Enabling/Disabling The Vlan Bpdu Switching Status; Configuring Vlan Bridge Priority; Configuring Vlan Bridge Hello Time - Alcatel OmniSwitch 6800 Series Network Configuration Manual

Configuring STP VLAN Parameters

Enabling/Disabling the VLAN BPDU Switching Status

By default, BPDU are not switched on ports associated with Spanning Tree disabled VLANs. This may
result in a network loop if the VLAN has redundant paths to one or more other switches. Allowing Span-
ning Tree disabled VLANs to forward BPDU to all ports in the VLAN, can help to avoid this problem.
To enable or disable BPDU switching on a VLAN, enter bridge followed by an existing VLAN ID (or 0 if
using the flat STP instance) then bpdu-switching followed by enable or disable. For example, the follow-
ing commands enable BPDU switching on VLAN 10, disable it on VLAN 20, and enable it on the flat STP
instance:
-> bridge 10 bpdu-switching enable
-> bridge 20 bpdu-switching disable
-> bridge 0 bpdu-switching enable
Note. Make sure that disabling BPDU switching on a Spanning Tree disabled VLAN will not cause
network loops to go undetected.

Configuring VLAN Bridge Priority

A bridge is identified within the Spanning Tree by its bridge ID (an eight byte hex number). The first two
bytes of the bridge ID contain a priority value and the remaining six bytes contain a bridge MAC address.
The bridge priority is used to determine which bridge will serve as the root of the Spanning Tree. The
lower the priority value, the higher the priority. If more than one bridge have the same priority, then the
bridge with the lowest MAC address becomes the root.
Note. Configuring a VLAN with a priority value that will cause the VLAN to become the root is recom-
mended, instead of relying on the STP comparison of switch base MAC addresses to determine the root.
If the switch is running in the 1x1 Spanning Tree mode, then a priority value is assigned to each VLAN.
When a VLAN is created, STP is enabled and the VLAN bridge priority defaults to 32768. If the switch is
running in the flat Spanning Tree mode, the priority is assigned to instance 0.
To change the VLAN bridge priority, enter bridge followed by an existing VLAN ID (or 0 if using the flat
STP instance) then priority followed by a numerical value between 0 and 65535 that is a multipe of 4096.
For example, the following commands change the priority for VLAN 455 to 16384 and priority for the flat
STP instance to 12288:
-> bridge 455 priority 16384
-> bridge 0 priority 12288
To view the VLAN bridge priority value, use the
this command, see the OmniSwitch CLI Reference Guide.

Configuring VLAN Bridge Hello Time

The VLAN bridge hello time interval is the number of seconds a bridge will wait between transmissions of
Configuration BPDU. When a bridge is attempting to become the root or if it has become the root or a
designated bridge, it sends Configuration BPDU out all forwarding ports once every hello time value.
page 5-12
show spantree
OmniSwitch 6800 Series Network Configuration Guide
Configuring Spanning Tree Parameters
command. For more information about
November 2004