Configuring A Root Switch To Improve Convergence - Cisco WS-C2948G-GE-TX Configuration Manual

Chapter 7 Configuring Spanning Tree
To configure a switch as the secondary root switch, perform this task in privileged mode:
Task
Configure a switch as the secondary root switch.
This example shows how to configure the secondary root switch for VLANs 22 and 24:
Console> (enable) set spantree root secondary 22,24 dia 5 hello 1
VLANs 22,24 bridge priority set to 16384.
VLANs 22,24 bridge max aging time set to 10 seconds.
VLANs 22,24 bridge hello time set to 1 second.
VLANs 22,24 bridge forward delay set to 7 seconds.
Console> (enable)
To configure a switch as the secondary root switch for an instance, perform this task in privileged mode:
Task
Configure a switch as the secondary root switch
for an instance.
This example shows how to set the secondary root for an instance:
Console> (enable) set spantree root secondary mistp-instance 2-4 dia 4
Instances 2-4 bridge priority set to 8192
VLInstances 2-4 bridge max aging time set to 14 seconds.
Instances 2-4 bridge hello time set to 2 seconds.
Instances 2-4 bridge forward delay set to 9 seconds.
Switch is now the root switch for active Instances 1-6.
Console> (enable)

Configuring a Root Switch to Improve Convergence

You can configure the root switch to speed up STP convergence time by reducing the value of the Hello
Time, Forward Delay Timer, and Maximum Age Timer parameters. For more information, see the
"Configuring Spanning Tree Timers" section on page
Reducing the timer parameters is possible only if your network has LAN links of 10 Mbps or faster. In
Note
a network with links of 10 Mbps or faster, the network diameter can reach the maximum value of 7. With
WAN connections, you cannot reduce the parameters.
When a link failure occurs in a bridged network, network reconfiguration is not immediate.
Reconfiguring the default parameters (that are specified by IEEE 802.1D) for the Hello Time, Forward
Delay Timer, and Maximum Age Timer requires a 50-second delay. This reconfiguration delay depends
on the network diameter, which is the maximum number of bridges between any two end stations.
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2948G-GE-TX, and Catalyst 2980G Switches Software Configuration Guide—Release 8.2GLX
78-15908-01
Command
set spantree root [secondary] vlans [dia
network_diameter] [hello hello_time]
Command
set spantree root [secondary] mistp-instance
instance [dia network_diameter] [hello hello_time]
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Configuring a Root Switch
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