Is mustermann.de down or not?

Is it down only for you? Check these instructions

• Use another browser. Check if the pages present the same problem with Internet Explorer, or another browser (Chrome, Firefox, Safari). If the problem also occurs, perform the following actions.
• Use the IP address of website. Every Web site has a unique IP address. If the website you are attempting to visit contains the colon sign followed by a number in your address (for example, http://website.com:23 ), try removing that part ( http://website.com ) or replace it with 80 (http://website.com:80 ). If this does not work, you may not have given a correct address.
• Check DNS cache validity. DNS is the service that converts the website's domain name into an IP address that web browser can use to connect to that site. That information is stored in your device's DNS cache to improve speed. However, if the information stored is corrupt or the website has changed its IP address, the browser may redirect you to another server.
• Maybe website blocked you. Validate that the team administrator does not block these types of pages. In case if not, confirm what type of proxy settings you have to access the pages. To access it in Vista or Windows 7, click Start, type internet options, and press ENTER. In XP, select Start, then Run, type inetcpl.cpl, and press ENTER. Once you're there, click the Security tab, then the Restricted sites icon, followed by the Sites button. If the site's on this list, remove it. Then click the Privacy tab, and, again, the Sites button. Remove the URL if it's there.