Multiple Spanning Tree Protocol; Restrictions For Configuring Mstp; How To Configure Mst Protocol - Cisco ASR 900 Series Configuration Manual

Multiple Spanning Tree Protocol

The Multiple Spanning Tree Protocol (MSTP) is an STP variant that allows multiple and independent spanning
trees to be created over the same physical network. The parameters for each spanning tree can be configured
separately, so as to cause a different network devices to be selected as the root bridge or different paths to
be selected to form the loop-free topology. Consequently, a given physical interface can be blocked for some
of the spanning trees and unblocked for others.
Having set up multiple spanning trees, the set of VLANs in use can be partitioned among them; for example,
VLANs 1 - 100 can be assigned to spanning tree 1, VLANs 101 - 200 can be assigned to spanning tree 2,
VLANs 201 - 300 can be assigned to spanning tree 3, and so on. Since each spanning tree has a different
active topology with different active links, this has the effect of dividing the data traffic among the available
redundant links based on the VLAN - a form of load balancing.
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Restrictions for configuring MSTP

• RSTP is not supported. To support RSTP, all vlans are mapped to MSTI 0 when no instance is created
• PVSTP is not supported.
• Supports only 16 instances.
• Untagged EVCs do not participate in MST loop detection.

How to Configure MST Protocol

This section describes the procedure for configuring MSTP:
Restrictions for configuring MSTP, page 69
How to Configure MST Protocol, page 69
for MSTP.
LAN Switching Configuration Guide Cisco IOS XE Everest 16.5.1 (Cisco ASR 900 Series)
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