Enabling VBST

Context

The VBST configuration takes effect only when VBST is enabled.

When VBST is enabled on a ring network, VBST immediately starts spanning tree calculation. Parameters such as the switch priority and port priority affect spanning tree calculation, and change of these parameters may cause network flapping. To ensure fast and stable spanning tree calculation, perform basic configurations on the switch and interfaces before enabling VBST.
On a VBST-enabled network, if the link type of the port on the local device is set to access or QinQ, the link type of the port on the remote device must also be the same. If the link types of the ports at both ends are not access or QinQ, the PVIDs of the ports at both ends must be the same. Otherwise, the two devices cannot negotiate the VBST status, and loops cannot be eliminated. For a trunk port, you can run the port trunk pvid vlan command to set the port's PVID.

The PV number is the total number of VLANs into which all VBST-enabled interfaces are added. The VLANs have been established and VBST has been enabled in the VLANs. For example, VBST is enabled on 10 interfaces. Each interface is added into 100 VLANs (all VLANs have been established and VBST is enabled in the VLANs). The number of PVs occupied by all interfaces on the switch is 1000. If the number of occupied PVs exceeds the specifications, the CPU usage may be high. As a result, the switch cannot process tasks in a timely manner, protocol calculation is affected, and the switch cannot be managed by the NMS.

The CPU usage of VBST is in direct proportion to the number of occupied PVs.
You can run the display vbst port-vlan statistics command in any view to check the supported maximum number of PVs of VBST.
The maximum PV number supported in a stack system is the sum of PV quantities supported by member switches. However, a stack system composed of the S5720-EI supports a maximum of 2400 PVs.

Procedure

Run system-view
The system view is displayed.
Run stp mode vbst
The working mode of the switch is set to VBST.

By default, the switch works in MSTP mode.
- The VBST mode cannot be used with the STP/RSTP/MSTP mode.
- If a protected instance in a segment has been configured by the protected-instance (sep segment view) command or a protected instance in an ERPS ring has been configured by the protected-instance (ERPS ring view) command, you must perform the operation of (Optional) Manually Configuring the Mapping between MSTIs and VLANs. Otherwise, the STP working mode cannot be changed to VBST.
- If 1:N (N>1) mapping between MSTIs and VLANs has been configured on the switch, the mapping must be deleted before changing the STP working mode to VBST.
- On the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731S-H, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730S-H, and S6730-H, if stp vpls-subinterface enable has been configured on the switch, the undo stp vpls-subinterface enable command must be run on the interface before changing the STP working mode to VBST.
Run stp enable
Global STP is enabled.

By default, STP is enabled globally.
Run stp vlan { vlan-id1 [ to vlan-id2 ] } &<1-10> enable
VBST is enabled in the specified VLANs.

By default, VBST is enabled in each VLAN.

VBST cannot be enabled in the ignored VLAN or control VLAN used by ERPS, RRPP, SEP, or Smart Link.

If VLAN mapping or VLAN stacking is configured on an interface corresponding to the VLAN, VBST negotiation for this VLAN will fail.
Run interface interface-type interface-number
The interface view is displayed.
Run stp enable
STP is enabled on the interface.

By default, STP is enabled on each switch interface.

STP cannot be used with SEP or Smart Link. An STP-enabled interface cannot join a SEP segment or Smart Link group. Similarly, the interface that has joined the SEP segment or Smart Link group cannot be enabled with STP.