Cisco Catalyst 3750 - VLAN-Bridge Spanning Tree; Configuring Spanning-Tree Features; Default Spanning-Tree Configuration

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Catalyst 3750 Metro Switch Software Configuration Guide
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Chapter 14 Configuring STP
Configuring Spanning-Tree Features
VLAN-Bridge Spanning Tree
Cisco VLAN-bridge spanning tree is used with the fallback bridging feature (bridge groups), which
forwards non-IP protocols such as DECnet between two or more VLAN bridge domains or routed ports.
The VLAN-bridge spanning tree allows the bridge groups to form a spanning tree on top of the individual
VLAN spanning trees to prevent loops from forming if there are multiple connections among VLANs.
It also prevents the individual spanning trees from the VLANs being bridged from collapsing into a
single spanning tree.
To support VLAN-bridge spanning tree, some of the spanning-tree timers are increased. To use the
fallback bridging feature, you must have the enhanced multilayer software image installed on your
switch. For more information, see Chapter 33, “Configuring Fallback Bridging.”
Configuring Spanning-Tree Features
These sections describe how to configure spanning-tree features:
• Default Spanning-Tree Configuration, page 14-11
• Spanning-Tree Configuration Guidelines, page 14-12
• Changing the Spanning-Tree Mode, page 14-13 (required)
• Disabling Spanning Tree, page 14-14 (optional)
• Configuring the Root Switch, page 14-14 (optional)
• Configuring a Secondary Root Switch, page 14-16 (optional)
• Configuring Port Priority, page 14-17 (optional)
• Configuring Path Cost, page 14-18 (optional)
• Configuring the Switch Priority of a VLAN, page 14-19 (optional)
• Configuring Spanning-Tree Timers, page 14-20 (optional)
Default Spanning-Tree Configuration
Table 14-3 shows the default spanning-tree configuration.
Table 14-3 Default Spanning-Tree Configuration
Feature Default Setting
Enable state Enabled on VLAN 1.
For more information, see the “Supported
Spanning-Tree Instances” section on
page 14-10.
Spanning-tree mode PVST+. (Rapid PVST+ and MSTP are
disabled.)
Switch priority 32768.
Spanning-tree port priority (configurable on a per-interface basis) 128.