>>>Some days ago I installed my ASP.NET application on a customer's web server. Everything went well. But when I was setting a web site I had to choose a port number (default was 80 and it was no go). So I assigned port 900 for one application and 901 for another (I installed two web sites and two applications). It worked. But I simply guessed the numbers 900 and 901. What are the right way of assigning port numbers for an intranet (note, not Internet) sites?
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>>>Thank you in advance for any suggestions.
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I'm not quite sure why you're mapping ports? Is there something special you're trying to accomplish? You can run multiple web apps. on the same port using IIS and host header mapping. If you don't have a "real" dns name (eg. you're using an IP address), you can install each app into it's own virtual directory. The url then becomes something like http://ipaddress/virtualdir/default.aspx

The other thing you can do (if, for example, you have an intranet site and a public website for the same domain name) is to just change the host portion of the name, eg. www.mycompany.com is the public site and intranet.mycompany.com is the internal site.