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Entry type: FAQ Entry ID: 33269452, Entry date: 12/29/2008
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Which settings are required to access the web server of the CPU via a PC with a second network card even though a proxy server is set?

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Background:
CPUs with the name extension "PN/DP" have a web server. Here, you can read out data from the CPU via the Ethernet using the web browser.

The information in this entry is based on the following scenario:
You are using a computer with two network cards. The first card is connected with the company intranet and the second with the network in which the CPU is located. The company intranet is connected with the Internet only via a proxy server. A proxy server acts as a broker between the internal network (intranet) and the Internet, which calls the files from the remote web server and makes them available.

If you now enter the CPU's IP address in the browser, the request is sent to the proxy server and not to the CPU. Thus you cannot set up a connection with the CPU.

Solution:
Make one of the two settings to access the CPU despite proxy server:

More information:
More information on this is available in Entry ID: 2073614 "What is the connection between subnet masks and IP addresses in the IP address area, also with regard to subnetting?".
Instructions for using the web server are available in Entry ID: 12996906 section 3.3 Web Server.

Use private IP address
Since the area of the private IP addresses is usually not routed in the Internet, the web browser bypasses the proxy server and queries the private (or local) address directly. Therefore, you use private (or local) addresses for the network in which the CPU is located.

Set a private IP address for the CPU (e.g. 192.168.0.4).


Fig. 01

Set a private IP address for the network card (e.g. 192.168.0.2). The CPU and network card must be in the same network.


Fig. 02

In this example, the CPU is accessible via the web browser at http://192.168.0.4/.

The following ranges are reserved for private networks:

10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255

Exception for proxy server
If you cannot use a private (or local) IP address, you must inform the browser that this address should be accessed directly without proxy.

Enter the CPU's IP address as exception of the proxy server in the PC's web browser. You find the settings in the Internet Explorer under Tools -> Internet Options -> Connections -> LAN Settings -> Proxy Server -> Advanced.

In this example, the CPU is accessible via the (non-private) IP address http://140.0.0.4/. In this example, the IP address is 140.0.0.2 (CPU and network card must be in the same network).

 
Fig. 03

You can also use wildcards, e.g. "140.0.0.*".

In this example, the CPU is accessible via the web browser at http://140.0.0.4/.

Security information
In order to protect technical infrastructures, systems, machines and networks against cyber threats, it is necessary to implement – and continuously maintain – a holistic, state-of-the-art IT security concept. Siemens’ products and solutions constitute one element of such a concept. For more information about cyber security, please visit
https://www.siemens.com/cybersecurity#Ouraspiration.