Intermitent SERVFAIL

[Arthur Kerpician]

Hi all,
 From time to time, couple of nameservers are returning SERVFAIL when 
querying domains hosted on one of my DNS servers. This behaviour is not 
permanent (sometimes it works sometimes it doesn't) and it's not linked 
to one domain only (but all domains are hosted on my DNS server). The 
nameservers which are giving this error are specially our ISP DNS server 
and even bind servers which I installed.

The server which hosts the domains is using bind9 on FC1. To give you an 
example try dig www.infolitoral.ro and see if it works from your NS and 
then try dig @212.93.136.2 www.infolitoral.ro to get the SERVFAIL. 
However, doing a +trace with the last dig will resolve www.infolitoral.ro.

I really don't know how to debug this problem and localize it on my DNS 
server or my ISP's DNS server.

Thanks for any ideas,
Arthur