Configuring Fault-Tolerant S7 H-Connections Between CP 1623 and S7-400H: IP vs MAC Architecture

In SIMATIC PCS 7 client-server architectures pairing redundant S7-400H controllers (such as CPU 417-5H or CPU 416-5H) with WinCC OS Stations utilizing CP 1623 cards, modern fault-tolerant S7 H-connections are IP-based (ISO-on-TCP RFC 1006) rather than MAC-based (ISO transport). While legacy controllers required external CP 443-1 modules and Layer 2 MAC connections, CPU 417-5H and AS 410-5H controllers feature integrated PROFINET ports supporting native IP-based fault-tolerant S7 connections directly without external CP 443-1 cards. Communication instability (connection dropping upon station restart) occurs when NetPro lacks a properly configured S7 connection (fault-tolerant), switches lack redundant industrial routing, or the PC station lacks the mandatory SIMATIC NET HARDNET-IE S7 REDCONNECT license. Validate hardware configurations and license keys with an authorized Siemens distributor or the Siemens Industry Mall.

Executive Summary

High-availability process facilities running redundant S7-400H controllers (e.g., CPU 417-5H) and WinCC OS Stations equipped with CP 1623 Industrial Ethernet communication processors demand uninterrupted data transmission. Engineers configuring client-server architectures frequently ask whether communication must be MAC-based or IP-based, whether external CP 443-1 processors are mandatory alongside modern CPUs with onboard PROFINET interfaces, and why direct switch connections between CP 1623 and CPU ports exhibit communication instability. This technical article provides the authoritative communication architecture, clarifies the IP vs MAC debate, details REDCONNECT licensing requirements, and provides the step-by-step NetPro configuration workflow.

Architecture and Fundamental Mechanics

The fault-tolerant communication architecture between S7-400H controllers and WinCC PC stations operates on standardized industrial protocols:
1. The Evolution from MAC-Based (ISO) to IP-Based (ISO-on-TCP):
- Legacy S7-400H (V4.x / Early V5.x): CPUs lacked integrated Ethernet ports, requiring external CP 443-1 modules. Fault-tolerant connections were predominantly configured using the ISO Transport Protocol based on Layer 2 MAC addresses.
- Modern S7-400H (CPU 417-5H / CPU 416-5H / AS 410-5H): Integrated PROFINET interfaces support ISO-on-TCP (RFC 1006 / TCP port 102). Modern PCS 7 architectures are completely IP-based. MAC-based addressing is obsolete and unavailable on onboard PROFINET interfaces.
2. Is CP 443-1 Mandatory?
- No. Modern S7-400H CPUs with onboard PROFINET ports do not require external CP 443-1 modules for plant bus communication. Both sub-CPUs connect directly to industrial Ethernet switches (e.g., SCALANCE X-300).
3. The REDCONNECT Driver and Connection Instability:
- Connecting a CP 1623 to an S7-400H pair is not a simple physical link; it requires the SIMATIC NET HARDNET-IE S7 REDCONNECT protocol driver.
- REDCONNECT sets up four cross-coupled logical communication paths between the PC's CP 1623 cards and the two CPUs.
- If the connection in NetPro is configured as a standard S7 connection instead of an 'S7 connection (fault-tolerant)', or if the PC lacks the REDCONNECT license, the connection drops whenever one CPU switches or the PC restarts.
4. Network Redundancy and Switch Topology:
- Redundant plant buses must utilize managed industrial switches configured with Media Redundancy Protocol (MRP) or High-availability Seamless Redundancy (HSR) to prevent broadcast loops.

Step-by-Step Implementation Procedure

Configure AS 410 / S7-400H Onboard PROFINET in HW Config:
a. In SIMATIC Manager, open HW Config for the S7-400H station.
b. Open properties for the onboard PROFINET interface (X1 / PN-IO) on CPU 0: assign IP address (e.g., 192.168.1.10) and subnet Plant_Bus_1.
c. Open properties for the onboard PROFINET interface on CPU 1: assign IP address (e.g., 192.168.1.11) and subnet Plant_Bus_1 (or separate redundant subnet Plant_Bus_2).
d. Save and compile HW Config.
Configure PC Station with CP 1623 in HW Config:
a. Open HW Config for the WinCC OS Station.
b. Place CP 1623 in Slot 1 (and a second CP 1623 in Slot 2 if dual-CP redundancy is used).
c. In CP 1623 properties, assign IP address (e.g., 192.168.1.20) and connect to Plant_Bus_1.
d. Place WinCC Application in Slot 3.
e. Save and compile HW Config.
Configure Fault-Tolerant S7 Connection in NetPro:
a. In SIMATIC Manager, open NetPro.
b. Select WinCC Application under the OS PC Station.
c. In the lower connection table, right-click an empty row and select Insert New Connection.
d. Select the target S7-400H CPU pair.
e. Set 'Type' to S7 connection (fault-tolerant).
f. In the connection properties window, verify that all four communication paths (CP 1623 to CPU 0 and CPU 1) are generated and active.
g. Execute Network -> Save and Compile.
Install SIMATIC NET REDCONNECT License in ALM:
a. On the OS PC station, launch Automation License Manager (ALM).
b. Install the SIMATIC NET HARDNET-IE S7 REDCONNECT license key on drive C:.
Download Configurations and Verify Runtime Communication:
a. Download NetPro connections to both AS sub-CPUs and the PC Station.
b. On the PC station, verify that Station Configuration Editor displays CP 1623 and WinCC Application in 'RUN' mode.
c. Start WinCC Runtime: confirm that process tags update smoothly without communication drops.

Verification

In WinCC Runtime, launch the 'Channel Diagnosis' tool: under SIMATIC S7 Protocol Suite -> Named Connections, verify connection status indicates 'Connected / Redundant'.
Disconnect the network cable from CPU 0: verify that WinCC process data continues updating over CPU 1 without communication alarms or faceplate freezes.
Restart the OS station: verify that upon Windows startup, the fault-tolerant S7 connection establishes automatically within 10 seconds.

Limitations and Operational Precautions

Operating S7 fault-tolerant H-connections over standard commercial office switches without industrial Quality of Service (QoS) and MRP redundancy will cause packet jitter and intermittent connection dropouts. Always deploy certified industrial switches (SCALANCE X).

Engineer FAQ

Are modern S7-400H connections IP-based or MAC-based?

Modern S7-400H connections using onboard PROFINET interfaces (e.g., CPU 417-5H, AS 410-5H) are strictly IP-based (ISO-on-TCP). MAC-based ISO transport is legacy.

Is an external CP 443-1 required for S7-400H WinCC communication?

No. CPUs with integrated PROFINET ports communicate directly over Industrial Ethernet without requiring external CP 443-1 processors.

What causes communication instability between CP 1623 and S7-400H?

Typically caused by configuring a standard S7 connection instead of a fault-tolerant S7 connection in NetPro, or missing the REDCONNECT license.

What license is mandatory for fault-tolerant CP 1623 communication?

SIMATIC NET HARDNET-IE S7 REDCONNECT is mandatory on each PC station communicating with an S7-400H redundant pair.

Can CP 1623 communicate with both CPUs over a single physical cable?

Yes, if both CPUs and the CP 1623 connect to a common industrial Ethernet switch, REDCONNECT establishes logical redundancy over the single physical network, though dual CPs are recommended for complete hardware fault tolerance.