[Samba] really serious and bizaar problem for us

[Yan Seiner]

Hah!  It must be contagious.  I just went through this.  Check your DNS 
setup.  For some bizarre reason all DNS queries were bouncing off the 
external interface.  When the interface went down, DNS queries failed. 
 Since samba won't allow logons without reverse name resolution, no logons.

So what was the fix?  Check all /etc/resolv.conf (or equivalent), make 
sure they have an entry for 127.0.0.1 and the order hosts, bind, thus:

order hosts,bind
127.0.0.1    localhost localhost.localdomain

In my case, one box had order bind, hosts .  This was enough to bring 
down the entire network. Let me know if this works for you.

HTH,

--Yan