[Samba] “Failed to find a writeable DC for domain” joining to win2k3 AD DC

[Kevin Field]

I have a CentOS 6.4 box with SerNet's Samba 4.0.8 installed and no 
smb.conf file yet, as it should be. I want it to become an AD DC in my 
existing Windows domain, replicating from the existing Windows Server 
2003 box. I have SELinux enabled and want it to stay that way.

I'm getting this error trying to run samba-tool:

$ sudo samba-tool domain join currentwindowsadserver.mydomain.lan DC 
-Uadministrator --realm=currentwindowsadserver.mydomain.lan
Finding a writeable DC for domain 'currentwindowsadserver.mydomain.lan'
ERROR(exception): uncaught exception - Failed to find a writeable DC for 
domain 'currentwindowsadserver.mydomain.lan'
   File "/usr/lib64/python2.6/site-packages/samba/netcmd/__init__.py", 
line 175, in _run
     return self.run(*args, **kwargs)
   File "/usr/lib64/python2.6/site-packages/samba/netcmd/domain.py", 
line 552, in run
     machinepass=machinepass, use_ntvfs=use_ntvfs, dns_backend=dns_backend)
   File "/usr/lib64/python2.6/site-packages/samba/join.py", line 1082, 
in join_DC
     machinepass, use_ntvfs, dns_backend, promote_existing)
   File "/usr/lib64/python2.6/site-packages/samba/join.py", line 73, in 
__init__
     ctx.server = ctx.find_dc(domain)
   File "/usr/lib64/python2.6/site-packages/samba/join.py", line 246, in 
find_dc
     raise Exception("Failed to find a writeable DC for domain '%s'" % 
domain)

I have a StackExchange thread open with all the things I've tried 
changing and all the things I've verified so far:

http://unix.stackexchange.com/questions/86516/samba-4-gives-failed-to-find-a-writeable-dc-for-domain-on-samba-tool-domain-jo

I'd appreciate any pointers.  I seem to have run out of things to try.

Thanks,
Kev