To ensure proper functioning within an MST (Multiple Spanning Tree) region, the following parameters must match across all switches:
* Revision number:
* The revision number identifies the version of the MST configuration. All switches within the same MST region must have the same revision number to ensure consistency.
* MSTI-to-VLAN mapping:
* The MSTI (Multiple Spanning Tree Instance) to VLAN mapping must be identical on all switches. This mapping ensures that each VLAN is assigned to the correct spanning tree instance.
* Configuration name:
* The configuration name (or region name) must be the same across all switches. This name uniquely identifies the MST region and must be consistent to ensure switches recognize they are part of the same region.
References:
* The MSTP configuration requirements are detailed in Juniper network configuration guides and standards documents on MSTP.

VSTP has the following benefits:
Connects devices that are not part of the network
Compatible with Cisco PVST+
VSTP and RSTP are the only spanning-tree protocols that can be configured concurrently on a device.
VSTP Restrictions
VSTP has these restrictions:
The EX Series switches EX4300, EX4600 and the QFX platforms QFX5100,QFX3500,QFX3600 support 510 Vlans on VSTP.
VSTP is not supported on the SRX platform - just STP/RSTP/MSTP are supported on SRX Series.
On EX Series (except EX9200) and QFX Series switches running Junos OS that supports ELS- VSTP can support up to 510 VLANs.
On EX9200 switches-VSTP can support up to 4000 VLANs.
On an EX Series switch running Junos OS that does not support ELS-VSTP can support up to
253 VLANs.