Mst Bpdus; Mst Configuration Information - Cisco Nexus 7000 Series Configuration Manual

Configuring MST Using Cisco NX-OS
A collection of interconnected devices that have the same MST configuration is an MST region. An MST
region is a linked group of MST bridges with the same MST configuration.
The MST configuration controls the MST region to which each device belongs. The configuration includes
the name of the region, the revision number, and the VLAN-to-MST instance assignment mapping.
A region can have one or multiple members with the same MST configuration. Each member must be capable
of processing 802.1w bridge protocol data units (BPDUs). There is no limit to the number of MST regions in
a network.
Each device can support up to 65 MST instances (MSTIs), including Instance 0, in a single MST region.
Instances are identified by any number in the range from 1 to 4094. The system reserves Instance 0 for a
special instance, which is the IST. You can assign a VLAN to only one MST instance at a time.
The MST region appears as a single bridge to adjacent MST regions and to other Rapid PVST+ regions and
802.1D spanning tree protocols.
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 12: 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
Cisco Nexus 7000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.x
MST BPDUs
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