Enabling/Disabling Spanning Tree For A Vlan - Alcatel OmniSwitch 6800 Series Network Configuration Manual

Enabling/Disabling Spanning Tree for a VLAN

Enabling/Disabling Spanning Tree for a VLAN
When a VLAN is created, an 802.1D standard Spanning Tree Algorithm and Protocol (STP) instance is
enabled for the VLAN by default. The spanning tree operating mode set for the stack determines how
VLAN ports are evaluated to identify 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 0. In this mode, if STP instance 0 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-
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matically created. On all other OmniSwitch platforms, a vid of an existing VLAN is required.
This command configures the VLAN STP status for both the 1x1 and flat Spanning Tree modes. Using
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the 1x1 or flat parameter with this command, configures the STP status only for the mode specified by
the parameter.
Up to 254 Spanning Tree instances per switch are supported in the 1x1 Spanning Tree mode on an
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OmniSwitch 6800. Since each VLAN with Spanning Tree enabled uses one of these instances, only
254 VLANs can have an active Spanning Tree instance at any given time.
To create more than 254 VLANs on an OmniSwitch 6800 running in the 1x1 Spanning Tree mode, use
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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 5, "Configuring Spanning Tree Parameters."
page 4-10 OmniSwitch 6800 Series Network Configuration Guide
Configuring VLANs
November 2004