Spanning Tree Commands 765User GuidelinesDirectLink Rapid Convergence (DRC) can be configured even if the switch isconfigured for MST(RSTP) mode. It only has an effect when the switch isconfigured for STP-PV or RSTP-PV modes. Enabling DRC sets the switchpriority to 49152. Path costs less than 3000 have an additional 3000 addedwhen DRC is enabled. This reduces the probability that the switch willbecome the root switch.DRC immediately changes to an alternate root port on detecting a root portfailure and change the new root port directly to the fowarding state. A TCN issent for this event.After a switchover to an alternate port (new root port), DRC multicasts agratuitous frame on the new root port on behalf of each attached machine sothat the rest of the network knows to use the secondary link to reach thatmachine.RSTP-PV embeds support for IRC and DRC. There is no provision to enableor disable these features in RSTP-PV configured switches.Exampleconsole(config)#spanning-tree uplinkfastspanning-tree vlanUse the spanning-tree vlan command to enable per VLAN spanning tree on aVLAN. Use the no form of the command to remove the VLAN as a separatespanning tree instance.Syntaxspanning-tree vlan {vlan-list}no spanning-tree vlan {vlan-list}•vlan-list–A single VLAN ID or a list of VLAN IDs in comma delineated orrange format with no embedded blanks. Range 1-4094.Default ConfigurationBy default, each configured VLAN is automatically associated with a perVLAN spanning tree instance. If more than eight VLANs are configured, theexcess VLANs do not participate in per VLAN spanning tree.
