Figure 28: Mstp Regions And Legacy Rstp Lan Connection - GE T1000 Technical Manual

Chapter 4 – Functions
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Instead of calculating the spanning tree for all VLANs, MSTP allows grouping a set of
VLANs in instances, and these instances can run inside a region. Switches that are
set to run the protocol need to find their neighbors, which are also running MSTP.
This concept defines three main characteristics that allow bridges to become a
member of the same region:

MSTI configuration name;

MSTI configuration revision;

VLANs mapped to the MSTI.
It is defined that bridges are at the same region if they have the same configuration
name, revision and the same VLANs mapped.
The figure below shows an example of the MSTP instance regions.

Figure 28: MSTP regions and legacy RSTP LAN connection

Each region will have its own root switch, as it behaves as a separate spanning tree
to the others. Also, there will be a switch that will be elected as the regional root,
which will allow regions to be connected to each other. The figure below exemplifies
these bridges in regions A and B.
GE Reason Switches
REASON SWITCHES-TM-EN-3