Licensing Requirements and Limitations for VBST

Involved Network Elements

Other network elements also need to support VBST.

Licensing Requirements

VBST is a basic feature of a switch and is not under license control.

Version Requirements

To know details about software mappings, see Hardware Query Tool.

Feature Limitations

• Table 16-4 describes the specifications of VBST.

  Table 16-4  Specifications of VBST

  Item	Specification
  Number of protected VLANs	128
  PV quantity (production of number of VBST-enabled ports and number of VLANs)	The CPU usage of VBST is in direct proportion to the PV quantity. EE series, and X series cards, ET1D2L02QSC0, ET1D2L08QSC0, and ET1D2X48SEC0 cards support up to 1200 PVs, and other cards support up to 300 PVs. The number of PVs supported by the switch is the total number of PVs supported by running cards of the switch. For an Eth-Trunk, in V200R009 and earlier versions, the device supports up to 300 PVs. In later versions of V200R009, the device supports up to 1000 PVs. NOTICE: If the PV quantity exceeds the specifications, the CPU usage may exceed the threshold. As a result, the switch cannot process tasks in a timely manner, protocol calculation is affected, and even the device cannot be managed by the NMS.

• The switch does not support association between VBST and VPLS.

• When VBST is enabled on a ring network, VBST immediately starts spanning tree calculation. Parameters such as the device priority and port priority affect spanning tree calculation, and the 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.

• If the protected instance has been configured in a SEP segment or ERPS ring but the mapping between protected instances and VLANs is not configured, VBST cannot be enabled.

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

• If 1:N (N>1) mapping between MSTIs and VLANs has been configured on the switch, delete the mapping before changing the STP working mode to VBST.
• If the stp vpls-subinterface enable command has been configured on a switch, run the undo stp vpls-subinterface enable command on an interface before changing the STP working mode to VBST.

• If the device has been configured as the root bridge or secondary root bridge, run the undo stp vlan { vlan-id1 [ to vlan-id2 ] } &<1-10> root command to disable the root bridge or secondary root bridge function and run the stp vlan { vlan-id1 [ to vlan-id2 ] } &<1-10> priority priority command to change the device priority.

• When more than 128 MSTIs are dynamically specified, STP is disabled in a created VLAN in the configuration file, for example, stp vlan 100 disable.

• To prevent frequent network flapping, ensure that the values of Hello time, Forward Delay, and Max Age conform to the following formulas:

  • 2 x (Forward Delay - 1.0 second) ≥ Max Age

  • Max Age ≥ 2 x (Hello Time + 1.0 second)

• It is recommended that fast convergence in normal mode be used. If fast is used, frequently deleting ARP entries may result in 100% CPU usage of the MPU and LPU. As a result, packet processing expires and network flapping occurs.

• After all ports are configured as edge ports and BPDU filter ports in the system view, none of ports on the switch send BPDUs or negotiate the VBST status with directly connected ports on the remote device. All ports are in forwarding state. This may cause loops on the network, leading to broadcast storms. Exercise caution when you configure a port as an edge port and BPDU filter port.

• After a port is configured as an edge port and BPDU filter port in the interface view, the port does not process or send BPDUs. The port cannot negotiate the VBST status with the directly connected port on the peer device. Exercise caution when you configure a port as an edge port and BPDU filter port.

• Root protection takes effect only on designated ports.

• In VBST networking, if the link type of the local interface is set to access, the link type of the remote interface must also be set to access; if the link types of the local and remote interfaces are both not access, the PVIDs of the two interfaces must be the same. Otherwise, the two devices cannot negotiate the VBST status, failing to achieve loop prevention.

• If a switch has an alternate port (backup of the root port), configure loop protection on both the root port and alternate port.