Alcatel-Lucent 6850-48 网络指南
Spanning Tree Operating Modes
Configuring Spanning Tree Parameters
page 13-14
OmniSwitch AOS Release 6 Network Configuration Guide
September 2009
The following diagram shows a switch running in the 1x1 Spanning Tree mode and shows Spanning Tree
participation for both fixed and tagged ports.
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.
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 allows OmniSwitch ports to transmit 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 proto-
cols (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.
tel-Lucent 1x1 Spanning Tree mode allows OmniSwitch ports to transmit 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 proto-
cols (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.
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 an
802.1Q trunk. Thus, by default the Common Spanning Tree (CST) instance of the native VLAN 1 for all
Cisco switches and the STP instance for a port's default VLAN on an OmniSwitch will interoperate and
successfully create a loop-free topology.
802.1Q trunk. Thus, by default the Common Spanning Tree (CST) instance of the native VLAN 1 for all
Cisco switches and the STP instance for a port's default VLAN on an OmniSwitch will interoperate and
successfully create a loop-free topology.
STP 2
STP 3
STP 4
Switch
Port 1/5
Default VLAN 10
VLAN 2 (tagged)
Default VLAN 10
VLAN 2 (tagged)
Port 2/5
Default VLAN 2
VLAN 10 (tagged)
Default VLAN 2
VLAN 10 (tagged)
Port 2/4
Default VLAN 2
Default VLAN 2
Port 2/3
Default VLAN 5
Default VLAN 5
Port 1/3
Default VLAN 5
Default VLAN 5
Port 1/4
Default VLAN 2
Default VLAN 2