Can Two Ethernet Adapters on One Subnet Provide PCS 7 V9.1 OS Client Redundancy?

Two independent Ethernet adapters with addresses on the same subnet do not, by themselves, establish a supported or deterministic failover design for a PCS 7 V9.1 OS client. The forum reply suggests NIC teaming, but the available Siemens reference does not approve an arbitrary adapter team for this configuration. Use the PCS 7 V9.1 network architecture and supported PC/adapter guidance, and confirm the teaming mode and hardware/driver combination with Siemens and the adapter vendor before implementation.

What the proposed design is trying to achieve

The question asks whether two “IE General” interfaces on one OS client, addressed on the same terminal-bus subnet, can provide redundancy if one physical Ethernet port fails. This is a client terminal-bus availability question, not the same as configuring separate terminal, plant/system and redundancy buses on an OS server.

Why two addresses are not a failover mechanism

Two NICs connected to the same subnet may create ambiguous route/interface selection and do not themselves coordinate link failure, address ownership or application reconnection. The fact that Windows shows both interfaces does not mean WinCC/PCS 7 automatically transfers the active communication path. A teaming driver or a separately engineered network failover design would need to be explicitly supported and tested.

Follow the PCS 7 network architecture

Siemens PCS 7 V9.1 configuration guidance treats bus segmentation and station network interfaces as planned architecture. For virtual PCS 7 stations, Siemens' V9.1 virtualization manual calls for the number of adapters appropriate to the station role and places terminal, system and redundancy networks in separate subnets. This supports separating distinct buses; it is not an endorsement of using two same-subnet IE General adapters as an OS-client terminal-bus redundant pair.

Evaluate NIC teaming only as a validated design

Document the OS client role, terminal-bus topology, switch configuration and the exact NIC models/drivers.
Check Siemens' version-specific PC Configuration and network guidance for supported adapter and teaming arrangements.
Check Windows Server/Windows client and NIC vendor support for the proposed team mode, switch configuration and failure behavior.
Obtain confirmation that the selected teaming design is compatible with PCS 7 V9.1 and the deployed WinCC/Simatic Shell configuration.
Test link-loss and recovery behavior on a non-production station, observing WinCC server connection, alarm/message flow, operator control and reconnection—not merely Windows link status.
If no validated team is available, use a supported network architecture or hardware design rather than assigning two same-subnet addresses and expecting automatic failover.

Avoid confusing separate subnets with duplicate interfaces

The separate-subnet guidance for terminal, system and redundancy buses applies to distinct network roles. It does not mean that assigning different IP addresses in one subnet to two adapters automatically creates redundancy. Conversely, do not move a terminal-bus interface into another subnet without updating the complete PCS 7 network configuration.

Verification

In a controlled test, disconnect one physical path and observe whether the client remains connected or recovers within the site's required availability limits. Confirm that connections use the intended route and that server redundancy and OS-client behavior remain correct after failover and restoration. Record results for the exact Windows, NIC driver, teaming mode and PCS 7 release.

Limitations and Operational Precautions

The source provides no NIC make/model, Windows version, switch topology, server architecture or confirmed test result. Its NIC Teaming recommendation is a forum reply, not evidence of Siemens approval for the described same-subnet configuration. Network changes can disrupt OS communication; review with the PCS 7 network owner and test before production deployment.

Engineer FAQ

Will two same-subnet NICs automatically fail over? No such behavior is established by the ticket or the cited PCS 7 guidance.

Is NIC Teaming the confirmed Siemens solution? The forum reply suggests it, but no version-specific approval for this exact setup was established.

Why does PCS 7 use multiple adapters in some architectures? Separate interfaces can serve distinct bus roles; those roles and subnets must follow the applicable PCS 7 architecture.

What must a failover test observe? Actual WinCC/PCS 7 client connectivity, alarm flow, control access and recovery when a link fails and returns.

Can I add another IP on the same terminal bus as a redundancy measure? Do not assume so; verify the complete supported NIC/network design first.

Technical References

Siemens, PCS 7 Compendium Part A – Configuration Guidelines V9.1, network and station configuration: https://support.industry.siemens.com/cs/attachments/109809015/pcs7_compendium_part_a_en-US_en-US.pdf
Siemens, PCS 7 Virtualization V9.1, section 4.2.1 on station network adapters and separate terminal, system and redundancy subnets (applies to virtualized stations): https://support.industry.siemens.com/cs/attachments/109801455/109801455_Manual_PCS7V91_Virtualization_en.pdf
Siemens, PCS 7 PC Configuration manual entry: https://support.industry.siemens.com/cs/ww/en/view/109794377