Configuring Mst; Information About Mst; Mst Overview; Mst Regions - Cisco N5010P-N2K-BE Software Configuration Manual

Information About MST

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MST Overview

You must enable MST; Rapid PVST+ is the default spanning tree mode.
Note
MST maps multiple VLANs into a spanning tree instance, with each instance having a spanning tree
topology independent of other spanning tree instances. This architecture provides multiple forwarding
paths for data traffic, enables load balancing, and reduces the number of STP instances required to
support a large number of VLANs. MST improves the fault tolerance of the network because a failure in
one instance (forwarding path) does not affect other instances (forwarding paths).
MST provides rapid convergence through explicit handshaking as each MST instance uses the IEEE
802.1w standard, which eliminates the 802.1D forwarding delay and quickly transitions root bridge ports
and designated ports to the forwarding state. (See
information on the explicit handshake agreement.)
MAC address reduction is always enabled while you are using MST. (See
PVST+"
MST improves spanning tree operation and maintains backward compatibility with these STP versions:
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MST Regions

To allow switches to participate in MST instances, you must consistently configure the switches with the
same MST configuration information (see
A collection of interconnected switches 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 switch belongs. The configuration
includes the name of the region, the revision number, and the MST VLAN-to-instance assignment map.
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 region can support up to 65 MST instances (MSTIs). 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. (See
more information on the IST.)
The MST region appears as a single bridge to adjacent MST regions and to other Rapid PVST+ regions
and 802.1D spanning tree protocols.
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
9-2
Interoperability with Rapid PVST+: Understanding PVST Simulation, page 9-9
for complete information on MAC address reduction.) You cannot disable this feature.
Original 802.1D spanning tree
Rapid per-VLAN spanning tree (Rapid PVST+)
IEEE 802.1w defined the Rapid Spanning Tree Protocol (RSTP) and was incorporated into
IEEE 802.1D.
IEEE 802.1s defined MST and was incorporated into IEEE 802.1Q.
Chapter 8, "Configuring Rapid PVST+"
"MST Configuration Information" section on page
"IST, CIST, and CST" section on page 9-4
Chapter 9

Configuring MST

for complete
Chapter 8, "Configuring Rapid
9-3).
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