Resolving WinCC 0xFFDF 410E on SIMATIC TDC CPU 551 via Broadcom

1. Problem Statement

A WinCC V7.x DataManager Runtime running on an HP ProLiant DL380p Gen8 with a Broadcom NetXtreme Ethernet controller repeatedly drops and re-establishes the S7 connection to a SIMATIC TDC CPU 551 rack. The fault is reproducible on two identical DL380p Gen8 servers. The same WinCC project, on the same hardware but with an Intel Ethernet controller, runs without the fault. The same Broadcom adapters on the same servers talking to S7-300/400 controllers also run without the fault. The interaction is therefore specific to the WinCC ↔ SIMATIC TDC path over that NIC and is not a generic WinCC or Broadcom defect.

The fault is reported in PCS 7 V8.0 SP2 diagnostics with the 32-bit status word 0xFFDF 410E. Sample log entries from the failing system:

SIMATIC_S7_Protocol_Suite_01.LOG:
2016-05-04 09:46:05,613 ERROR    Connectionerror 1 "F1":       Errorcode 0xFFDF 410E!
2016-05-04 09:58:01,697 ERROR    Connectionerror 1 "TCP_TDC":  Errorcode 0xFFDF 410E!
2016-05-04 10:09:29,384 ERROR    Connectionerror 1 "R1":       Errorcode 0xFFDF 410E!

WinCC_Sys_02.LOG:
255,04.05.2016,09:46:05:666,1000204,4,,RG-OS-RED1,DataManager Runtime,F1       Connection 'F1'       disconnected
255,04.05.2016,09:46:06:776,1000205,4,,RG-OS-RED1,DataManager Runtime,F1       Connection 'F1'       connected
255,04.05.2016,09:58:01:770,1000204,4,,RG-OS-RED1,DataManager Runtime,TCP_TDC  Connection 'TCP_TDC'  disconnected
255,04.05.2016,09:58:03:252,1000205,4,,RG-OS-RED1,DataManager Runtime,TCP_TDC  Connection 'TCP_TDC'  connected
255,04.05.2016,10:09:29:425,1000204,4,,RG-OS-RED1,DataManager Runtime,R1       Connection 'R1'       disconnected

WinCC message ID 1000204 is the "connection disconnected" event from DataManager Runtime. 1000205 is the matching "connection connected" event. The pair repeats on roughly a 12-minute cadence in the log sample, which corresponds to the default WinCC S7 keep-alive / supervision cycle and is not a separate fault.

2. Affected System Configuration

3. Decoding the WinCC Status Word 0xFFDF 410E

The WinCC S7 Protocol Suite reports connection-state changes as a 32-bit DWORD. The upper word is the WinCC DSC error class; the lower word is the specific transport error.

The literal text emitted by the channel is "Connectionerror x 'name': Errorcode 0xFFDF 410E!". This is the WinCC S7 transport-layer message and not a SIMATIC TDC or CP51M1 diagnostic buffer entry. The disconnect / reconnect pair (message IDs 1000204 / 1000205) in WinCC_Sys_xx.LOG is the DataManager Runtime reaction to the same event.

4. Network Capture Analysis (Wireshark)

A Wireshark capture on the WinCC server NIC, filtered to the SIMATIC TDC IP and to ISO-on-TCP / S7COMM, shows the following repeating sequence for every failed cycle:

1. WinCC initiates a TPKT/COTP CR (Connection Request) to TDC TCP/102.
2. S7COMM application layer (read / write / cyclic-read) starts with normal TPDU exchanges.
3. At a steady state, a single TPDU sent by WinCC to the TDC is not answered within the local RTO.
4. WinCC retransmits the same TPDU up to seven times, RTO doubling on each retry.
5. After the seventh timeout, WinCC issues TCP RST to abort the connection.
6. The TDC (CP51M1) replies with the expected TPDU, but the answer arrives after the RST.
7. WinCC opens a new connection, the cycle repeats.

Key conclusions from the capture:

• The TDC always responds, so the PLC is not in STOP, has no diagnostic buffer entry, and is not reporting any fault.
• The TCP three-way handshake is never lost; the failure is mid-session, not at connect time.
• The seven-retransmission pattern is the standard Windows TCP retry limit, not a WinCC setting.
• The TDC reply arriving after the RST rules out a TDC-side fault. The TDC processes the request; it is simply slow enough to miss WinCC's local timeout.
• When the Intel NIC is used, the same TDC produces the same response timing, but the WinCC stack does not generate the spurious retransmissions. The difference is therefore not the TDC response time; it is the NIC driver / offload behavior on the DL380p Gen8 Broadcom adapter.

5. Root Cause Hypothesis

The most likely cause is a Broadcom offload feature on the DL380p Gen8 NIC interacting with the SIMATIC TDC's CP51M1 ISO-on-TCP stack in a way that violates WinCC's expected transport timing. The candidate offload features, to be disabled and tested in the order listed, are:

1. TCP/UDP Checksum Offload (IPv4 and IPv6).
2. Large Send Offload v2 (LSO) / TCP Segmentation Offload (TSO).
3. Receive Side Scaling (RSS) and Receive Side Coalescing (RSC / LRO).
4. TCP Offload Engine (TOE) on TOE-capable adapters.
5. Energy Efficient Ethernet (EEE) and Green Ethernet.
6. Adaptive interrupt moderation and the OS power-management "allow NIC to be turned off" flag.

The capture evidence — clean packets on the wire, late TDC reply, identical TDC behavior with the Intel NIC — is consistent with checksum or segmentation offload fragmenting or coalescing COTP TPDUs in a way that the CP51M1 then re-emits. That re-emission falls outside WinCC's RTO budget and WinCC treats the session as dead.

A secondary candidate is the WinCC S7 channel being bound to "TCP/IP (Auto)". If the server carries more than one NIC and Auto binding lands on the Broadcom, the same fix applies. If Auto binding lands on the Intel, the fault does not reproduce. Confirm the binding first.

6. Resolution Procedure

Apply the following steps in order. Test after each step before moving on. Do not roll all changes in at once — that destroys the diagnostic value of each change.

Step 1 — Pin the S7 channel to a specific NIC

1. In WinCC Explorer, open the S7 channel and select the "System Parameters" of the "TCP/IP" driver.
2. Set "Logical Device Name" to a specific adapter, not "TCP/IP (Auto)" — e.g. TCP/IP\Broadcom_NetXtreme_Gigabit_Ethernet.
3. Cross-check with ipconfig /all that the IP chosen for S7 traffic is the one that has the route to the TDC.
4. Restart the WinCC Runtime.

In the reported case, switching from "TCP/IP (Auto)" to a specific device did not resolve the fault when the binding was pinned to the Broadcom device. The fault was reproduced with the binding pinned to the Broadcom, confirming that the binding itself is not the cause. Continue to Step 2.

Step 2 — Confirm "Cycle management by PLC" is OFF

In the WinCC S7 channel system parameters, the "Cycle management by PLC" checkbox must be unchecked. With it checked, the TDC (CP51M1) drives the cycle, and a single missed TPDU is interpreted by WinCC as a connection drop. This was already verified as unchecked in the reported case, so the fault is not caused by this setting. Leave it off.

Step 3 — Disable NIC offload features

On the HP DL380p Gen8 Broadcom adapter, open Device Manager → Broadcom NetXtreme Gigabit Ethernet → Properties → Advanced tab. Set the following to Disabled (or Off):

• IPv4 Checksum Offload: Disabled
• IPv6 Checksum Offload: Disabled
• TCP/UDP Checksum Offload (IPv4): Disabled
• TCP/UDP Checksum Offload (IPv6): Disabled
• Large Send Offload v2 (IPv4): Disabled
• Large Send Offload v2 (IPv6): Disabled
• TCP Segmentation Offload: Disabled
• Receive Side Scaling: Disabled
• Receive Side Coalescing (if listed): Disabled
• Energy Efficient Ethernet: Disabled
• Green Ethernet: Disabled
• Wake on Magic Packet: Disabled
• Wake on Pattern Match: Disabled
• Ultra Low Power Mode: Disabled

On the Power Management tab, uncheck "Allow the computer to turn off this device to save power". Click OK, then disable and re-enable the adapter, or reboot.

Step 4 — Force NIC speed and duplex

On the Broadcom adapter Properties → Advanced → Speed & Duplex, set to 100 Mbps Full Duplex (preferred for ISO-on-TCP / S7COMM segments) or 1.0 Gbps Full Duplex only if the switch port is hard-set the same way. Avoid "Auto Negotiation" if the TDC is connected through an unmanaged or industrial switch. A negotiated drop from 1 Gbps to 100 Mbps mid-stream is a further candidate for the late-reply pattern.

Step 5 — Update or roll back the Broadcom driver

On a DL380p Gen8 running the typical PCS 7 V8.0 SP2 host OS (Windows Server 2008 R2), the relevant driver is the HP-provided Broadcom NetXtreme and NetXtreme II Driver pack, not the generic Microsoft one. Refer to the Siemens Industry Online Support portal and the HP Service Pack for ProLiant (SPP) release notes for the certified NIC driver version.

• Test first with the driver that shipped in the HP Intelligent Provisioning image.
• If the fault appeared after a Windows Update replaced the NIC driver, roll back via Device Manager → Driver → Roll Back Driver.
• Confirm in Device Manager → Details → Hardware Ids that the device is a BCM5719 / BCM5720 / BCM57810 class device. The exact PCI Device ID determines which driver branch applies.

Step 6 — Validate the TDC side (CP51M1)

The CP51M1 firmware in this case is V1.1.4. Confirm the following via D7-SYS V8.0 on the engineering station:

• The CP51M1 is configured as ISO-on-TCP (RFC 1006). CP51M1 does not support S7 native TCP in this firmware.
• The CP51M1's Connection monitoring time is set to a value greater than the WinCC S7 channel watchdog. If the CP51M1 time is shorter, the CP resets the connection first and WinCC sees a partner-initiated close.
• The CP51M1's ISO transport buffer count is at the project maximum. Under-buffering on a busy TDC rack with multiple WinCC partners can stall a single TPDU long enough to trigger the seven-retry cascade.
• The CP51M1's IP, subnet, and routing are correct, and the CP slot reports RUN, not STOP or DEGRADED.

Step 7 — Disable Windows-side TCP offload

Open an elevated command prompt on the WinCC server and run:

netsh int tcp set global autotuninglevel=disabled
netsh int tcp set global rsc=disabled
netsh int tcp set global chimney=disabled
netsh int tcp set global dca=disabled
netsh int tcp set global netdma=disabled
netsh int tcp set global timestamps=disabled

These commands disable Windows-side offload that complements the NIC offload disabled in Step 3.

Step 8 — Apply and verify

Reboot the WinCC server. Confirm the following before re-enabling production traffic:

• ping -t <TDC IP> runs for 30 minutes with zero loss.
• Wireshark capture of one full WinCC boot-to-S7-connection cycle shows zero TCP retransmissions.
• WinCC_Sys_xx.LOG shows no 1000204 / 1000205 pairs in a 24-hour window.
• SIMATIC_S7_Protocol_Suite_xx.LOG shows no "Errorcode 0xFFDF 410E" lines in a 24-hour window.

7. Broadcom NIC Driver and Registry Settings

If the Advanced-tab toggles in Device Manager are not sufficient (typical on older HP customized driver packs that hide options), the same controls are exposed in the registry. Back up the registry before editing.

Registry path: HKLM\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318}\####, where #### is the instance number of the Broadcom NIC. Confirm with the DriverDesc value that it reads "Broadcom NetXtreme Gigabit Ethernet" or similar.

Restart the network adapter (Disable, then Enable) or reboot for the changes to take effect. Verify the new state with Get-NetAdapterAdvancedProperty -Name "*" in PowerShell.

8. HP ProLiant DL380p Gen8 Server-Side Settings

Beyond the NIC, the following HP ProLiant Gen8 settings can also affect S7 traffic:

• HP Intelligent Provisioning → Agentless Management Service (AMS): keep enabled, but exclude the S7 NIC from agentless monitoring. AMS polls the NIC and can inject latency that triggers the seven-retry cascade on the WinCC side.
• HP iLO 4 Management Network: bind iLO to the dedicated iLO port, not to a shared NIC. iLO sharing on the Broadcom port competes with S7 traffic.
• HP Power Regulator: set to "OS Control Mode" rather than "HP Static Low Power Mode" to avoid CPU C-state throttling that delays the WinCC S7 process.
• HP Network Configuration Utility (NCU): if installed, set the Broadcom port profile to "Throughput" rather than "Power Save".
• BIOS: disable "Intel TXT Support" only if virtualized; otherwise no change required for this fault.
• Windows Power Options: select the "High performance" power plan. The "Balanced" plan enables PCI Express ASPM, which can hold off the NIC.

9. SIMATIC TDC and CP51M1 Configuration

CP51M1 module details:

• Module: SIMATIC TDC CP51M1, the Industrial Ethernet / IP communication module for the SIMATIC TDC rack.
• Firmware: V1.1.4 in this case. Verify against the SIMATIC TDC CPU 551 hardware version (6DD1600-0BA2) and the D7-SYS V8.0 option package before changing.
• Configuration tool: D7-SYS V8.0 with the "SIMATIC TDC" option package installed.

Configuration checks to perform in D7-SYS:

1. In the D7-SYS project tree, open the CP51M1 module under the TDC rack.
2. Open the "Connection" or "Transport" configuration. Confirm the connection type matches the WinCC S7 channel: for a WinCC S7 channel on "TCP/IP", use ISO-on-TCP (RFC 1006) on the CP51M1. S7 native TCP is not supported on the CP51M1 in firmware V1.1.4.
3. Confirm the connection is "Active" or "Passive" consistent with the WinCC side. In PCS 7 V8.0 SP2, WinCC is the Active partner and the CP51M1 is Passive.
4. Open the "Diagnostic" tab. If any "Transport buffer full" or "Connection aborted" event appears during the time the 0xFFDF 410E error is logged, the TDC is shedding load and the fix is to increase the CP51M1 transport buffer count or split the connection across two CPs.
5. Cross-check the CP51M1 firmware V1.1.4 against the Siemens compatibility list for PCS 7 V8.0 SP2. CP51M1 firmware updates are released as HSP files in the Siemens HSP download area.

The WinCC side channel configuration is set up in the Connections editor of the TIA Portal / WinCC configuration, with the connection parameter set to TCP/IP for S7-1200/1500-class panels. For SIMATIC TDC, the equivalent parameters live in the WinCC Channel "TCP/IP" system parameters, not in the TIA Portal connections editor. Refer to the TIA Portal documentation for the general pattern of TCP/IP connection parameters for SIMATIC S7 PLCs at docs.tia.siemens.cloud.

10. Verification Procedure

After applying the fix, run the following sequence:

1. Open the WinCC S7 channel diagnostics (right-click the channel → "System Parameters" → "Diagnostics").
2. Confirm zero "Errorcode 0xFFDF 410E" entries in a 24-hour window.
3. Open SIMATIC_S7_Protocol_Suite_xx.LOG and confirm zero ERROR entries containing "0xFFDF 410E".
4. Open WinCC_Sys_xx.LOG and confirm no "1000204 ... disconnected" followed by "1000205 ... connected" pairs.
5. Run Wireshark on the WinCC server for 30 minutes and confirm zero TCP retransmissions, zero RST, and zero zero-window events.
6. From the engineering station, run a continuous S7 connection test (Start → SIMATIC Manager → "S7 Connection Diagnostics" or equivalent) and confirm all configured partners show "Established" and remain so.
7. On the TDC, read the CP51M1 diagnostic buffer via D7-SYS V8.0 → CP51M1 → Online → Diagnostic Buffer. Confirm no "Connection aborted by partner" entries during the test window.

If any of the above still shows a fault after Step 3 + Step 5 + Step 7 of the resolution procedure, suspect a physical-layer issue (cable, switch, SFP if used) and replace it. Capture with Wireshark on a hub or tap inserted between the server and the switch to confirm the late-reply pattern is still present and is not a switch-side buffer drop.

11. Prevention and Monitoring

Long-term measures for a PCS 7 / WinCC / SIMATIC TDC site running on Broadcom-equipped HP ProLiant Gen8 servers:

• Add a Wireshark rolling capture (1 GB ring buffer) on the WinCC server S7 NIC and archive it weekly. Wireshark cannot diagnose 0xFFDF 410E directly but is the only tool that proves whether the NIC or the partner is the source of the spurious retransmissions.
• Schedule a quarterly review of the Broadcom driver version against the latest HP Service Pack for ProLiant (SPP). HP bundles the NIC driver in the SPP, and updates there often fix offload regressions.
• Document the exact Broadcom Advanced-tab settings in the WinCC server build documentation. A Windows Update can silently re-enable offload values to the driver default.
• Configure a SIMATIC PCS 7 OS project "Connection status" alarm that fires on any 1000204 event. This gives operations the first sign of regression and avoids a silent quality-of-service drop.
• Maintain a spare Intel NIC (or a small Intel USB-to-Ethernet adapter) preconfigured on the bench. It is a known-good fallback while the Broadcom issue is being analyzed.

12. Troubleshooting Matrix