Cisco WS-C2960-24TC-L Software Guide - Page 137
Configuring a Root Switch to Improve Convergence
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Chapter 7 Configuring Spanning Tree Configuring a Root Switch To configure a switch as the secondary root switch, perform this task in privileged mode: Task Command Configure a switch as the secondary root switch. set spantree root [secondary] vlans [dia network_diameter] [hello hello_time] 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 Command Configure a switch as the secondary root switch set spantree root [secondary] mistp-instance for an instance. instance [dia network_diameter] [hello hello_time] 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 "Configuring Spanning Tree Timers" section on page 7-44. Note Reduction of the value of the timer parameters is possible only if all of the links are LAN links of 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-Release 8.1 7-41
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