Users Guide

Layer 2 Switching Commands 783
that the rest of the network knows to use the secondary link to reach that
machine.
DRC is disabled when the administrator modifies the spanning-tree priority
of a VLAN and is re-enabled only when the default priority is restored.
Configuration of the bridge priority is given preference over configuration of
the root primary or root secondary configuration, which is given preference
over the configuration of DirectLink Rapid Convergence.
RSTP-PV embeds support for IRC and DRC. There is no provision to enable
or disable these features in RSTP-PV configured switches.
DRC is most useful for enterprise wiring-closet topologies with a limited
number of VLANs. Do not enable DRC on backbone or distribution layer
switches as DRC is not capable of completing the reconfiguration of large
networks within the max age time.
Example
console(config)#spanning-tree uplinkfast
spanning-tree vlan
Use the spanning-tree vlan command to enable per VLAN spanning tree on a
VLAN. Use the no form of the command to remove the VLAN as a separate
spanning tree instance.
Syntax
spanning-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 or
range format with no embedded blanks. Range 1-4093.
Default Configuration
By default, each configured VLAN is automatically associated with a per
VLAN spanning tree instance. If more than eight VLANs are configured, the
excess VLANs do not participate in per VLAN spanning tree.