Cisco Systems 4500 MST Instances, MST Configuration Parameters, MST Regions

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Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 18 Configuring STP and MST
About MST
MST Instances
We support 65 instances including instance 0. Each spanning tree instance is identified by an instance
ID that ranges from 0 to 4094. Instance 0 is mandatory and is always present. Rest of the instances are
optional.
MST Configuration Parameters
The MST configuration includes these three parts:
• Name—A 32-character string (null padded) that identifies the MST region.
• Revision number—An unsigned 16-bit number that identifies the revision of the current MST
configuration.
Note You must set the revision number when required as part of the MST configuration. The
revision number is not incremented automatically each time you commit the MST
configuration.
• MST configuration table—An array of 4096 bytes. Each byte, interpreted as an unsigned integer,
corresponds to a VLAN. The value is the instance number to which the VLAN is mapped. The first
byte that corresponds to VLAN 0 and the 4096th byte that corresponds to VLAN 4095 are unused
and always set to zero.
You must configure each byte manually. Use SNMP or the CLI to perform the configuration.
MST BPDUs contain the MST configuration ID and the checksum. An MST bridge accepts an MST
BPDU only if the MST BPDU configuration ID and the checksum match its own MST region
configuration ID and checksum. If either value is different, the MST BPDU is considered to be an
SST BPDU.
MST Regions
These sections describe MST regions:
• MST Region Overview, page 18-26
• Boundary Ports, page 18-27
• IST Master, page 18-27
• Edge Ports, page 18-27
• Link Type, page 18-28
MST Region Overview
Interconnected bridges that have the same MST configuration are referred to as an MST region. There
is no limit on the number of MST regions in the network.