Configuring Redundant Terminal Bus in PCS 7 V9.0 with SOFTNET-IE RNA and PRP

In SIMATIC PCS 7 V9.0, establishing a redundant Terminal Bus is officially implemented using Parallel Redundancy Protocol (PRP according to IEC 62439-3) via SIMATIC NET SOFTNET-IE RNA software (6GK1711-1EW14-0AA0) or dedicated hardware redundancy packages (6ES7652-0XX01-1XF1). When SOFTNET-IE RNA is installed on an Industrial PC (IPC) utilizing two onboard commercial network interface cards, the PC functions as a Doubly Attached Node executing PRP (DANP) and connects directly to two completely independent, physically separated local area networks (LAN A and LAN B) built with standard SCALANCE switches. SCALANCE X-204RNA redundancy boxes (6GK5204-0BA00-2KB2) are only required for Singly Attached Nodes (SANs) lacking RNA software, such as network printers or third-party devices.

PRP Redundancy Fundamentals (IEC 62439-3)

In SIMATIC PCS 7, the Terminal Bus interconnects Engineering Stations, OS Servers, OS Clients, and Process Historians. To ensure that client-server visualization survives physical cable cuts, switch power losses, or adapter failures, plant architectures mandate a redundant terminal bus.

Beginning with PCS 7 V9.0 and Windows 10 Enterprise / Windows Server 2016, Siemens standardized on the Parallel Redundancy Protocol (PRP) defined in international standard IEC 62439-3. Unlike legacy spanning-tree or teaming protocols that require a reconfiguration timeout when a fault occurs, PRP provides zero-millisecond seamless redundancy (bumpless switchover).

Under PRP, every transmitted Ethernet frame is duplicated at the protocol layer. One frame is transmitted over local area network A (LAN A), and an identical copy is transmitted simultaneously over local area network B (LAN B). The receiving station accepts whichever packet arrives first and discards the duplicate, ensuring zero packet loss even if one entire network tier fails.

SOFTNET-IE RNA vs Hardware Adapter Teaming

Historically, PCS 7 terminal bus redundancy relied on Intel network adapter teaming (Intel PROSet Advanced Network Services) using dedicated hardware packages. In modern PCS 7 releases, software-based PRP via SIMATIC NET SOFTNET-IE RNA is the primary standard:

Redundancy ArchitectureOrder Number (MLFB)Required HardwareSwitch RequirementsFailover TimeSIMATIC NET SOFTNET-IE RNA V14 / V156GK1711-1EW14-0AA0Standard IPC with 2 standard commercial NICsStandard SCALANCE X switches (LAN A & LAN B)0 ms (Seamless, bumpless IEC 62439-3 PRP)SIMATIC PCS 7 Redundant Terminal Bus Package6ES7652-0XX01-1XF12x Intel PCIe Gigabit desktop/server NICsStandard switches supporting Intel ANS TeamingDependent on driver teaming failover (1-3 sec)SCALANCE X-204RNA Redundancy Box6GK5204-0BA00-2KB2Hardware appliance for Singly Attached Nodes (SAN)Bridges single-NIC devices into redundant PRP LANs0 ms PRP conversion for legacy devices

[!IMPORTANT]
Commercial Accuracy Guardrail: Software licensing rules, package contents, and pricing vary by region and contract status. Software packages, order numbers, and capacity limits must be verified against current Siemens Industry Mall catalogs and validated through an authorized Siemens distributor quotation prior to procurement.

When using an IPC equipped with two standard onboard Gigabit LAN interfaces, installing SOFTNET-IE RNA (6GK1711-1EW14-0AA0) enables PRP redundancy without requiring proprietary PCIe network cards.

Switch Architecture: Standard SCALANCE vs SCALANCE X-204RNA

A frequent question among plant engineers is whether dedicated SCALANCE X-204RNA switches are mandatory when using SOFTNET-IE RNA.

The answer depends on whether the connected nodes are DANP or SAN:

Doubly Attached Nodes executing PRP (DANP): Any PC (OS Server, OS Client, ES) running SOFTNET-IE RNA with two network adapters acts as a native DANP. It duplicates frames internally and connects one cable to LAN A and one cable to LAN B. These PCs connect directly to standard industrial switches (such as SCALANCE XC208 6GK5208-0BA00-2AC2 or SCALANCE XB208 6GK5208-0BA00-2AB2). Dedicated RNA switches are not required for these stations.
Singly Attached Nodes (SAN): Devices with only a single network adapter—such as network printers, third-party modems, or legacy OS clients without RNA software—cannot duplicate packets. To connect a SAN to a redundant PRP network without losing redundancy, a SCALANCE X-204RNA (6GK5204-0BA00-2KB2) redundancy box is required. The X-204RNA accepts frames from the single device and duplicates them across LAN A and LAN B.

Step-by-Step Configuration of LAN A and LAN B

To commission a redundant Terminal Bus using SOFTNET-IE RNA in PCS 7 V9.0:

Physical Network Isolation: Build two physically separate Ethernet networks. Install Switch Pair A for LAN A and Switch Pair B for LAN B. Crucial rule: Never connect an Ethernet cable between LAN A switches and LAN B switches. PRP requires completely isolated broadcast domains.
Install SOFTNET-IE RNA:
- Install SIMATIC NET SOFTNET-IE RNA on the IPC.
- Transfer the license key (6GK1711-1EW14-0AA0) to local drive C: via Automation License Manager.
Configure the Virtual RNA Adapter:
- Open Communication Settings (or SOFTNET-IE RNA Configuration Console).
- Create a virtual RNA adapter.
- Assign physical Network Adapter 1 to LAN A, and Network Adapter 2 to LAN B.
- Assign the static Terminal Bus IP address, subnet mask, and DNS settings exclusively to the virtual RNA adapter in Windows Network Connections (ncpa.cpl).
Bind Simatic Shell:
- Open Windows Explorer -> Simatic Shell -> Settings.
- Select the newly created virtual RNA adapter as the active communication interface for WinCC.

Verification

To verify redundant terminal bus operation:
1. In the SOFTNET-IE RNA diagnostic console, verify that both LAN A and LAN B show 'Link Up' and are actively transmitting and receiving duplicated frames.
2. Open Command Prompt and initiate a continuous ping to an OS Server: ping -t <Server_IP>.
3. Physically disconnect the network cable from LAN A on the Engineering Station; confirm that the ping stream does not drop a single packet (0 ms failover).
4. Reconnect LAN A and disconnect LAN B; confirm continuous communication without interruption or WinCC reconnection events.

Limitations and Operational Precautions

Never create a physical or logical cross-connection between LAN A and LAN B switches (such as bridging switches or trunking them together). Connecting LAN A to LAN B creates broadcast loops and packet duplicate reflection that will overwhelm the network and crash communication processors. Ensure both LAN adapters on each IPC operate at identical speeds (1 Gbps full-duplex) to prevent frame timing skew.

Engineer FAQ

Do I need SCALANCE X-204RNA switches if all my PCs run SOFTNET-IE RNA?

No. If all PCs run SOFTNET-IE RNA, they duplicate frames internally. You only need standard industrial switches (such as SCALANCE XC-200 or X-300) for LAN A and LAN B.

When is SCALANCE X-204RNA required?

SCALANCE X-204RNA is only required for Singly Attached Nodes (SAN)—devices with a single network card (such as office PCs, printers, or legacy PLCs) that must connect to the PRP redundant terminal bus.

Can LAN A and LAN B use different IP subnets?

No. In PRP (IEC 62439-3), both LAN A and LAN B share the identical IP subnet and MAC addresses. The separation is purely physical (two isolated sets of switches).