We experimented few DNS issues those last days….Here below the answer of the hoster :
Now, the websites were unavailable for a brief period of time, however the server experienced no loss of functionality. The problem resided in a higher level dns server loosing the zone file for our dns server. You could ping the server by its ip address and it would respond, but if you pinged the server by its hostname it would say ip address not found. That is not a problem with our server in any aspect at all. That is a problem at a higher point in the chain, and apparently it has been corrected as everything works now.