HTRegz is right if you can't connect to the ip address it has nothing to do with DNS. Typeing in the ip will completely bypass DNS.

a few handy tricks to troubbleshooting network/internet problems is:

Ping "hostname/IP"
Here you can see several things. The first you can see is if your DNS resolves the hostname to an ip address or not. Also if ICMP is allowed you can confirm that you can actually reach the ip/hostname in question.
If it fails to resolve the hostname, you have either made a typo or you have a DNS related problem.

If your DNS resolves the hostname as it should but you can't reach the IP address. Try a telnet "hostname/ip" "port". As an example if your trying to access your webserver the following line will show you if you have connectivity.

telnet www.domain.com 80
once connected the type the following line to query the server
gethtml

You will probably not be able see more than the webserver giving you a bad request - but from this we at least learned that it is responsive on the following port. If you are denied - you reach the server but the service isn't available. If you get a timeout it might be once again a typo or you can't actually reach the ip in question.


If you are sure the service is running, check if ICMP is allowed or not.

Then traceroute (tracert in windows if i remember correctly) "hostname/IP"

This will show the route you take across the internet. If you get a timeout on the way, the two most commen reasons are,

1) ICMP is not allowed
2) Routing problem

The easiest (not bulletproof though) way to determine if it a routing problem is to look at the hops. If it dies nowhere near the ip address you're trying to reach it might very well be buggy routing, if it dies one or two hops before you should reach the ip it is most likely ICMP.

Without more detailed information it could be everything from buggy routing to filtering, a typo in the firewall forward rule etc. So instead of assuming what is the problem i recommend eliminating the possibilities one by one and hopefully you will see the light along the way.

Since u can only see it through a proxy it might be some internal routing bug (an interface on your POP wrongly configured with the ip that now belongs to your company) or alike that gives you problemes.

Remember that if you find any evidence on ping/telnet/traceroute make sure to send it to your ISP. This tends either to help them locate the problem or better yet makes it very hard for them to ignore the error and write it off as "dumb" customer that actually has no problems.