Alcatel-Lucent OmniSwitch 6800 Series - Using 1 X1 Spanning Tree Mode with PVST; Omniswitch PVST+ Interoperability

Spanning Tree Operating Modes Configuring Spanning Tree Parameters
page 7-14 OmniSwitch 6800/6850/9000 Network Configuration Guide March 2008
The following diagram shows a switch running in the 1x1 Spanning Tree mode and shows Spanning Tree
participation for both fixed and tagged ports.
1x1 (single and 802.1Q) Spanning Tree Example
In the above example, STP2 is a single Spanning Tree instance since VLAN 5 contains only fixed ports.
STP 3 and STP 4 are a combination of single and 802.1Q Spanning Tree instances because VLAN 2
contains both fixed and tagged ports. On ports where VLAN 2 is the default VLAN, BPDU are not tagged.
On ports where VLAN 2 is a tagged VLAN, BPDU are also tagged.
Using 1x1 Spanning Tree Mode with PVST+
In order to interoperate with Cisco's proprietary Per Vlan Spanning Tree (PVST+) mode, the current Alca-
tel-Lucent 1x1 Spanning Tree mode has been extended to allow all user ports on an OmniSwitch to trans-
mit and receive either the standard IEEE BPDUs or Cisco's proprietary PVST+ BPDUs. When PVST+
mode is enabled, a user port operates in 1x1 mode initially by default, until it detects a PVST+ BPDU
which will enable that port to operate in the Cisco PVST+ compatible mode automatically. Thus, an
OmniSwitch can have ports running in 1x1 mode when connecting to another OmniSwitch, or ports
running in Cisco PVST+ mode when connecting to a Cisco switch. So both the Alcatel-Lucent 1x1 and
Cisco PVST+ modes can co-exist on the same OmniSwitch and yet interoperate correctly with a Cisco
switch using the standard Spanning Tree protocols (802.1d or 802.1w). Note that in the flat Spanning Tree
mode, both the OmniSwitch and Cisco switches can interoperate seamlessly using the standard MSTP
protocol.
Note. This feature is supported only on OmniSwitch 6850 and 9000.
OmniSwitch PVST+ Interoperability
Native VLAN and OmniSwitch Default VLAN
Cisco uses the standard IEEE BPDU format for the native VLAN (i.e., VLAN 1 by default) over a 802.1Q
trunk. Thus, by default the Common Spanning Tree (CST) instance of the native VLAN 1 for all Cisco
STP 2
STP 3
STP 4
Switch
Port 1/5
Default VLAN 10
VLAN 2 (tagged)
Port 2/5
Default VLAN 2
VLAN 10 (tagged)
Port 2/4
Default VLAN 2
Port 2/3
Default VLAN 5
Port 1/3
Default VLAN 5
Port 1/4
Default VLAN 2