>>>>>>>>>Hi,
>>>>>>>>>
>>>>>>>>>I am trying to install a web application on the customer web server. The customer asked that I set up port 443 for this Site. But when I do and try to start the site I get the message that "Another Web Site maybe using this port". I can set up any other port # but the 443. How do I find out what site is using this port 443 (I checked all sites in the IIS and none is using this port, as far as I can see).
>>>>>>>>
>>>>>>>>443 is the default port for HTTPS. You'll need to check for existing sites that support HTTPS.
>>>>>>>>
>>>>>>>>http://www.howtogeek.com/howto/28609/how-can-i-tell-what-is-listening-on-a-tcpip-port-in-windows/
>>>>>>>
>>>>>>>Thank you. This explain the problem. My app is using HTTP and not HTTPS. So I need to learn how to use HTTPS instead of HTTP.
>>>>>>
>>>>>>Hmm. If another site is using 443 then switching to https isn't going to help - you still have a conflict.
>>>>>
>>>>>I think that the problem is that 443 can only be used with https and with certificate.
>>>>
>>>>Not true. As Al mentioned 443 is the default port for HTTPS. But all that means is that if you enter 'https:xxx.com' in the browser it will try hitting the server on 443 (in just the same way if you entered http:xxx.com it would default to port 80). There's nothing that says that a server has to listen on 80 or 443 - any ports can be used for either http or https.
>>>>
>>>
>>>You are probably right. The reason I said it that when I contacted the custom IT and said that something is blocking your port 443, he asked me "what cert are you using." then he added "this needs to be SSL not just port 443". So I presumed that I need to get some kind of certificate. How do you get them? Is this certificate makes the site "SSL"?
>>
>>SSL needs a certificate. It can be self-signed but for a public site you should purchase one from a known certification authority (e.g. VeriSign) so that users browsers will automatically accept the certificate. The certificate needs to match the site url....
>
>Thank you. Do you think it is a valid question to a customer if they already have a number of certificates? Or usually the customer or vendor buys one when they set up a site?

You might want to take a step back and focus on what you're trying to do.

At the beginning you said "I am trying to install a web application on the customer web server". Well and good. When the customer asked you to set it up on port 443, you can't do that because some other web site or service is already using that port.

Now you need to go back to the customer and report that some other process is already listening on port 443 (you can tell what it is from the link I sent earlier). Can the customer clarify that they actually want port 443, or is it that their way of saying they want a secure site using https: / SSL? If it's an intranet app maybe they'd be OK with plain http: which would save you some hassle.

If port 443 is being legitimately used for some other https: / SSL site, and port 80 for some other http: site then you'll have to use some other port(s) for your web app, and users will have to access it by specifying the port in the URL.