As is with the rest of the tools, this one was also born out of necessity and I decided to share it with everyone. But some people are not comfortable putting my scripts on their site. That's cool and I don’t blame them, they don’t know me. So here I am going to explain how to display or print the user's IP address and host name using a number of server-side technologies.
A common issue with the above calls is that in many cases host names may be returned as IP addresses or nothing at all. In some cases that is because no reverse record for a client's IP address is available. But if this issues occurs all the time, it could mean that reverse resolution is turned off. This is generally done for performance reason, to save on server resources.
You can ask your hosting company to turn that service on, or you could configure reverse lookup yourself if you have access to the server configuration files. Here’s how reverse look up is switched on for Internet Information Server (IIS) and Apache.
By the way, if you ever wanted to run a simple reverse lookup on an IP address, here's a Reverse Whois tool for that job.
Before I end this post, here's one more piece of information for those who might wonder where parameters like REMOTE_ADDR or REMOTE_HOST come from. Those are part of a collection of parameters known as environment variables that web servers are expected to make available to the scripts. Want the gory details? Read here.