Don't think I quite understand, or, if I do, why would you want to do such a thing..
Ok, have a form that asks the user if (s)he is a user or a re-seller. Then, create a database that stores this information. Everytime you want to check, you can check to see if the IP address matches the re-sellers/users IP stored within the database. What if the user's IP address changes? What if they access a different computer? Is this therefore a really efficent way to identifying someone?
Here we are talking about Hosting ip address ( You will find on Control panel ). I want to add a reseller using his / her server ip address. Then i will add "A Record" to that ip address using Simple DNS Editor so that the website / sub-domain will map to our domain. Now i want to check the db from that ip address.