Configuring Spanning Tree Parameters Spanning Tree Operating Modes
OmniSwitch 6800/6850/9000 Network Configuration Guide March 2008 page 7-15
switches and the STP instance for a port's default VLAN on an OmniSwitch will interoperate and success-
fully create a loop-free topology.
802.1q Tagged VLANs
For 802.1q tagged VLANs, Cisco uses a proprietary frame format which differs from the standard IEEE
BPDU format used by Alcatel-Lucent 1X1 mode, thus preventing Spanning Tree topologies for tagged
vlans from interoperating over the 802.1Q trunk.
In order to interoperate with Cisco PVST+ mode, the current Alcatel-Lucent 1x1 mode has an option to
recognize Cisco's proprietary PVST+ BPDUs and allow any user port on an OmniSwitch to send and
receive PVST+ BPDUs, so that loop-free topologies for the tagged VLANs can be created between
OmniSwitch and Cisco switches.
Configuration Overview
You can use the bridge mode 1X1 pvst+ command to globally enable the PVST+ interoperability mode
on an OmniSwitch:
-> bridge mode 1x1 pvst+ enable
To disable the PVST+ mode interoperability mode on an OmniSwitch, use the following command:
-> bridge mode 1x1 pvst+ disable
The bridge port pvst+ command is used to configure how a particular port will handle BPDUs when
connecting to a Cisco switch.
You can use the bridge port pvst+ command with the enable option to configure the port to handle only
the PVST+ BPDUs and IEEE BPDUs for VLAN 1 (Cisco native VLAN for CST). For example:
-> bridge port 1/3 pvst+ enable
The following will cause a port to exit from the enable state:
• When the link status of the port changes.
• When the administrative status of the port changes.
• When the PVST+ status of the port is changed to disable or auto.
You can use the bridge port pvst+ command with the disable option to configure the port to handle only
IEEE BPDUs and to drop all PVST+ BPDUs. For example:
-> bridge port 1/3 pvst+ disable
You can use the bridge port pvst+ command with the auto option to configure the port to handle IEEE
BPDUs initially (i.e., disable state). Once a PVST+ BPDU is received, it will then handle PVST+ BPDUs
and IEEE BPDUs for a Cisco native VLAN. For example:
-> bridge port 1/3 pvst+ auto
Note. By default, a port is configured for PVST+ auto mode on an Omniswitch.
The following show command displays the PVST+ status.
-> show spantree mode
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