What is a Web Server?
A web server is a system that makes web pages or web applications available via HTTP or HTTPS. In OT environments, a web server is often used to view or modify device settings through a standard web browser.
Web servers are present in many industrial components such as PLCs, HMIs, Drives, Switches, Sensors and Firewalls for local configuration and diagnostics.
🧠 How does a web server work?
-
A client (such as a laptop or Engineering Station) sends a request to a device via the HTTP(S) protocol (e.g.
http://192.168.0.10). - The web server on the device handles the request and returns an HTML page.
- Through the browser, the user can:
- View status information
- Modify configuration parameters
- View log files
- Carry out firmware updates
- Many web servers use simple built-in interfaces, sometimes with JavaScript, iframes or even Java applets.
🏭 Application of web servers in industrial networks
- Web interface of a PLC or HMI for status diagnostics and IP configuration
- Configuring a variable frequency drive via the built-in web page
- Configuration of an Industrial Ethernet Switch (such as Hirschmann, Moxa, Cisco IE)
- Firewall management via a web interface on OT devices
- Firmware updates or backups of settings via web-based tools
Web servers enable quick access to device settings, often without additional software.
🔍 Web server vs. engineering software
| Aspect | Web server | Engineering software |
|---|---|---|
| Access | Via browser, platform-independent | Requires installation of specific software |
| Ease of use | Simple, intuitive | More complex, but more powerful |
| Functional scope | Basics: configuration, monitoring | Full: programming, logging, debugging |
| Application | Management and maintenance | Development and in-depth analysis |
| Security | Depends on authentication + HTTPS | Often better isolated within the engineering network |
🔐 Security aspects
- Web servers are often the first attack vector in industrial networks
- Always use HTTPS instead of HTTP (where supported)
- Change default passwords and accounts immediately
- Restrict access to web interfaces via Firewall, ACL or VLAN
- Monitor login attempts via SIEM or Syslog
- Disable unused web servers or features when not needed
Web interfaces are convenient, but they pose a major risk if left unprotected.
📌 In summary
A web server provides simple, fast access to the configuration and status of industrial devices via a browser. User-friendly, but potentially vulnerable – security is therefore crucial.