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Frank Zhang
Frank Zhang

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Cisco and Huawei STP Interoperability in Industrial Networks: A Practical VBST Approach

#cisco #community #network

In industrial network upgrades, a very common situation is that the existing core network has been running on Cisco switches for years, while newly added production lines, PLC cabinets, industrial PCs, or monitoring devices may use Huawei switches due to procurement cycles, cost considerations, or supply-chain constraints.

In this kind of environment, the real challenge is often not VLAN configuration, but Spanning Tree Protocol interoperability.

A Typical Industrial Network Scenario

Consider a manufacturing workshop where the existing network is based on Cisco switches:

                Cisco Core-1
                      │
              ┌───────┴───────┐
              │               │
          Cisco SW         Cisco SW
                              │
                        ┌─────┴─────┐
                        │           │
                    Huawei SW ===== Huawei SW
                        │           │
                    PLC / HMI   Industrial PCs / Cameras
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To improve production network availability, redundant links may exist between the two workshop switches and between the access layer and the core network.

The workshop may also use multiple VLANs:

VLAN 10   PLC Control Network
VLAN 20   HMI / SCADA Network
VLAN 30   Industrial Computers
VLAN 40   Video Surveillance
VLAN 99   Network Management
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If the existing Cisco core is running PVST+ or Rapid PVST+, simply configuring standard MSTP on the newly added Huawei switches requires careful consideration of how the two spanning-tree mechanisms interact.

Why VBST Can Be a Better Fit

One of the defining characteristics of Cisco PVST/PVST+ is:

Each VLAN can have its own independent spanning-tree instance.

For example:

VLAN 10 → STP Instance 10
VLAN 20 → STP Instance 20
VLAN 30 → STP Instance 30
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This means that different VLANs can even use different forwarding paths.

Huawei switches that support VBST (VLAN-Based Spanning Tree) can follow a similar model by creating independent spanning-tree instances for individual VLANs.

On switch models and software versions that support the required functionality, VBST can be used to interoperate with Cisco PVST+/Rapid PVST+ networks.

This allows newly introduced Huawei switches to preserve the spanning-tree design logic of the existing Cisco network as much as possible, without forcing a redesign of the entire core STP architecture just to accommodate a few new access switches.

Conceptually, the relationship can be viewed like this:

Cisco                           Huawei
PVST+/Rapid PVST+               VBST
        │                         │
        ├── VLAN 10 STP ──────────┤
        ├── VLAN 20 STP ──────────┤
        └── VLAN 30 STP ──────────┤
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For industrial networks that have been operating reliably for many years, this is important.

The first principle of expansion is usually not to adopt the newest architecture, but to minimize the impact on the existing production network.

Why You Should Not Automatically Choose MSTP

MSTP is, of course, a mature and standardized protocol, and it is well suited to large-scale networks.

Its design philosophy, however, is different:

Multiple VLANs
      ↓
Mapped to a smaller number of MST Instances
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For example:

VLAN 10, 20 → MSTI 1
VLAN 30, 40 → MSTI 2
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Cisco PVST+, on the other hand, is closer to:

One VLAN
    ↓
One STP Instance
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Therefore, when adding new switches to an existing Cisco PVST+/Rapid PVST+ network, configuring the new devices directly with MSTP does not necessarily mean the network will fail.

However, the spanning-tree behavior at the boundary, root bridge election, and blocked forwarding paths for different VLANs all require additional validation.

In a production environment where PLCs, robots, MES terminals, and other industrial systems are already online, changes like this should be handled very carefully.

What Matters Most During Industrial Network Deployment

Protocol compatibility is only the first step.

For example, suppose the original network design specifies:

Cisco Core-1
     ↓
VLAN 10 Root Primary
VLAN 20 Root Primary
VLAN 30 Root Primary
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After introducing Huawei switches, you must make sure that an inappropriate default STP priority does not cause an access-layer switch in the workshop to unexpectedly become the Root Bridge.

At minimum, the following should be verified:

Is the Root Bridge still located at the core layer?
        ↓
Does the STP topology for each VLAN match the design?
        ↓
Are redundant links correctly placed into Blocking/Discarding state?
        ↓
Can the network converge quickly after the primary link fails?
        ↓
After the link is restored, are there any loops or excessive MAC flapping events?
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In an industrial environment, I strongly recommend performing an actual link-failure test:

Normal Operation
      ↓
Disconnect the Primary Uplink
      ↓
Observe the Backup Link Take Over
      ↓
Check PLC / HMI Communication
      ↓
Restore the Primary Link
      ↓
Check STP, MAC Address Tables, and Application Status Again
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In an office network, a network interruption lasting several seconds may simply feel like a slow-loading webpage.

In a production network, however, it may result in HMI disconnections, PLC communication alarms, or even production interruptions.

A More Practical Design Principle

For a mixed Cisco and Huawei industrial network, the design principle can be summarized in one sentence:

Keep the core unchanged and make the edge compatible. First ensure consistent spanning-tree behavior, then consider architecture standardization later.

If an existing Cisco PVST+/Rapid PVST+ network has already been running reliably, and the requirement is simply to add several Huawei switches that support VBST, using VBST to continue the existing Per-VLAN STP design can often introduce less risk than immediately migrating the entire production network to a different spanning-tree architecture.

When the core switching infrastructure is eventually replaced, the network can then be redesigned in a more systematic way using technologies such as MSTP, stacking, MLAG, or other redundancy architectures.

The most important principle in industrial network upgrades is not that newer protocols are always better.

It is to:

maintain compatibility with the existing network, control the scope of change, and ensure that the failure of any single link does not disrupt production.

Note: VBST support and interoperability with Cisco PVST+/Rapid PVST+ depend on the specific Huawei switch model, VRP software version, and interface configuration. Before deploying this design in a production environment, verify support for the actual hardware and software versions being used, and validate the STP root bridge, trunk VLANs, and link-failover behavior in a test environment.

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