We found an ISP unable to route one of our server's dns which keeps dispalying "unknown host" but once they flush the DNS, it works again....It will display "unknown host" again after few days less than a week.
The DNS of the server is running normal which other ISP able to route it..mostly nearly all of the one I know.
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Obviously this is a dns issue, and one that must be resolved with your local ISP, there's nothing anyone here can do about it.
For what it's worth:
Check the domain in question (or hostname) at dnsstuff.com and dnsreport.com. If everything there checks out fine, forward that to your ISP and have them verify that things are working there. If you get any red / yellow areas in dnsreport, check them out before you contact your ISP again.
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