Cisco Catalyst 4500 Series - About MST-To-PVST+ Interoperability (PVST+ Simulation)

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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 23 Configuring STP and MST
About MST-to-PVST+ Interoperability (PVST+ Simulation)
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 00d0.00b8.1400
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Interface Role Sts Cost Prio.Nbr Status
---------------- ---- --- --------- -------- --------------------------------
Fa4/4 Back BLK 1000 240.196 P2p
Fa4/5 Desg FWD 200000 128.197 P2p
Switch# show spanning-tree summary
Root bridge for:MST01
EtherChannel misconfiguration guard is enabled
Extended system ID is enabled
Portfast is disabled by default
PortFast BPDU Guard is disabled by default
Portfast BPDU Filter is disabled by default
Loopguard is disabled by default
UplinkFast is disabled
BackboneFast is disabled
Pathcost method used is long
Name Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
MST00 1 0 0 2 3
MST01 1 0 0 2 3
---------------------- -------- --------- -------- ---------- ----------
2 msts 2 0 0 4 6
Switch#
About MST-to-PVST+ Interoperability (PVST+ Simulation)
The PVST+ simulation feature enables seamless interoperability between MST and Rapid PVST+. You
can enable or disable this per port, or globally. PVST+ simulation is enabled by default.
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 this feature causes the switch to stop the MST region from interacting with PVST+ regions.
The MST-enabled port moves to a PVST peer inconsistent (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
Shared Spanning Tree Protocol (SSTP) BPDUs, and then the port resumes the normal STP transition
process.
You can for instance, disable PVST+ simulation, to prevent an incorrectly configured switch from
connecting to a network where the STP mode is not MSTP (the default mode is PVST+).
Observe these guidelines when you configure MST switches (in the same region) to interact with PVST+
switches:
• Configure the root for all VLANs inside the MST region as shown in this example:
Switch# show spanning-tree mst interface gigabitethernet 1/1
GigabitEthernet1/1 of MST00 is root forwarding
Edge port: no (trunk) port guard : none (default)
Link type: point-to-point (auto) bpdu filter: disable (default)
Boundary : boundary (PVST) bpdu guard : disable (default)
Bpdus sent 10, received 310