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Configuring Virtualized OS Server Plant Bus Communication: PCIe Passthrough vs VMware VMXNET3

Configuring Virtualized OS Server Plant Bus Communication: PCIe Passthrough vs VMware VMXNET3

In SIMATIC PCS 7 running on VMware ESXi 6.0 and later, direct PCIe hardware passthrough (DirectPath I/O) for legacy communications processors like the CP 1613 or CP 1613 A2 is not supported. For virtualized Operator Stations (OS) and Engineering Stations (ES), Siemens specifies using standard host physical network adapters mapped to virtual switches (vSwitch) with virtual VMXNET3 adapters in the guest OS running the Basic Communication Ethernet (BCE) driver. If ISO transport protocol or Hardnet fault tolerance is mandatory with high-end CP cards, use the PCIe-based CP 1623 with dedicated memory reservation and VT-d passthrough under strict Siemens compatibility guidelines.

Table of Contents

Architecture of Virtualized Plant Bus Interfaces in PCS 7

In SIMATIC PCS 7 virtual environments deployed on VMware vSphere ESXi, establishing high-reliability plant bus communication between virtualized Operator Stations (OS Single Station, OS Server, or Redundant OS Server Pair) and physical SIMATIC S7-400 automation controllers is a core architectural requirement.

The plant bus typically communicates using either the Industrial Ethernet ISO protocol (Layer 2 MAC-based transport) or TCP/IP protocol (Layer 4 transport). In bare-metal installations, dedicated communications processors such as the legacy CP 1613 A2 (6GK1161-3AA01) or the modern CP 1623 (6GK1162-3AA00) provide hardware-assisted communications processing, offloading ISO transport protocol handling from the host CPU.

When transitioning these systems into virtual machines (VMs) running on VMware ESXi 6.0, 6.5, or later hypervisors, virtualization engineers frequently attempt to map physical communications processors directly into the guest OS using VMware DirectPath I/O (PCIe Passthrough). However, hardware passthrough introduces severe hypervisor limitations and hardware incompatibilities that break plant bus communication.

Why Legacy CP 1613 DirectPath I/O Fails on Modern Hypervisors

The CP 1613 and CP 1613 A2 (6GK1161-3AA01) were designed for traditional 32-bit PCI and PCI-X bus standards. On modern server hardware (such as HP ProLiant Gen9 / Gen10 or Dell PowerEdge servers) running VMware ESXi 6.0 or higher:

  1. Lack of PCIe MSI-X Support: Modern hypervisors require Message Signaled Interrupts (MSI-X) and robust Input-Output Memory Management Unit (IOMMU / Intel VT-d) support for DirectPath I/O passthrough. Legacy PCI devices operating through PCI-to-PCIe bridge chips cannot correctly negotiate hypervisor DMA remapping and interrupt virtualization.
  2. End of Hypervisor Certification: Siemens officially ended support for CP 1613 DirectPath I/O passthrough after VMware ESXi 5.1. On ESXi 6.0 and subsequent updates, the hypervisor fails to initialize the card state or drops the virtual PCI bridge connection, resulting in Windows Device Manager reporting error codes (such as Code 10: "This device cannot start") or showing the interface permanently disconnected.
  3. Loss of High Availability Features: DirectPath I/O binds the physical PCI card directly to a single virtual machine. Consequently, crucial virtualization capabilities—such as VMware vSphere vMotion, High Availability (HA), Distributed Resource Scheduler (DRS), and live memory snapshotting—are completely disabled for that VM.

Standard Architecture: Virtual Switch (vSwitch) and VMXNET3 BCE Driver

To eliminate hardware dependencies and unlock full virtualization benefits, Siemens establishes the Basic Communication Ethernet (BCE) architecture as the standard design for virtualized PCS 7 stations:

  • Host Level: The ESXi hypervisor connects to the physical plant bus through dual physical 1 GbE or 10 GbE server network interface cards (NICs) connected to redundant industrial switches (e.g., SCALANCE X-400 or SCALANCE XC-200 series).
  • Hypervisor Level: A dedicated virtual switch (Standard vSwitch or Distributed vSwitch) is configured specifically for the Plant Bus network, binding the physical uplink NICs with active/standby or load-balancing teaming.
  • Guest VM Level: The virtual OS Server is provisioned with a standard VMXNET3 virtual network adapter connected to the Plant Bus vSwitch.
  • Software Layer: Within the guest Windows operating system, the SIMATIC NET PC Software (such as SIMATIC NET V14 or V16) utilizes the BCE driver (Basic Communication Ethernet) with SOFTNET-IE S7 runtime licensing (6GK1704-1CW14-0AA0). Communication between the OS Server and the S7-400 CPU runs via standard TCP/IP protocol or ISO-on-TCP (RFC 1006).

Configuring CP 1623 DirectPath I/O Passthrough When Hardnet Is Required

When plant specifications mandate the ISO Layer 2 transport protocol or when integrating into legacy networks without RFC 1006 support, the PCIe-based CP 1623 (6GK1162-3AA00) can be utilized via VMware DirectPath I/O under strict engineering rules:

  1. BIOS / UEFI Configuration:
    * Enable Intel VT-x (Virtualization Technology) and Intel VT-d (Directed I/O Virtualization) in the server BIOS.
    * Enable 64-bit PCI MMIO allocation above 4 GB.
  2. ESXi Host Configuration:
    * In the vSphere Web Client / ESXi Host Client, navigate to Host > Manage > Hardware > PCI Devices.
    * Locate the Siemens CP 1623 communications processor, toggle DirectPath I/O Passthrough to Active, and reboot the physical ESXi host.
  3. VM Configuration:
    * Power off the target OS Server VM.
    * Edit VM Settings > Add New Device > PCI Device, and select the CP 1623.
    * Mandatory Setting: Expand the Memory section of the VM and select Reserve all guest memory (All locked). DirectPath I/O strictly requires 100% reserved host RAM to guarantee memory pinning for DMA operations.
  4. SIMATIC NET Configuration:
    * Inside Windows, verify that the CP 1623 driver initializes in Device Manager without errors.
    * Open Communication Settings (or Station Configuration Editor) and verify the CP 1623 operates in Configured Mode at Index 3 or 4 matching the PCS 7 Hardware Configuration.

Network Architecture Comparison for Virtualized OS Stations

The following table provides a comprehensive engineering comparison between plant bus interface architectures for virtualized PCS 7 environments:

Feature / CriterionLegacy CP 1613 PassthroughModern CP 1623 DirectPath I/OStandard Virtual Switch (VMXNET3 BCE)Supported HypervisorsESXi 5.0 / 5.1 only (Unsupported on 6.0+)ESXi 6.0, 6.5, 6.7, 7.0 (with restrictions)ESXi 6.0, 6.5, 6.7, 7.0, 8.0, and Hyper-VPhysical Interface32-bit PCI / PCI-XPCIe x1Standard Server NIC (Intel / Broadcom 1/10 GbE)Hardware MLFB6GK1161-3AA016GK1162-3AA00Standard COTS Enterprise Server NICProtocol SupportISO Transport & TCP/IPISO Transport & TCP/IPTCP/IP & ISO-on-TCP (RFC 1006)vSphere vMotion / HANot supportedNot supportedFully supportedMemory ReservationNot applicable100% Locked RAM requiredDynamic or Reserved RAMDriver PackageSIMATIC NET HardnetSIMATIC NET HardnetSIMATIC NET BCE / Softnet-IE S7Recommended DeploymentObsolete; Do Not DeployLegacy ISO networks requiring HardnetStandard Siemens PCS 7 Virtualization Architecture

Step-by-Step Migration from Passthrough to Virtual Switch Architecture

To convert an existing non-functional CP 1613 passthrough configuration to a robust virtual switch architecture:

  1. Remove Passthrough Hardware in VM Settings:
    * Power down the virtual OS Server.
    * In vSphere Client, edit VM settings and delete the PCI Passthrough device entry.
  2. Provision Dedicated Plant Bus Virtual Switch:
    * In ESXi Networking, create a new Standard vSwitch (e.g., vSwitch_PlantBus).
    * Assign two physical server network adapters to this vSwitch for hardware uplink redundancy.
    * Set Promiscuous Mode to Reject, MAC Address Changes to Accept, and Forged Transmits to Accept.
    * Create a Port Group named PG_PlantBus.
  3. Attach VMXNET3 Adapter to VM:
    * In the OS Server VM settings, add a new Network Adapter.
    * Select adapter type VMXNET3 and connect it to PG_PlantBus.
    * Power on the VM and assign the static Industrial Ethernet IP address and subnet mask inside Windows.
  4. Update PCS 7 Hardware Configuration:
    * In SIMATIC Manager, open the SIMATIC PC Station hardware configuration for the OS Server.
    * Replace the CP 1613 or CP 1623 module in the virtual rack (typically Slot 3) with an IE General module (SW V8.2 or matching PCS 7 version).
    * Assign the static IP address and connect the module to the Plant Bus subnet.
  5. Reconfigure Station Configuration Editor:
    * Inside the guest OS, open Station Configuration Editor.
    * Add IE General to the matching slot.
    * In Set PG/PC Interface, set the S7ONLINE access point to PC Internal.local.1 or matching station manager profile.
  6. Compile and Download Network Connections:
    * In SIMATIC Manager, open NetPro, recompile the multi-project connections, and download the updated network routing to the OS Server and S7-400 AS.

Verification

Verify operational readiness of the virtualized plant bus using the following structured checks:
1. Open Windows Device Manager on the virtual machine and ensure the network adapter displays as vmxnet3 Ethernet Adapter (or SIMATIC NET CP 1623 if passthrough is used) without warning icons.
2. In Station Configuration Editor, verify that the station status is "RUNNING" (green icon) and that the IE General or CP 1623 card is in configured mode with identical rack/slot addressing as NetPro.
3. Execute ping -t <AS_IP_Address> from Windows PowerShell to verify sustained Layer 3 reachability without packet drop or excessive jitter (< 2 ms).
4. In WinCC Explorer, activate the OS project and verify in Channel Diagnosis that the Named Connections or Industrial Ethernet channel driver displays a green checkmark with status "Connected" across all configured S7-400 connections.

Limitations and Operational Precautions

  • No Live Migration with Passthrough: If direct PCIe passthrough is deployed with CP 1623, the VM cannot be migrated using VMware vMotion or vSphere Distributed Resource Scheduler (DRS). Any host hardware maintenance requires scheduled VM shutdown.
  • ISO Protocol Routing: Standard layer 3 corporate routers cannot route raw ISO Layer 2 packets. If plant communication spans routed enterprise network segments, configure ISO-on-TCP (RFC 1006) with TCP port 102 open across all intermediate firewalls.
  • Redundant OS Licensing: Ensure redundant virtual OS servers are provisioned with valid WinCC Redundancy licenses (6AV6371-1CF00-0AX0) and independent physical switch uplinks.
  • Commercial Accuracy: All virtualized communication software packages, such as SOFTNET-IE S7 (6GK1704-1CW14-0AA0) or CP 1623 hardware (6GK1162-3AA00), must be validated against Siemens technical sales specifications. Obtain final quotation and licensing verification from an authorized Siemens distributor.

Engineer FAQ

Can I use standard VMware E1000 virtual network adapters instead of VMXNET3 for the plant bus?

No. The legacy Intel E1000 emulation incurs significant CPU overhead, higher packet latency, and has known stability issues with high-volume cyclic industrial communications. Siemens explicitly specifies the paravirtualized VMXNET3 driver for PCS 7 virtual machines to guarantee predictable throughput and minimal jitter.

Does Softnet-IE BCE introduce unacceptable communication latency compared to hardware CP cards?

For typical PCS 7 installations (under 60 AS connections per OS server and cyclic update times of 250 ms to 1 s), the modern VMXNET3 virtual adapter combined with high-performance host CPU cores delivers communication performance virtually indistinguishable from dedicated CP hardware.

Why must VM memory be 100% reserved when using DirectPath I/O passthrough?

PCIe hardware devices perform direct memory access (DMA) using physical host memory addresses. If ESXi were to balloon, compress, or swap the VM's memory pages to disk, incoming network packets from the physical CP card would overwrite unmapped physical memory, triggering a host hypervisor Purple Screen of Death (PSOD) or guest OS crash.

Can two virtual machines on the same ESXi host share a single physical CP 1623 card?

No. DirectPath I/O creates an exclusive, dedicated hardware mapping between the physical PCIe card and a single virtual machine. To share network infrastructure across multiple VMs (e.g., redundant OS servers or OS clients), you must use virtual switches (vSwitch) with standard NIC uplinks.

Technical References

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Related Tags

  • PCS 7 Virtualization
  • VMware ESXi
  • CP 1613
  • CP 1623
  • VMXNET3
  • Plant Bus
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