Configuring A Root Switch To Improve Convergence - Cisco WS-C2950SX-48-SI 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. To do so, you must reduce the
value of the Hello Time, Forward Delay Timer, and Maximum Age Timer parameters. For information
on configuring these timers, see the
Reduction of the value of the timer parameters is possible only if all of the links are LAN links of
Note
10 Mbps or faster. In this case, the network diameter can reach the maximum value of 7. With WAN
connections, it is not possible to reduce the parameters.
When a link failure occurs in a bridged network, network reconfiguration is not immediate.
Reconfiguration requires 50 seconds, with the default parameters (specified by IEEE 802.1D) for the
Hello Time, Forward Delay Timer, and Maximum Age Timer. The reconfiguration delay depends on the
network diameter, which is the maximum number of bridges between any two points of attachment of
end stations.
78-15486-01
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide
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]
"Configuring Spanning Tree Timers" section on page
Configuring a Root Switch
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Release 8.1
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