samba-tool tries to use IPv6 for Secondary DC, even if host doesn't have it, but Primary DC have IPv6 (Dual-Stacked).

Guys,

I'm facing this problem too:
https://lists.samba.org/archive/samba/2013-March/172230.html

NOTE: I just posted this message on Samba maillist but, this seems to be a BUG, so, I'm opening it here too.

---
The problem is:

* samba-tool must use IPv6 ONLY IF the machine have IPv6.
* samba-tool must be able to join a IPv4-Only Secondary DC, into a Dual-Stacked "Samba4 AC DC".
---

I have two Samba4 AC DC, in both located in my office, dual-stacked, working like a charm.

Now, I need to deploy a third DC, located within Amazon EC2, which does NOT have IPv6.

But, samba-tool fails to join.

How can I workaround this, without enabling a tunneled IPv6 within my EC2 ?

Exemplifying:

1- ubuntu-ad-1 - Master - ok - office LAN1 - IPv4 / IPv6
2- ubuntu-ad-2 - Slave - ok - office LAN2 - IPv4 / IPv6

3- ubuntu-ad-3 - Slave can't join - AWS - IPv4-Only

---
root@ubuntu-ad-3:~# kinit administrator
Password for <email address hidden>:
Warning: Your password will expire in 40 days on Thu 28 Aug 2014 05:56:10 PM UTC
---

---
root@ubuntu-ad-3:~# samba-tool domain join central.domain.com.br DC -Uadministrator --realm=CENTRAL.DOMAIN.COM.BR --dns-backend=BIND9_DLZ
Finding a writeable DC for domain 'central.domain.com.br'
ERROR(exception): uncaught exception - Failed to find a writeable DC for domain 'central.domain.com.br'
  File "/usr/lib/python2.7/dist-packages/samba/netcmd/__init__.py", line 175, in _run
    return self.run(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/samba/netcmd/domain.py", line 552, in run
    machinepass=machinepass, use_ntvfs=use_ntvfs, dns_backend=dns_backend)
  File "/usr/lib/python2.7/dist-packages/samba/join.py", line 1150, in join_DC
    machinepass, use_ntvfs, dns_backend, promote_existing)
  File "/usr/lib/python2.7/dist-packages/samba/join.py", line 76, in __init__
    ctx.server = ctx.find_dc(domain)
  File "/usr/lib/python2.7/dist-packages/samba/join.py", line 262, in find_dc
    raise Exception("Failed to find a writeable DC for domain '%s'" % domain)
---

Debugging it with `strace`, I'm seeing:

---
strace -f -e trace=network samba-tool domain join CENTRAL.DOMAIN.COM.BR DC -Uadministrator --realm=CENTRAL.DOMAIN.COM.BR --dns-backend=BIND9_DLZ
.....
[pid 1533] +++ killed by SIGKILL +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_KILLED, si_pid=1533, si_status=SIGKILL, si_utime=0, si_stime=0} ---
socket(PF_INET6, SOCK_DGRAM, IPPROTO_IP) = 5
setsockopt(5, SOL_IPV6, IPV6_V6ONLY, [1], 4) = 0
connect(5, {sa_family=AF_INET6, sin6_port=htons(389), inet_pton(AF_INET6, "2001:1291:XXX:85Xa::66XX", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, 28) = -1 ENETUNREACH (Network is unreachable)
ERROR(exception): uncaught exception - Failed to find a writeable DC for domain 'CENTRAL.DOMAIN.COM.BR'
  File "/usr/lib/python2.7/dist-packages/samba/netcmd/__init__.py", line 175, in _run
    return self.run(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/samba/netcmd/domain.py", line 552, in run
    machinepass=machinepass, use_ntvfs=use_ntvfs, dns_backend=dns_backend)
  File "/usr/lib/python2.7/dist-packages/samba/join.py", line 1150, in join_DC
    machinepass, use_ntvfs, dns_backend, promote_existing)
  File "/usr/lib/python2.7/dist-packages/samba/join.py", line 76, in __init__
    ctx.server = ctx.find_dc(domain)
  File "/usr/lib/python2.7/dist-packages/samba/join.py", line 262, in find_dc
    raise Exception("Failed to find a writeable DC for domain '%s'" % domain)
+++ exited with 255 +++
---

So, how can I force samba-tool to use IPv4? Since ubuntu-ad-3 doesn't have IPv6...

Thanks!
Thiago