C135 PCS 7 (PCS7)
6C
6 Cielo Ciencia y Tecnología
·Publicada en C135 PCS 7 (PCS7)

Troubleshooting SNMP Device Not Answering on Clients in PCS 7 Maintenance Station

Troubleshooting SNMP Device Not Answering on Clients in PCS 7 Maintenance Station

In PCS 7 Maintenance Station (MS), OS Clients display a red wrench and the alarm 'SNMP device is not answering' when the Windows SNMP Service on the client computers is misconfigured, blocked by Windows Firewall, or restricted by host security filters. Although the Windows SNMP component is installed, clients reject SNMP queries unless the accepted community name (e.g., 'public') is explicitly configured with READ ONLY rights, the Maintenance Station OPC Server IP is added to the accepted host list, and inbound UDP port 161 is open.

Table of Contents

SNMP Architecture in PCS 7 Maintenance Station

The SIMATIC PCS 7 Maintenance Station (MS) provides comprehensive plant asset management, visualizing the diagnostic states of field instrumentation, automation controllers, SCALANCE network switches, and computer nodes (ES, OS Servers, and OS Clients).

For PC station monitoring (ES/OS/Clients), the Maintenance Station utilizes the SIMATIC NET SNMP OPC Server:
1. The OPC Server polls network nodes cyclically using the Simple Network Management Protocol (SNMP v1/v2c) over UDP port 161.
2. Windows operating systems host an internal SNMP Service providing Management Information Base (MIB-II) parameters, such as hard disk space, CPU utilization, network adapter status, and operating system runtimes.
3. In SIMATIC Manager Component View, the SNMP device list of the OPC Server defines monitored target IP addresses.
4. If an OS Client fails to respond to SNMP polling within the configured timeout window, the Maintenance Station generates a process alarm SNMP device is not answering and displays a red maintenance wrench across the client asset icon.

Root Causes of SNMP Communication Failures on OS Clients

When only one client visualizes successfully while seven identical clients fail with red maintenance wrenches, the issue invariably stems from localized Windows service or firewall settings rather than PCS 7 project engineering:

  1. Missing or Mismatched SNMP Community Name: The Windows SNMP service requires a configured community string (typically public). If the community string is absent, mistyped, or set with incorrect rights (e.g., "None" instead of "READ ONLY"), the agent discards queries.
  2. Restricted Host Access Security Rules: Under the Security tab of the Windows SNMP service, selecting "Accept SNMP packets from these hosts" blocks all traffic unless the exact IP address of the Maintenance Station OPC Server (and redundant partner) is enumerated in the authorized host table.
  3. Windows Firewall Blocking UDP Port 161: Even when the SNMP feature is installed, Windows Firewall frequently blocks inbound UDP traffic on port 161 on private/domain network profiles.
  4. Unstarted SNMP Service: The Windows SNMP service startup type may be set to Manual rather than Automatic, remaining dormant after a reboot.

Step-by-Step Configuration of Client SNMP Services

On each failing OS Client machine, execute the following administrative configuration:

  1. Verify Windows SNMP Service Configuration:
    * Open Windows Services (services.msc).
    * Double-click SNMP Service. Set the Startup type to Automatic.
    * Navigate to the Security tab.
  2. Configure Community Names and Host Security:
    * In the Accepted community names box, click Add.
    * Set Community Rights to READ ONLY and Community Name to public (case-sensitive; must match the community string configured in the PCS 7 OPC Server).
    * Under Accept SNMP packets:
    • Either select Accept SNMP packets from any host (recommended in isolated industrial LANs), OR
    • Select Accept SNMP packets from these hosts and add the IP addresses of the Maintenance Station, OS Servers, and Engineering Station.
  3. Configure Windows Firewall Inbound Rules:
    * Open Windows Defender Firewall with Advanced Security.
    * Under Inbound Rules, verify that the rule SNMP Service (UDP In) is enabled for the Domain and Private network profiles.
    * If creating a custom rule, allow inbound UDP Port 161.
  4. Restart the SNMP Agent:
    * In Windows Services, right-click SNMP Service and select Restart.
    * Ensure that the dependent SNMP Trap service is also configured and running if traps are utilized.

Verification

  • On the Maintenance Station PC, open Command Prompt and test network reachability using an SNMP walk utility (or the Siemens SNMP test tool snmptool.exe or snmpwalk -v 2c -c public <Client_IP>).
  • In WinCC Runtime on the Maintenance Station, open the Diagnostics -> PC Stations screen.
  • Confirm that the red maintenance wrench clears on the OS Client icons, transitioning to a healthy gray or green status icon.
  • Open the Alarm Control and verify that the alarm SNMP device is not answering for each client is automatically cleared (gone).

Limitations and Operational Precautions

  • SNMP v1 and v2c transmit community strings in cleartext across the network. Ensure that industrial Terminal Buses are isolated from corporate enterprise networks.
  • Do not configure community rights as READ WRITE on client machines unless remote administrative configuration via SNMP is explicitly required by IT security policies.
  • When using redundant Maintenance Stations, both MS Server IP addresses must be registered in the client's accepted host list.

Engineer FAQ

  • Why did one client work while seven clients failed with the same configuration?
    The working client likely had its firewall rule enabled by another software installer, had the default community name already populated, or belonged to a different network profile (Domain vs. Public) in Windows.
  • Does installing the Windows SNMP component automatically start the service?
    No. On many Windows Server and Windows 10/11 Enterprise builds, installing the optional feature leaves the service stopped or requires manual configuration of community strings before it responds to network queries.
  • Can I monitor client hard drive capacity through Maintenance Station SNMP?
    Yes. The SIMATIC NET SNMP OPC Server queries standard Host Resources MIB (hrStorage) to report drive capacity and warn operators before disks fill up.

Technical References

  • SIMATIC PCS 7 Maintenance Station Operating Manual (A5E41356272-AA).
  • SIMATIC NET PC Software - Industrial Communication with SNMP OPC Server Manual.
  • Siemens Industry Online Support Entry ID 109801081: Configuring Asset Management and SNMP in PCS 7.

Related Articles

Related Tags

PCS 7, Maintenance Station, SNMP, OS Client, OPC Server, Diagnostics, Windows Firewall, Asset Management

20 respuestas