1. Problem Definition
The SIMATIC ET 200S IM 151-8 PN/DP CPU (order number 6ES7151-8AB00-0AB0 and the successor 6ES7151-8AB01-0AB0) is a bit-modular, distributed I/O station with an integrated PROFINET interface and an additional PROFIBUS DP master/slave port. Because it ships with an empty IP stack (0.0.0.0/0.0.0.0 by default), the controller must be commissioned through STEP 7 V5.x (Simatic Manager) before any TCP-based service (S7 communication, RFC 1006, online diagnostics, download) will answer.
The reported failure mode is reproducible and well-known in field service:
- Hardware is wired: PROFINET port of the IM151-8 connected to the engineering PC's NIC with a standard Cat5/Cat6 patch cord (or through an unmanaged switch).
- HW Config is opened in Simatic Manager, the IM151-8 PN/DP object is inserted, and an IP address plus PROFINET device name are assigned in the object's Properties > PROFINET Interface dialog.
- The configuration is saved and translated, but the subsequent PLC > Download to Target System action fails with "Connection to target system could not be established" or "No online connection available".
- PLC > Edit Ethernet Node > Browse returns an empty list.
- A
ping <CPU IP>from the Windows command prompt returns Request timed out or Destination host unreachable.
Because the ping layer (ICMP) is the very first protocol that must work, a negative ping rules out STEP 7 itself as the failing component. The fault sits below STEP 7, on the Windows TCP/IP stack, the NIC driver, the physical link, or a third-party packet filter.
2. Root Cause Analysis
Connection failures of the IM151-8 PN/DP can be grouped into five root-cause families, listed in order of how frequently they are observed in field service:
| # | Root Cause | Symptom | Quick Test |
|---|---|---|---|
| 1 | Host-based packet filter (Symantec Endpoint Protection, McAfee, Kaspersky, Windows Defender Firewall, third-party HIDS) blocks ISO-on-TCP / TCP port 102 (RFC 1006) and/or ICMPv4 | Ping fails; STEP 7 Browse returns nothing; Symantec Endpoint Protection or equivalent logs a dropped packet | Temporarily disable the filter, retest ping |
| 2 | PG/PC interface assigned in the Windows Control Panel — Set PG/PC Interface — points to the wrong NIC, a disabled virtual adapter, or a non-existent TAP driver | Browse returns nothing; download hangs; STEP 7 complains "Online: The interface is not accessible" | Set the access point S7ONLINE to TCP/IP <correct NIC> |
| 3 | IP subnet mismatch — PC and CPU on different subnets, no default gateway, or duplicate IP on another host | Ping fails with Destination host unreachable; ARP shows no entry for the CPU | Run ipconfig /all, confirm ping 255.255.255.255 from a helper host |
| 4 | PROFINET device name not assigned / not in the project; PROFINET topology mismatch; PN cable on the wrong port (X1 vs X2) of the IM151-8 | CPU powers up, link LED is on, but "Accessible Nodes" returns nothing and the CPU's SF/DIAG LED is solid red | Re-assign the PROFINET name in HW Config; restart the CPU |
| 5 | Damaged patch cord, switch port in wrong VLAN, or NIC power-management (Energy Efficient Ethernet) putting the link to sleep | Link LED off, intermittent link, ping fails half the time | Replace the cable; disable EEE in the NIC advanced properties; force NIC speed/duplex to 100 Mbit/s full duplex |
The most frequently missed root cause in the field is the first one: a host-based security suite that drops outbound RFC 1006 / TCP 102 traffic without surfacing a Windows Security alert. The documented field case in this article was caused by Symantec Endpoint Protection, which silently applied a default-deny rule to the engineering NIC.
3. Pre-flight Checklist
- Verify the CPU is powered and the LINK LED on the PROFINET port (X1 P1) is lit. No link » no software remedy will work.
- Confirm the engineering PC NIC link LED is also lit at the same speed/duplex. Mismatched link speeds (e.g. one side at 10 Mbit/s half duplex) routinely break PROFINET discovery.
- Open Control Panel > Set PG/PC Interface and record which access point is bound to which NIC. Note the access point names used for online work:
S7ONLINE(TCP/IP) andS7ONLINE_STEP7for newer STEP 7 builds. - Confirm the PC's IP address, mask, and gateway:
ipconfig /all netsh interface ip show address "Ethernet"
- From the PC command line, ping the default gateway and a known-good host on the same subnet to verify basic Layer 3 connectivity.
- Open Windows Defender Firewall with Advanced Security (or the corporate replacement) and note which profile is active: Domain, Private, or Public. Public profile will block almost everything by default.
4. Step-by-Step Diagnostic Procedure
4.1 Verify the CPU Is Reachable at Layer 3
- In Simatic Manager, choose PLC > Edit Ethernet Node.
- Click Browse. STEP 7 sends a DCP Multicast (UDP port 34964, destination 01:0E:CF:00:00:00). If the IM151-8 replies, it appears in the list with its MAC address, IP, and device name (default:
im151-8). - If Browse returns nothing, manually type the assigned IP into the IP address field and click Accessible Nodes after setting S7ONLINE to TCP/IP.
- From a Windows command line, send a continuous ping while you press the CPU's MRES button to force a reboot:
ping -t 192.168.0.10
Watching the reply during a reboot is the fastest way to confirm ARP is resolving the CPU's MAC.
4.2 Eliminate Host-Based Security Filters
- Open the security suite (Symantec Endpoint Protection in the documented case) and navigate to the Exceptions / Firewall Policy section.
- Add an inbound and outbound rule for the following ports and protocols used by STEP 7 and the IM151-8:
Port Protocol Service 102 TCP (RFC 1006 / ISO-on-TCP) S7 communication, online download, diagnostics 161 / 162 UDP SNMP (used by STEP 7 topology editor) 34964 UDP PROFINET DCP discovery 49152–65535 TCP / UDP PROFINET RPC, LLDP, MRP (dynamic range) ICMPv4 Echo ICMP Ping diagnostic - If your corporate policy does not allow static exceptions, add
S7DOS.EXE,S7OTBXSX.EXE, andS7SCANBX.EXE(the STEP 7 online executables, located in%ProgramFiles%\Siemens\Automation\SIMATIC_..\S7BIN) to the application-based allow list. - For a fast triage, set the firewall to Allow all traffic for the engineering NIC, retest, and re-tighten later.
4.3 Re-create a Clean PG/PC Interface Assignment
- Close Simatic Manager completely.
- Open Control Panel > Set PG/PC Interface (or run
SetPgPcInterface.exefromSiemens\Automation\SIMATIC_..\S7BIN). - For the access point S7ONLINE, choose TCP/IP → <physical NIC>. Avoid virtual adapters (Hyper-V, VMware, VPN TAP) unless the CPU actually sits behind them.
- Click Diagnostics to confirm the chosen NIC responds. The Diagnostics dialog sends an ARP and reports the MAC and link speed.
- Re-launch Simatic Manager and retry PLC > Edit Ethernet Node > Browse.
4.4 Re-assign the IP Address and PROFINET Name
- Open the project in Simatic Manager and double-click the IM151-8 PN/DP station to launch HW Config.
- Select the IM151-8 in the rack and open Object Properties > PROFINET Interface > Ethernet.
- Enter the IP address, subnet mask, and (if needed) router. Do not leave the IP set to
0.0.0.0— the CPU will not respond to ARP without a valid IP. - Switch to the PROFINET tab and assign a unique device name. The default
im151-8is acceptable for a single-CPU subnet, but a name collision will cause a startup fault. - Save and translate the project (Station > Save and Compile).
- With the PG/PC interface set to TCP/IP, choose PLC > Download to Target System. STEP 7 will offer to overwrite the IP and PROFINET name on the device; confirm.
4.5 Verify with SIMATIC Automation Tool (Optional)
The free SIMATIC Automation Tool (SAT) can scan the Ethernet subnet, set IPs and PROFINET names on multiple devices, and reset factory defaults. Use it as a second-opinion tool when Simatic Manager Browse keeps returning nothing.
5. Hardware and Firmware Reference
| Parameter | IM 151-8 PN/DP (6ES7151-8AB00-0AB0) | IM 151-8 PN/DP (6ES7151-8AB01-0AB0) |
|---|---|---|
| Firmware range | V1.0 – V3.2 | V4.0 – V4.4 |
| PROFINET ports | 2 × RJ45 (X1 P1, X1 P2), 100 Mbit/s | 2 × RJ45, 100 Mbit/s, integrated switch |
| PROFIBUS port | 1 × RS485 (X2), DP master/slave, 12 Mbit/s | 1 × RS485, DP master/slave, 12 Mbit/s |
| Default IP | 0.0.0.0 | 0.0.0.0 |
| Default PROFINET name | im151-8 | im151-8 |
| Memory (work / load) | 128 KB / 2 MB | 256 KB / 4 MB |
| STEP 7 version | V5.4 SP5 or higher; V5.6 recommended | V5.5 SP4 or higher; V5.6 / V5.7 |
| TIA Portal support | From V13 SP1 Update 5 (as PROFINET device) | From V14 SP1 |
Cross-reference the actual order number on the front of the module against the Siemens Product Support > 6ES7151-8AB manual set. Mismatched firmware is a common cause of Browse returning nothing on a freshly purchased CPU — the module ships with V1.0 firmware in rare cases, and old STEP 7 V5.3 libraries will not talk to it.
6. Network Troubleshooting Matrix
| Symptom | First Check | Second Check | Resolution |
|---|---|---|---|
| Ping fails, link LED on | Symantec / McAfee / Windows Firewall | NIC driver — EEE / energy saving | Disable firewall, add S7ONLINE exception, disable Energy Efficient Ethernet in NIC advanced properties |
| Ping fails, no link LED | Patch cord, switch port | NIC speed/duplex forced to 10 Mbit/s | Replace cable, force 100 Mbit/s FD, test direct NIC-to-NIC |
| Browse returns empty, ping OK | PG/PC interface bound to wrong NIC | PROFINET name mismatch | Reassign S7ONLINE → TCP/IP <NIC>, assign device name in HW Config |
| Download starts, aborts at 30% | MRP topology loop | Translation error in HW Config | Disable MRP for first commissioning, recompile and download |
| SF LED solid red, BF red | PROFINET name missing | Duplicate IP on the network | Use SAT or Edit Ethernet Node to assign name and unique IP |
| CPU in STOP, MAINT yellow blinking | Firmware update pending | Configuration mismatch after hardware swap | Perform PLC > Update Firmware or Memory Reset from MRES |
7. STEP 7 Error Messages and Their Meaning
| STEP 7 Message | Hex / Code | Meaning | Action |
|---|---|---|---|
| "The online interface is inaccessible" | 0x0110 / W#16#0110 | PG/PC interface not assigned or assigned NIC down | Re-run Set PG/PC Interface |
| "Target system could not be reached" | 0x0130 / W#16#0130 | No ARP response from CPU IP | Ping, check firewall |
| "Connection was broken" | 0x0330 / W#16#0330 | TCP 102 reset during download | Reduce parallel network traffic, disable antivirus real-time scan on S7BIN |
| "Different CPU type in target system" | 0x0E02 / W#16#0E02 | HW Config does not match the connected CPU | Re-detect CPU with Accessible Nodes |
| "PROFINET device name is invalid" | 0xE0FF | Device name not downloaded | Re-assign in Edit Ethernet Node |
8. Field-Proven Workarounds
When corporate policy prevents disabling a security suite, the following workarounds have been validated on the IM151-8 platform:
- USB-to-Ethernet adapter on a dedicated subnet: Bind S7ONLINE to a dongle NIC that is excluded from the corporate firewall. Most endpoint protection suites do not apply rules to a NIC that is not in the managed network profile.
- Out-of-band commissioning PC: Use a non-domain-joined laptop with Windows Firewall set to Off for the commissioning session only. Re-join the domain after the project is downloaded.
- Repair the STEP 7 install: If the firewall was recently added or upgraded, the S7DOS service may have lost its firewall rule. Run Setup > Repair from the STEP 7 installation media; the install routine re-registers firewall exceptions for S7BIN executables.
-
Set a static ARP entry: As a last resort, pin the CPU's MAC to its IP in the PC's ARP table to force Layer 2 resolution while you triage the firewall:
arp -s 192.168.0.10 00-0E-8C-XX-XX-XX
9. Verification Checklist
- From the engineering PC,
ping -t <CPU IP>returns 0% packet loss for at least 60 seconds. - In Simatic Manager, PLC > Edit Ethernet Node > Browse lists the IM151-8 with correct MAC, IP, and PROFINET name.
- PLC > Accessible Nodes shows the CPU with a green status icon.
- PLC > Download to Target System completes and STEP 7 prompts "Do you want to start the CPU?" — the CPU is now online.
- The CPU's RUN LED is solid green and the SF, BF, and MAINT LEDs are off.
- Online > Monitor/Modify works on a known tag (e.g.
OB1_Main_TimeOfDay).
10. Related SIMATIC Platforms
The same diagnostic flow applies to other PROFINET-equipped ET 200 CPUs that share the IM151-8 family:
- IM 151-8F PN/DP (6ES7151-8FB00-0AB0) — fail-safe variant; identical networking behaviour, plus F-CPU signature check on download.
- IM 154-8 PN/DP (6ES7154-8AB00-0AB0) — ET 200pro form factor, same PROFINET stack, same firewall exposure.
- ET 200S CPU family and the newer ET 200SP CPU 1510SP-1 PN (6ES7510-1DJ01-0AB0) — identical troubleshooting path, but uses TIA Portal instead of Simatic Manager.
When migrating to TIA Portal, the equivalent of Edit Ethernet Node is Online > Accessible Devices. The same port-exception list (TCP 102, UDP 34964, UDP 161/162) applies because both STEP 7 and TIA Portal use the same PROFINET and S7 communication stack.
11. Safety and Operational Notes
Why does "Edit Ethernet Node > Browse" return an empty list even though the CPU is on the same switch?
The Browse function uses PROFINET DCP (UDP 34964). If the Windows firewall, Symantec Endpoint Protection, or a similar host-based filter is blocking this port, the CPU never receives the discovery request. Add UDP 34964 and TCP 102 to the firewall exception list, and Browse will populate immediately.
I can ping the IM151-8 from the PC, but STEP 7 still fails to download. What is wrong?
Ping uses ICMP, which most security suites allow by default. STEP 7 download uses TCP port 102 (RFC 1006 / ISO-on-TCP). Confirm with telnet <CPU IP> 102; if the connection is refused, a firewall is dropping the TCP handshake. Allow S7DOS.EXE and S7OTBXSX.EXE in the security suite's application rules.
The IM151-8 has a red SF LED after power-up. Does this mean it is broken?
No. A solid SF LED on a brand-new IM151-8 almost always means the PROFINET device name has not been downloaded. Use PLC > Edit Ethernet Node or the SIMATIC Automation Tool to assign a unique name, then power-cycle the module. The SF LED should clear and the RUN LED should come on steady green.
Can I assign the IP address directly on the CPU without STEP 7?
Yes. The IM151-8 supports the SIMATIC Automation Tool (SAT) and the PRONETA commissioning tool, both of which can write the IP and PROFINET name to the device's flash using only the DCP protocol. SAT is available free of charge from Siemens Support entry 109767289.
Will TIA Portal solve the firewall problem automatically?
No. TIA Portal and Simatic Manager use the same PROFINET and S7 communication libraries, so the same firewall rules apply. On a fresh Windows 10/11 install, Windows Defender Firewall may block the discovery by default; explicitly allow the TIA Portal executables or temporarily disable the firewall for the engineering NIC during commissioning.