In this article we are going to create a whois lookup client application. The main aim of this application will be to look up information about websites on various known WHOIS servers.
Creating a WHOIS Lookup Client - DNS Resolution (Page 2 of 4 )
As stated earlier, DNS resolution is basically just another way to gather more information about a domain. In this case, we can find out how many IP addresses a particular domain uses and also how many variations there are of this domain. For example, yahoo.com has many different IP addresses and also many different variations based on which country it services:
The other obvious use of a DNS resolver is to map a domain name (that does not necessarily have multiple addresses) to an IP address and vice versa. Again, this just gives you the means to mount an effective search for information about an IP address or domain name. One application of this function is that it can be used in tracing spammers. The Delphi implementation of the DNS resolver provides us with a variety of ways to query for domain information. You can query for the following and more:
Mailbox Domain Name -- Traces the domain name of an email address. Useful for tracing spammers.
Host address.
Mailbox or mail list information.
Domain name pointer.
Although there are other queries that can be executed, I want to focus only on the host address information at this stage.
What will this program do?
Basically the program is going to query any WHOIS database, mainly for domain related information. This is because we do not know what kind of information a particular WHOIS server has in its database. The only thing we can be sure of is that a WHOIS database has to store information about a domain, so we'll go with that option. The application will enable you to add as many WHOIS server addresses to it as you want, which will in turn enable you to get a wide variety of information about a domain. It will also contain an option for you to find the number of IP addresses related to a specific domain.
To create this program you will need Borland Delphi 6 or higher, with Indy 10.1.5 or higher. Keep in mind that if you do not use the exact same Indy version, there may be some subtle differences in terms of functions used in this program, therefore the program might not work. So it is probably best for you to try and install Indy 10.1.5. All of the latest Indy versions are available from http://www.indyproject.org/.
Delphi-Kylix 
Building an IRC Client
