Cisco 2950 Software Configuration Guide - Page 310
Configuring a Secondary Root Switch
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Configuring Spanning-Tree Features Chapter 14 Configuring STP Beginning in privileged EXEC mode, follow these steps to configure a switch to become the root for the specified VLAN. This procedure is optional. Step 1 Step 2 Command configure terminal spanning-tree vlan vlan-id root primary [diameter net-diameter [hello-time seconds]] Step 3 Step 4 Step 5 end show spanning-tree detail copy running-config startup-config Purpose Enter global configuration mode. Configure a switch to become the root for the specified VLAN. • For vlan-id, you can specify a single VLAN identified by VLAN ID number, a range of VLANs separated by a hyphen, or a series of VLANs separated by a comma. The range is 1 to 1005 when the SI is installed and 1 to 4094 when the EI is installed. • (Optional) For diameter net-diameter, specify the maximum number of switches between any two end stations. The range is 2 to 7. • (Optional) For hello-time seconds, specify the interval in seconds between the generation of configuration messages by the root switch. The range is 1 to 10 seconds; the default is 2 seconds. Note When you enter this command without the optional keywords, the switch recalculates the forward-time, hello-time, max-age, and priority settings. If you had previously configured these parameters, the switch recalculates them. Return to privileged EXEC mode. Verify your entries. (Optional) Save your entries in the configuration file. To return the switch to its default setting, use the no spanning-tree vlan vlan-id root global configuration command. Configuring a Secondary Root Switch When you configure a Catalyst 2950 or Catalyst 2955 switch that supports the extended system ID as the secondary root, the switch priority is modified from the default value (32768) to 28672. The switch is then likely to become the root switch for the specified VLAN if the primary root switch fails. This is assuming that the other network switches use the default switch priority of 32768 and therefore are unlikely to become the root switch. For Catalyst 2950 switches without the extended system ID support (software earlier than Cisco IOS Release 12.1(9)EA1), the switch priority is changed to 16384. You can execute this command on more than one switch to configure multiple backup root switches. Use the same network diameter and hello-time values as you used when you configured the primary root switch with the spanning-tree vlan vlan-id root primary global configuration command. 14-16 Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide 78-11380-10
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