Strange DNS Resolution Issues

[Revital Gorsht]

Hi all,

A few weeks ago, two of several internal DNS servers were suddenly unable 
to resolve some external sites (eg microsoft.com, yahoo.com), while all 
internal and other external sites (eg google.com) were resolving fine. 
Since we couldn't pinpoint the cause, the problem went on for about 5 
hours and then magically fixed itself... we were all left scratching our 
heads.

Yesterday, (two weeks after the initial problem and curiously at around 
the same time) the problem reappeared for about 30 minutes. 

All of our servers (affected and non-affected) are running BIND 9.5.1-P1. 
The failed queries return timeouts or SERVFAILs.  Restarting BIND did not 
fix the problem.  Nothing suspicious in the logs. 

Has anyone else experienced this sort of thing recently? Can anyone point 
me in the right direction?? Is this even a BIND issue???  I'll be more 
than happy to provide any further details!

R.
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