(Optional) Manually Configuring the Mapping Between MSTIs and VLANs
Context
Based on the mappings between MSTIs and VLANs of MSTP, VBST maps each MSTI to a VLAN to establish 1:1 mapping. The 1:1 mapping between MSTIs and VLANs is used only by the switch to determine the VBST forwarding status. This does not mean that VBST supports multi-instance.
You can manually configure the mapping between MSTIs and VLANs on the switch. If a static mapping is also configured for a VLAN, the static mapping takes effect.
After VBST is enabled, the system dynamically allocates instance IDs to existing or new VLANs in ascending order. The dynamically specified mapping cannot be changed manually. After a VLAN is deleted or STP is disabled globally, its mapping is automatically deleted.
When the number of VBST instances exceeds the capability supported by the device, the VBST function does not take effect in a new VLAN by default, and an alarm is generated. To enable VBST for the VLAN, run the undo vlan command to release resources used by other VLANs. When the number of VLANs that support VBST decreases to less than 95% of the upper limit, the alarm is cleared and the system automatically reallocates resources.
The number of VBST instances supported by a device is calculated according to the following formula: Number of VBST instances supported by a device = Number of static instances + Number of dynamic instances
For CE12800 series switches:
When the card interoperability mode is enhanced, the device supports a maximum of 240 VBST instances, among which a maximum of 63 static instances can be configured.
If the undo set forward capability enhanced command is used to switch the card interoperability mode to non-enhanced, it is recommended that a maximum of 60 instances be configured.
When the card interoperability mode is non-enhanced, the device supports a maximum of 60 VBST instances.
The CE12800E equipped with FD-X series cards supports a maximum of 500 VBST instances, among which a maximum of 63 static instances can be configured.
The following steps are performed to manually configure the mapping between MSTIs and VLANs.
Procedure
- Run system-view
The system view is displayed.
- Run stp region-configuration
The MST region view is displayed.
- Run instance instance-id vlan vlan-id
1:1 mapping between MSTIs and VLANs is configured.
By default, all VLANs in an MST region are mapped to MSTI 0.
- After this step is performed, the dynamic mapping between MSTIs and VLANs cannot be canceled even if VLANs are deleted or STP is disabled globally.
- The 1:1 mapping between instances and VLANs is configured in the system. When the mapping between multiple VLANs and static instances is configured at one time, the system may display the message "Error: Can not map more than one VLAN to an instance." This is because the mapping between multiple VLANs and instances is submitted at one time. Actually, the mapping between multiple VLANs and instances should be submitted one by one. In this case, resource allocation remains unchanged, and multiple VLANs are mapped to one instance. You are advised to run the display stp vlan instance command to check the mapping between VLANs and instances first.
- Instance 4094 are reserved in VBST mode to prevent temporary loops. You cannot use the instance instance-id vlan vlan-id command to configure the mapping between instance 4094 and a VLAN. Before switching the VBST mode, delete the configuration of instance 4094 or use an available instance to replace instance 4094.
- When excess VLANs are configured and static instances are deleted, the system may automatically allocate resources. In this case, the VLANs to which dynamic instances are not allocated preferentially occupy idle instances. If the rollback configuration { to { commit-id commit-id | label label | file file-name } | last number-of-commits } command is executed to perform rollback to reallocate resources. The configuration rollback may fail because resource allocation has been complete. Before configuration rollback, run the display configuration commit changes command to check the configuration change in the configuration rollback point to determine whether the configuration can be rolled back to the expected historical state. If some configurations fail to be rolled back, run the display configuration rollback result command to check these configurations and the messages generated during configuration execution. Then manually restore the configuration.
- Run commit
The configuration is committed.