST Simulation

MST interoperates with Rapid PVST+ with no need for user configuration. The PVST simulation feature
enables this seamless interoperability.
Note PVST simulation is enabled by default. That is, by default, all interfaces on the switch interoperate between
MST and Rapid PVST+.
However, you may want to control the connection between MST and Rapid PVST+ to protect against
accidentally connecting an MST-enabled port to a Rapid PVST+-enabled port. Because Rapid PVST+ is the
default STP mode, you may encounter many Rapid PVST+-enabled connections.
Disabling Rapid PVST+ simulation, which can be done per port or globally for the entire switch, moves the
MST-enabled port to the blocking state once it detects it is connected to a Rapid PVST+-enabled port. This
port remains in the inconsistent state until the port stops receiving Rapid PVST+/SSTP BPDUs, and then the
port resumes the normal STP transition process.
Configuring MST
MST Configuration Guidelines
When configuring MST, follow these guidelines:
• When you work with private VLANs, enter the private-vlan synchronize command to map the secondary
• When you are in the MST configuration mode, the following guidelines apply:
Enabling MST
You must enable MST; Rapid PVST+ is the default.
Changing the spanning tree mode disrupts traffic because all spanning tree instances are stopped for the
Caution
previous mode and started for the new mode. Also, having two different spanning-tree modes on Virtual
Port Channel (vPC) peer switches is an inconsistency, so this operation is disruptive.
OL-25842-01
VLANs to the same MST instance as the primary VLAN.
◦ Each command reference line creates its pending regional configuration.
◦ The pending region configuration starts with the current region configuration.
◦ To leave the MST configuration mode without committing any changes, enter the abort command.
◦ To leave the MST configuration mode and commit all the changes that you made before you left
the mode, enter the exit command.
Cisco Nexus 5000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.1(3)N1(1)
Interoperability with Rapid PVST+: Understanding PVST Simulation
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