Re: not DNS, but routing issues
Such a routing failure amkes large amounts of the Internet inaccessible. traffic simply can't get there. Due to the fact that routers attempt to automatically correct around failures, this can mean that some sites are periodically accessible or accessible by one user and not another.
In this case, the DNS servers you were using were one of the parts of the network you couldn't reach (or the PN DNS servers couldn't reach other upstream DNS servers) so it looks to you like it's a DNS problem when the real problem actually lies elsewhere.
In your case, the sites you wre trying to access were in the subset of the network you could actually reach. Lucky you :) - You would have found other sites that were inaccessible.
All the handwaving claiming that chaing DNS servers fixes the issue just muddies the waters.
Biting the hand that feeds IT
