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Chapter 13 Spanning Tree Protocol
XGS-4526/4528F/4728F User’s Guide
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With MSTP, VLANs 1 and 2 are mapped to different spanning trees in the network.
Thus traffic from the two VLANs travel on different paths. The following figure
shows the network example using MSTP.
Figure 58 MSTP Network Example
13.1.5.2 MST Region
An MST region is a logical grouping of multiple network devices that appears as a
single device to the rest of the network. Each MSTP-enabled device can only
belong to one MST region. When BPDUs enter an MST region, external path cost
(of paths outside this region) is increased by one. Internal path cost (of paths
within this region) is increased by one when BPDUs traverse the region.
Devices that belong to the same MST region are configured to have the same
MSTP configuration identification settings. These include the following parameters:
• Name of the MST region
• Revision level as the unique number for the MST region
• VLAN-to-MST Instance mapping
13.1.5.3 MST Instance
An MST Instance (MSTI) is a spanning tree instance. VLANs can be configured to
run on a specific MSTI. Each created MSTI is identified by a unique number
(known as an MST ID) known internally to a region. Thus an MSTI does not span
across MST regions.
A
B
VLAN 1
VLAN 2