The URL certainly doesn't work now. I tried http://tools.whois.net/whoisbyip
, and I'm redirected to https://tools.whois.net/default.aspx
, where I can only search for a domain name, not an IP address. So whatever service they had that allowed you to do this no longer works.
I searched for the URL you posted and found http://whois.domaintools.com/
, which appears to be the new URL and lets you search by IP, and from there you can get the appropriate URL to do what you want. So your code would then look like this:
<a href="http://whois.domaintools.com/<?php echo $row['ip'];?>" target = "_blank">ISP Details</a></td>
However, in addition to changing the URL, they've also added a CAPTCHA, so the method you're using will no longer work.
UPDATED
The one you posted in your comment would work like this:
https://www.ultratools.com/tools/ipWhoisLookupResult?ipAddress=X.X.X.X
So integrated into your code, it would look like this:
<a href="https://www.ultratools.com/tools/ipWhoisLookupResult?ipAddress=<?php echo $row['ip'];?>" target = "_blank">ISP Details</a></td>