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.

Feature Support in V200R019C10

All models of S2720, S5700, and S6700 series switches support VBST.

For details about software mappings, visit Hardware Query Tool and search for the desired product model.

Feature Limitations

• Table 1 lists the specifications of VBST.

  Table 1 Specifications of VBST

  Item	Specification
  Number of protected VLANs	S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-HI, S6730-H, S6730S-H, S6730-S, and S6730S-S: 128 in earlier versions of V200R019C10. 300 in V200R019C10 and later versions. S5735-L, S5735S-L, S5735S-L-M, S5735-S, S5735-S-I, and S5735S-S: 126 Other models: 128
  PV quantity (The PV quantity 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.)	In V200R009 and earlier versions, the S5720-HI, S6720-EI, and S6720S-EI support a maximum of 1200 PVs, the S5720-EI supports a maximum of 600 PVs, and other switches support a maximum of 300 PVs. In V200R010 and V200R011, the S5720-HI, S6720-EI, and S6720S-EI support a maximum of 1200 PVs, the S5730-SI, S5730S-EI, S6720-LI, S6720S-LI, S6720-SI, S6720S-SI, and S5720-EI support a maximum of 1000 PVs, the S2750-EI and S5700-LI support a maximum of 300 PVs, and other switches support a maximum of 600 PVs. In V200R012 and later versions, you can run the display vbst port-vlan statistics command to check the supported PV quantity. The maximum PV quantity 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. For an Eth-Trunk, the PV quantity supported by the system is that supported by the master switch. NOTICE: The CPU usage of VBST is in direct proportion to the PV quantity. 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 even the switch cannot be managed by the NMS.

• In versions earlier than V200R019C00, the switch does not support association between VBST and VPLS. In V200R019C00 and later versions, when a VLANIF interface is connected to a VPLS network, the switch supports association between VBST and VPLS.

• 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 ports 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 VLAN mapping or VLAN stacking is configured on an interface corresponding to the VLAN, VBST negotiation for this VLAN will fail.

• 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 the number of MSTIs that are dynamically specified exceeds the number of protected VLANs, STP is displayed as 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 × (Hello Time + 1.0 second)

• After all ports are configured as edge ports and BPDU filter ports in the system view, no 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 remote 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/QinQ, 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/QinQ, 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 VLAN that a hybrid port joins in untagged mode is not a VLAN specified by the port's PVID, the port cannot forward VBST BPDUs normally. As a result, VBST cannot eliminate network loops. Therefore, hybrid ports are not recommended in VBST.

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