Enabling/Disabling Spanning Tree For A Vlan - Alcatel-Lucent OmniSwitch 6850-48 Network Configuration Manual

Configuring VLANs

Enabling/Disabling Spanning Tree for a VLAN

The spanning tree operating mode set for the switch determines how VLAN ports are evaluated to iden-
tify redundant data paths. If the Spanning Tree switch operating mode is set to flat, then VLAN port
connections are checked against other VLAN port connections for redundant data paths. Note that the
single flat mode STP instance is referred to as instance 1 or the CIST (Common and Internal Spanning
Tree) instance, depending on which STP protocol is active.
In the flat mode, if STP instance 1 or the CIST instance is disabled, then it is disabled for all configured
VLANs. However, disabling STP on an individual VLAN will exclude only that VLAN's ports from the
flat STP algorithm.
If the Spanning Tree operating mode is set to 1x1, there is a single Spanning Tree instance for each VLAN
broadcast domain. Enabling or disabling STP on a VLAN in this mode will include or exclude the VLAN
from the 1x1 STP algorithm.
The vlan stp command is used to enable/disable a Spanning Tree instance for an existing VLAN. In the
following examples, Spanning Tree is disabled on VLAN 255 and enabled on VLAN 755:
-> vlan 255 stp disable
-> vlan 755 stp enable
Note the following when using the vlan stp command. For more information about the vlan stp
command, see the OmniSwitch CLI Reference Guide:
•
If the VLAN ID specified with this command is that of a VLAN that does not exist, the VLAN is auto-
matically created.
•
This command configures the VLAN STP status for both the 1x1 and flat Spanning Tree modes. Using
the 1x1 or flat parameter with this command, configures the STP status only for the mode specified by
the parameter.
•
Up to 253 Spanning Tree instances per switch are supported in the 1x1 Spanning Tree mode. Since
each VLAN with Spanning Tree enabled uses one of these instances, only 253 VLANs can have an
active Spanning Tree instance at any given time.
•
To create more than 253 VLANs on a switch running in the 1x1 Spanning Tree mode, use the vlan stp
disable, vlan 1x1 stp disable, or vlan flat stp disable form of this command to create a VLAN with
Spanning Tree disabled.
STP does not become operationally active on a VLAN unless the VLAN is operationally active, which
occurs when at least one active port is assigned to the VLAN. Also, STP is enabled/disabled on individual
ports. So even if STP is enabled for the VLAN, a port assigned to that VLAN must also have STP
enabled. See Chapter 13, "Configuring Spanning Tree Parameters."
OmniSwitch AOS Release 6 Network Configuration Guide
Enabling/Disabling Spanning Tree for a VLAN
September 2009 page 4-11