Mst Bpdus - Cisco Nexus 9000 Series Configuration Manual

Configuring MST Using Cisco NX-OS
We do not recommend that you partition the network into a large number of regions.
Note

MST BPDUs

Each device has only one MST BPDU per interface, and that BPDU carries an M-record for each MSTI on
the device. Only the IST sends BPDUs for the MST region; all M-records are encapsulated in that one BPDU
that the IST sends. Because the MST BPDU carries information for all instances, the number of BPDUs that
need to be processed to support MST is significantly reduced compared with Rapid PVST+.
Figure 10: MST BPDU with M-Records for MSTIs
MST Configuration Information
The MST configuration that must be identical on all devices within a single MST region is configured by the
user.
You can configure the three parameters of the MST configuration as follows:
• 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
You must set the revision number when required as part of the MST configuration. The revision number
Note
is not incremented automatically each time that the MST configuration is committed.
• VLAN-to-MST instance mapping—4096-element table that associates each of the potential VLANs
Note When you change the VLAN-to-MSTI mapping, the system reconverges MST.
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.
Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide, Release 7.x
MST BPDUs
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