Cisco Nexus 5000 Series Switch CLI Software Configuration Guide, NX-OS 4.0(1a)N1 (OL-16597-01, January 2009)

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9-3
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
OL-16597-01
Chapter 9 Configuring MST
Information About MST
Note We do not recommend that you partition the network into a large number of regions.
MST BPDUs
Each region has only one MST BPDU, and that BPDU carries an M-record for each MSTI within the
region (see Figure 9-1). Only the IST sends BPDUs for the MST region; all M-records are encapsulated
in that one BPDU that the IST sends (see “IST, CIST, and CST Overview” section on page 9-4 for more
information on IST). Because the MST BPDU carries information for all instances, the number of
BPDUs that need to be processed to support MSTIs is significantly reduced.
Figure 9-1 MST BPDU with M-Records for MSTIs
MST Configuration Information
The MST configuration that must be identical on all switches within a single MST region is configured
by the user.
You can configure the following three parameters of the MST configuration:
• Name—32-character string, null padded and null terminated, identifying the MST region
• Revision number—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 that the MST configuration is
committed.
• MST configuration table—4096-element table that associates each of the potential 4094 VLANs
supported to a given instance with the first (0) and last element (4095) set to 0. The value of element
number X represents the instance to which VLAN X is mapped.
Caution When you change the VLAN-to-MSTI mapping, the system restarts MST.
Protocol
information
for the IST
Protocol
information
for the MSTI
present on
the port
(M-records)
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