I have a very odd issue with two of our domain controller in the same site (Physical and AD).
Both stop being able to resolve to a specific external website address.
This doesn't affect anything else bar this address, e.g. when you get the issue that the DC can't get to anything with a suffix *.fr.
If i clear the DNS cache you will then be able to resolve to the offending address, however in ten miniutes or so you will be unable to resolve to the address again, unless you reboot the DC or clear the cache again.
This doesn't affect any other DCs in the domain worldwide, they always resolve to the same IP. We have checked with the ISP and they say they have no issue resolving.
What makes it even odder is that this only affects the www address. if we do a nslookup on the domain name that will resolve with no issues.