Autodetect IPv6 connectivity from minion to master

doc/ref/configuration/minion.rst

@@ -81,9 +81,10 @@ The option can can also be set to a list of masters, enabling
 ``ipv6``
 --------
 
-Default: ``False``
+Default: ``None``
 
-Whether the master should be connected over IPv6.
+Whether the master should be connected over IPv6. By default salt minion
+will try to automatically detect IPv6 connectivity to master.
 
 .. code-block:: yaml
 

salt/config/__init__.py

@@ -990,7 +990,7 @@ DEFAULT_MINION_OPTS = {
     'mine_interval': 60,
     'ipc_mode': _DFLT_IPC_MODE,
     'ipc_write_buffer': _DFLT_IPC_WBUFFER,
-    'ipv6': False,
+    'ipv6': None,
     'file_buffer_size': 262144,
     'tcp_pub_port': 4510,
     'tcp_pull_port': 4511,

salt/transport/zeromq.py

@@ -346,7 +346,7 @@ class AsyncZeroMQPubChannel(salt.transport.mixins.auth.AESPubClientMixin, salt.t
                 zmq.RECONNECT_IVL_MAX, self.opts['recon_max']
             )
 
-        if self.opts['ipv6'] is True and hasattr(zmq, 'IPV4ONLY'):
+        if (self.opts['ipv6'] is True or ':' in self.opts['master_ip']) and hasattr(zmq, 'IPV4ONLY'):
             # IPv6 sockets work for both IPv6 and IPv4 addresses
             self._socket.setsockopt(zmq.IPV4ONLY, 0)
 

salt/utils/__init__.py

@@ -716,12 +716,25 @@ def ip_bracket(addr):
     return addr
 
 
-def dns_check(addr, safe=False, ipv6=False):
+def dns_check(addr, safe=False, ipv6=None):
     '''
     Return the ip resolved by dns, but do not exit on failure, only raise an
     exception. Obeys system preference for IPv4/6 address resolution.
     '''
     error = False
+
+    # Detect IPv6 support if it is not forced by trying to connect
+    # to the give address over IPv6.
+    if ipv6 is None:
+        s = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
+        try:
+            s.connect((addr, 0))
+            s.close()
+
+            ipv6 = True
+        except:
+            ipv6 = False
+
     try:
         # issue #21397: force glibc to re-read resolv.conf
         if HAS_RESINIT: