Cisco Catalyst 2960 Series, Configuration Manual

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Related Topics
Specifying the MST Region Configuration and Enabling MSTP , on page 261
MSTP Configuration Guidelines, on page 243
Multiple Spanning-Tree Regions, on page 245
Configuring the Root Switch , on page 264
Root Switch, on page 244
Specifying the MST Region Configuration and Enabling MSTP , on page 261
Information About MSTP
MSTP Configuration
MSTP, which uses RSTP for rapid convergence, enables multiple VLANs to be grouped into and mapped to
the same spanning-tree instance, reducing the number of spanning-tree instances needed to support a large
number of VLANs. The MSTP provides for multiple forwarding paths for data traffic, enables load balancing,
and reduces the number of spanning-tree instances required to support a large number of VLANs. It improves
the fault tolerance of the network because a failure in one instance (forwarding path) does not affect other
instances (forwarding paths).
The multiple spanning-tree (MST) implementation is based on the IEEE 802.1s standard.
Note
The most common initial deployment of MSTP is in the backbone and distribution layers of a Layer 2 switched
network. This deployment provides the highly available network required in a service-provider environment.
When the switch is in the MST mode, the RSTP, which is based on IEEE 802.1w, is automatically enabled.
The RSTP provides rapid convergence of the spanning tree through explicit handshaking that eliminates the
IEEE 802.1D forwarding delay and quickly transitions root ports and designated ports to the forwarding state.
Both MSTP and RSTP improve the spanning-tree operation and maintain backward compatibility with
equipment that is based on the (original) IEEE 802.1D spanning tree, with existing Cisco-proprietary Multiple
Instance STP (MISTP), and with existing Cisco PVST+ and rapid per-VLAN spanning-tree plus (Rapid
PVST+).
A switch stack appears as a single spanning-tree node to the rest of the network, and all stack members use
the same switch ID.
MSTP Configuration Guidelines
• When you enable MST by using the
spanning-tree mode mst
global configuration command, RSTP
is automatically enabled.
• For configuration guidelines about UplinkFast, BackboneFast, and cross-stack UplinkFast, see the
relevant sections in the Related Topics section.
• When the switch is in MST mode, it uses the long path-cost calculation method (32 bits) to compute the
path cost values. With the long path-cost calculation method, the following path cost values are supported:
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
243
Information About MSTP