Siemens ADSL 500 - Manual (Page 37)

Chapter 4 Configuration
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8. Enable Specify an IP address option. Enter the IP Address: 192.168.1.x (x is between 2 and 254) and Subnet
Mask: 255.255.255.0 and Default Gateway: 192.168.1.1 as in figure below.
9. When returning to Network window, click Close.
10. When prompted with Network Settings Change dialog box, click Yes to restart your computer.