Fix SIMOTION D455-2 Web Server Connection Refused Error

1. Problem Overview

SIMOTION D455-2 controllers running firmware V5.6 SP1 HF4 in combination with the technology package SIMOTION SCOUT TIA V5.6.1.0 and TIA Portal V19 may refuse HTTP/S connections to the integrated SIMOTION IT Web server. Browsers report ERR_CONNECTION_REFUSED in Chrome and Can't connect securely in Microsoft Edge, even when the controller responds to ICMP echo (ping) and the Web server is explicitly enabled in SCOUT TIA. The root cause is typically a corrupted or inconsistently written UserDataBase.xml on the controller's CompactFlash card, not a TCP/IP routing or firewall problem.

This article documents the exact failure mode observed on part number 6AU1455-2AD00-0AA2 (D455-2 redesign), the diagnostic path used to isolate the Web server from the user administration, and the corrective procedure to rebuild UserDataBase.xml without re-flashing the controller firmware. The procedure preserves the runtime application and the existing project on the controller; only the user accounts and passwords are reset.

2. Affected Hardware, Firmware, and Tool Versions

The following combinations have been observed in the field to exhibit the symptom. Confirm whether the installation matches before applying the repair procedure.

The same symptom can also occur on:

• D4x5-2 variants: D425-2, D435-2, D445-2, D455-2 on the same firmware family.
• Older CPU revisions running a V5.6 project that has been upgraded from a pre-V4.4 firmware without preserving the user database.
• Replacement CompactFlash cards that have been swapped between controllers without re-running the user administration wizard.

3. Symptoms and Initial Diagnostics

Confirm the symptom set matches before opening the controller. Each check below takes seconds and rules out adjacent failure modes.

1. Ping succeeds: The host responds to ping <IP>. This proves L2/L3 reachability and confirms the controller is fully booted (SINAMICS integrated is up).
2. Web server is enabled in SCOUT TIA: In the project tree, right-click the D455-2 device → Properties → Web server → "Activate Web server" is checked. Port 80 (HTTP) and/or 443 (HTTPS) is configured.
3. Browser returns "connection refused": Chrome displays This site can't be reached — <IP> refused to connect. ERR_CONNECTION_REFUSED; Edge displays Can't connect securely to <IP>. The error is immediate, not a timeout.
4. FTP/Telnet also fail: Because FTP and Telnet are routed through the same user administration database, attempts with FileZilla or PuTTY on TCP/21 and TCP/23 fail with similar "connection refused" or "login failure" symptoms. This is a strong indicator the user DB is the failure point.
5. SCOUT TIA online connection succeeds: The engineering tool can still go online with the controller via the configured PROFINET/Industrial Ethernet interface because SCOUT uses its own S7-style channel, not the Web server HTTP/S stack.
6. Diagnostic buffer entries: Read the controller diagnostic buffer (SCOUT TIA online → controller → diagnostic buffer). Look for entries containing "WEB", "USER", or "XML" — these confirm the user database parse failure at boot.

4. SIMOTION IT Web Server Architecture

The SIMOTION IT Web server is an embedded HTTP/S daemon running inside the SIMOTION runtime. It serves diagnostic, parameter, and trace data to a standard browser. As of SIMOTION V4.4, the daemon is protected by a multi-level security concept that separates the transport (HTTP/S) from the user administration (FTP/Telnet/Web).

4.1 Service Map

4.2 Request Flow

When a browser opens https://<controller-ip>/, the request follows this path:

1. TCP SYN arrives on port 80 or 443 from the engineering station.
2. The SIMOTION IT daemon accepts the socket only if the user database parses correctly.
3. The daemon maps the request URI to a handler based on the configured security level (Low, Normal, High).
4. The handler authenticates the user against UserDataBase.xml.
5. The diagnostic page is rendered from runtime data and returned over the socket.

If step 2 fails because UserDataBase.xml is unreadable or malformed, the daemon does not bind the listening socket. The TCP stack responds to inbound SYN with RST, which the browser reports as connection refused. There is no HTTP response and no SSL handshake because the socket never opens.

4.3 Default Ports and Redirect Behavior

5. SIMOTION IT Security Concept (V4.4 and Later)

As of SIMOTION V4.4, the SIMOTION IT Web server is governed by a three-level security model. The active level is shown on the Web server home page and controls which diagnostic data is exposed without authentication. The model is fully described in the SIMOTION IT Diagnostics and Configuration Diagnostics Manual, section "Security concept".

The security level is configured in SCOUT TIA and stored in the project; it is written to the controller together with the user database during project download. If the active project and the user database on the card become inconsistent (for example, after a partial download, a card swap, or a downgrade), the daemon may still start, but authentication fails — or, in the failure mode described here — the daemon refuses to start at all.

Three additional security controls interact with the Web server:

• Password complexity rules: At security level High, passwords must be at least 8 characters and contain mixed case, digits, and a special character. At level Normal, a minimum length of 6 characters is enforced.
• Session timeout: The Web server enforces an idle timeout configurable per security level. Timeouts shorter than expected can be a sign of a misconfigured project, not corruption.
• HTTPS certificate: The default certificate is self-signed. Browsers warn on first access; click-through is acceptable for commissioning. For production, replace with a CA-signed certificate from the certificate store.

Detailed information is in the SIMOTION IT Diagnostics and Configuration Diagnostics Manual (entry 109963298), section "Security concept" and "Activating communications services in SCOUT TIA" (section 3.3).

6. Root Cause — UserDataBase.xml Corruption

UserDataBase.xml is the XML file that stores all user accounts, password hashes, and per-service permissions for the SIMOTION IT Web server, FTP, and Telnet services. On a D4x5-2 the file resides on the CompactFlash card; the canonical path on V5.6 firmware is:

USER/SIMOTION/UserDataBase.xml
USER/SIMOTION/UserDataBase.xml.bak    (optional auto-backup)

6.1 File Structure

A healthy UserDataBase.xml follows the SIMOTION user database schema. A minimal valid example with one admin account follows the pattern below. The exact attribute set, schema version, and password hash algorithm are firmware-dependent — a file written by V5.6 is not always compatible with V4.x firmware and vice versa.

<?xml version="1.0" encoding="UTF-8"?>
<UserDatabase version="1.0">
  <User name="admin" role="Administrator">
    <PasswordHash algorithm="SHA-256">...</PasswordHash>
    <Services>
      <Service name="WEB" enabled="true"/>
      <Service name="FTP" enabled="false"/>
      <Service name="TELNET" enabled="false"/>
    </Services>
  </User>
</UserDatabase>

6.2 Corruption Sources

A corrupted UserDataBase.xml can be produced by any of the following events:

• Power loss during a project download while the user database is being rewritten.
• Removal of the CompactFlash card while the runtime is writing diagnostic counters.
• Replacing a card from a different D4x5-2 without re-running the user administration wizard.
• Manually editing the file (for example, to add users) and introducing an XML schema violation.
• Mixed-version downgrade where the runtime expects V5.x schema but finds a V4.x file (or vice versa).
• Interruption of the write by an E-stop or 24 V DC rail dip during a SCOUT TIA → controller download.
• File system corruption from an ageing or out-of-spec CF card.

The runtime detects the corruption at boot when it tries to parse the file. Rather than fall back to an empty user set, the SIMOTION IT daemon terminates. This produces the "connection refused" symptom observed by the browser. The diagnostic buffer logs entries such as WEB-SERVER USER DB PARSE ERROR, XML schema mismatch, or USER DB: file unreadable; the exact text varies by firmware.

7. Pre-Repair Validation Checklist

Before rebuilding the user database, complete this checklist. Each item either confirms the repair path or diverts to a different procedure.

1. Confirm the controller is in Stop or Stop with ramp-down state, depending on whether the process permits a full stop. User database replacement requires the Web server subsystem to be stopped.
2. Verify TIA Portal V19 and SCOUT TIA V5.6.1.0 are both installed and licensed on the engineering station. Open TIA Portal → Help → Installed software to confirm version.
3. Verify the project on the engineering station matches the firmware on the controller. In SCOUT TIA, right-click the D455-2 → Online → Compare offline/online. Differences in the Web server subtree are a red flag.
4. Export the current project as a TIA Portal archive (.zap19) for rollback safety. Store it in the project repository, not on the engineering station desktop.
5. Read the diagnostic buffer via SCOUT TIA (online → controller → diagnostic buffer). Look for entries containing "WEB", "USER", or "XML". Take a screenshot for the support bundle.
6. Open a Windows command prompt and run telnet <controller-ip> 21 and telnet <controller-ip> 23. Both should return "connection refused" if the user DB is the failure point.
7. Run curl -v http://<controller-ip> --max-time 5 from the engineering station to capture the exact TCP error (RST vs. timeout) for the support bundle.
8. Check the controller's diagnostic LEDs: SF (system fault) and BF (bus fault) should be off; only the RUN LED should be solid green for the Web server symptom. Any other combination indicates a different fault.

8. Step-by-Step Repair Procedure

The repair rebuilds UserDataBase.xml on the controller by re-running the user administration download from SCOUT TIA. The original user accounts are lost unless a backup exists, so plan for credential reset. Allow a maintenance window of approximately 15 minutes.

8.1 Back up the current card contents (best effort)

1. Power down the D455-2. Wait for the CF card access LED to extinguish (typically 10 seconds).
2. Remove the CompactFlash card using an industrial-grade CF card reader.
3. Copy the entire card contents to a folder named D4552_backup_YYYYMMDD. Pay special attention to USER/SIMOTION/UserDataBase.xml; copy it even if it appears truncated or zero-byte.
4. Insert the card back into the controller and power up. Wait for the RUN LED to be solid green before continuing.

8.2 Delete the corrupted user database on the card

1. Open SCOUT TIA V5.6.1.0 with the project matching the controller firmware.
2. Go online with the controller via Online → Connect to target system.
3. Right-click the D455-2 → Web server → User administration.
4. The dialog will report that the user database cannot be read. Note the exact message text and click OK.
5. Navigate to Project → Web server → Reset user database on target system. Confirm the prompt. This deletes UserDataBase.xml on the card and re-creates a minimal file with only the admin account.

8.3 Re-download the user administration from SCOUT TIA

1. While still online, open Web server → User administration.
2. Re-create the required user accounts and assign the appropriate roles (read-only, diagnostic, administrator). Use passwords that comply with the active security level — under security level High, weak passwords are rejected with a dialog.
3. Click Download to target system. The progress indicator should reach 100% without error. A failure here usually indicates a stale project; reload the project and retry.
4. After successful download, the controller reboots the Web server subsystem automatically. Do not power-cycle during this window (typically 20–30 seconds).

8.4 Reset default credentials

After a reset, the default credentials are:

Change the default password before placing the controller into a production network. Use the Web UI: User administration → admin → Change password. Confirm the change with a logout/login cycle.

9. Activating Communication Services via SCOUT TIA

Reference: SIMOTION IT Diagnostics and Configuration Diagnostics Manual — section 3.3 "Activating communications services in SCOUT TIA".

To activate the Web server and associated services on the controller:

1. In the SCOUT TIA project tree, select the D455-2 device.
2. Open Properties → Web server.
3. Check Activate Web server. Choose HTTP (port 80), HTTPS (port 443), or both. If both are selected, set the redirect behavior: HTTP → HTTPS redirect (301) is recommended for production.
4. Open Properties → Communication services.
5. Enable FTP and Telnet only if you actively need them. Current Siemens security guidance is to leave both disabled in production and use the Web server diagnostics over HTTPS.
6. Download the configuration to the controller.

10. Verification and Acceptance Test

Run the following tests in order. Stop at the first failure and re-open the corresponding section.

1. Web server login page loads: Browse to https://<controller-ip>/. The SIMOTION IT login page must appear within 3 seconds. If you see "connection refused", re-do step 8.3 and confirm the download completed.
2. Login with admin/admin succeeds: If you did not yet change the default password, log in with admin / admin. Failure here means the user DB was recreated but not downloaded correctly.
3. Diagnostic page renders: Click Diagnostics in the Web UI. A populated page confirms the daemon is reading runtime data correctly. Look for the controller name, firmware version, and active alarm count.
4. FTP/Telnet behave as configured: If FTP/Telnet are still disabled, both ports should return "connection refused" — this is expected. If they are enabled, log in with the credentials set in step 8.3.
5. SCOUT TIA online: Confirm the engineering tool can still go online. This validates that the user database reset did not disturb the S7-comm channel.
6. Controller cycles normally: Run the machine for at least one full motion cycle to confirm the Web server reset did not interrupt the runtime.
7. Diagnostic buffer is clean: Re-read the controller diagnostic buffer and confirm no new WEB or USER entries were logged during the verification cycle.

Optional CLI verification from the engineering station:

curl -v -k https://<controller-ip>/ --max-time 5
ping -n 5 <controller-ip>
nslookup <controller-ip>  (if DNS is in use)

11. Preventing Recurrence

The single largest source of UserDataBase.xml corruption is uncontrolled power-down during download. Apply these controls in order of impact.

• UPS on the controller section: A 5-minute UPS that covers the controller, CF card, and PROFINET switch prevents corruption from mains dips and E-stops. Recommended minimum: 24 V DC UPS or AC UPS sized for the panel.
• Read-only CF card mode: The D4x5-2 supports a write-protected mode for the user database. Activate this after each commissioning milestone via SCOUT TIA → Web server → Lock user database.
• Scheduled export of the user database: After any user administration change, export UserDataBase.xml from the controller (SCOUT TIA → Web server → Export) and store it in the project archive.
• Change management: Treat firmware updates as a controlled operation. Always go through the full upload → project compare → download → verification cycle. Skipping the upload step is the most common route to user DB mismatch.
• Avoid manual XML edits: Always edit the user database through SCOUT TIA, not by opening UserDataBase.xml in a text editor. Manual edits frequently introduce BOM (byte order mark) or encoding mismatches.
• CF card replacement schedule: Industrial CompactFlash cards have a finite write endurance (typically 100,000–1,000,000 write cycles per sector). Replace cards every 5 years in production or sooner in high-write environments.

12. Diagnostic Matrix — Adjacent Symptoms

Use this matrix to confirm you are on the correct repair path. Each row maps a symptom pattern to the most likely cause and the relevant section of this article.

13. Commissioning and Reference Documents

The official commissioning document for the D4x5-2 family — including detailed Web server configuration — is available from Siemens Industry Online Support:

• SIMOTION D4x5-2 Commissioning Manual (PDF, entry 109963303)
• SIMOTION IT Diagnostics and Configuration Diagnostics Manual (entry 109963298)

Refer to the Commissioning Manual for the full pin-out of the D455-2 redesign, the CompactFlash card layout, and the boot sequence that determines when each service becomes reachable. The SIMOTION IT manual covers the security concept in detail and lists every configurable parameter for HTTP/S, FTP, and Telnet.

For additional support beyond self-repair, escalate through the official Siemens Industry Online Support portal with the diagnostic buffer entries, the curl output from step 7.7, and the firmware/SCOUT version matrix from section 2. Siemens technical support can match the symptom against known firmware advisories and provide patch firmware if a known bug is identified.

Frequently Asked Questions