Hi,
Here is my steps to make this happen:
Now, when my users type http://panel.userdomain.com they get redirected to DNP login page.
System Requirements:
DNS Service
One Dedicated IP (in this tutorial I use this example IP: 10.10.10.1)
Custom Login Creation For Users - Step by Step:
1. You should first add 10.10.10.1 to your Primary DNS server as an "A" record with name "Panel".
2. Start installing your DNP version but this time, you should set DNP Portal IP to 10.10.10.1 with port 80.
3. Now, you have to finish server settings in your DNP Server Configuration and just do this trick additionally:
when you configuring "Web" service of your server, scroll down and in DNS section, add an "A" record with name "Panel" pointed to 10.10.10.1
4. Thats it!
Now when you create a new user and add a domain in his/her account, that "A" record will automatically add to domain's DNS records and when you user trying to access http://panel.userdomain.com he/she will get redirect to DNP Portal Login Page ;)
Please Note:
*Please note that 10.10.10.1 was an example IP which I used to write this tutorial and you should put your own dedicated IP which you decided to keep for DNP Portal ONLY!
**If an error appears in step 2, while you set your port to 80, just open IIS and right click on "Default Web Site" and in "IP Adresses" section, choose your other IP address which is available and shared for your webhosting users. (Be sure that its not the IP you decided for DNP Portal otherwise it will not work)
***Any question can be asked either here or by my direct 24/7 available e-mail aria@ariaservers.com
Hope it will be helpful for you all 
AriaServers Networks Ltd.
WebHosting: http://www.ariaservers.com
Domain Registration: http://www.ariaservers.org
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