How to Provide Redundant PCS 7 V9.1 Terminal-Bus Access for an OS Client

Two Ethernet ports with separate IP addresses on the same subnet are not, by themselves, a documented PCS 7 V9.1 terminal-bus redundancy configuration. Siemens documents a redundant terminal bus based on Parallel Redundancy Protocol (PRP): each participating PC station uses two separate network adapters connected to two separate redundant networks, with SIMATIC NET SOFTNET-IE RNA organizing the duplicated communications. Select released, suitable adapters and follow the V9.1 configuration manual for the client and network design.

Why two IP addresses are not enough

The question concerns failure of one Ethernet port on a single PCS 7 V9.1 OS client. A second interface address alone does not show that PCS 7 and its communication software will detect failure and move the client's traffic to another path. Siemens' V9.1 High Availability manual identifies PRP as its redundant, high-availability terminal-bus approach and explains that SOFTNET-IE RNA duplicates protocols over two separate networks. It does not identify ordinary Windows NIC teaming or two independent same-subnet addresses as an equivalent configuration.

Prerequisites

Before designing the change, confirm the installed PCS 7 release and its Readme, supported PC/network adapters, and the terminal-bus topology. Siemens' V9.1 High Availability manual requires two free, separate Ethernet adapters and exactly one SOFTNET-IE RNA software license per PC for the PRP PC connection. It states that SOFTNET-IE RNA can be installed through PCS 7 system setup. The PCS 7 V9.1 PC Configuration manual directs engineers to verify that each selected communication module is suitable for the chosen terminal-bus concept.

Configure the PRP terminal bus

Design two separate terminal-bus networks, LAN A and LAN B, so the two adapter paths do not depend on the same failed link or component.
On each PC station participating in the redundant terminal-bus design, provide two separate supported Ethernet adapters. The V9.1 High Availability manual requires two adapters and SOFTNET-IE RNA on each redundantly connected PC station.
Install and configure SIMATIC NET SOFTNET-IE RNA according to the applicable V9.1 and SIMATIC NET operating instructions. The High Availability manual states that NetPro and HW Config do not configure the terminal bus; SOFTNET-IE RNA is used to connect PC stations to the separate redundant networks.
Connect the PC station's first adapter to LAN A and its second adapter to LAN B, then configure the software and partner stations as documented for the installed SOFTNET-IE RNA version.
Confirm that the selected network adapters and switches are released for the target PCS 7 configuration. Siemens' PC Configuration V9.1 manual lists Parallel Redundancy Protocol as the terminal-bus redundancy option and directs users to verify component suitability.

The exact adapter, switch, software version, and address design must come from the applicable released-module list and SIMATIC NET instructions; the ticket does not supply the PC model or network components.

What redundancy this provides

With PRP configured across the two separate networks, the V9.1 High Availability manual says communications are duplicated and the receiver uses the first incoming copy. It states that a fault on one bus has no effect on the redundant bus and that the transmission route can remain operational when a network component fails. This protects only the failures covered by the configured independent paths; a shared power source, switch, cable route, or other common component can still defeat redundancy.

Verification

In a maintenance or commissioning window, verify that the OS client communicates normally over the configured PRP terminal bus. Use the site-approved test procedure to disconnect one adapter path or otherwise simulate its failure, then confirm that communication continues over the remaining network and returns to the intended redundant state after restoration. Check communication and alarms at both ends. Do not infer successful failover from Windows reporting both adapters as connected.

Limitations and Operational Precautions

The documented PCS 7 V9.1 approach is PRP using SOFTNET-IE RNA, separate adapters, and separate networks. It requires suitable released hardware and licensing. The cited manuals do not provide enough information to prescribe addresses for the example subnet 192.168.1.0, the precise NIC models, or a Windows teaming setup. Do not place both paths on a shared switch, cable route, or power source if the design is meant to tolerate those component failures. Validate software compatibility and follow site change control before changing a running OS client.

Engineer FAQ

For one OS client with a failed adapter as the target fault, the relevant design is redundant terminal-bus communication at the PC/network level. Siemens' V9.1 manuals describe PRP through SOFTNET-IE RNA across two separate networks. This differs from configuring two independent IP interfaces and expecting PCS 7 to switch between them.

Technical References

Siemens, High Availability Process Control Systems (V9.1), Function Manual, section 4.3.3.4, “Redundant, high availability terminal bus based on the Parallel Redundancy Protocol (PRP),” and section 5.3.2.1, “How to configure the redundant terminal bus on the basis of the Parallel Redundancy Protocol,” A5E50318344-AA: https://cache.industry.siemens.com/dl/files/373/109794373/att_1057410/v1/ps7red_b_en-US.pdf
Siemens, PCS 7 - PC Configuration (V9.1), Installation Manual, section 4.3, “Components for connection to the terminal bus/plant bus,” A5E50303177-AA: https://cache.industry.siemens.com/dl/files/377/109794377/att_1057431/v1/ps7pck_b_en-US.pdf

How to Provide Redundant PCS 7 V9.1 Terminal-Bus Access for an OS Client