diff --git a/telethon/telegram_bare_client.py b/telethon/telegram_bare_client.py
index a9e2fb30..cd01f009 100644
--- a/telethon/telegram_bare_client.py
+++ b/telethon/telegram_bare_client.py
@@ -39,6 +39,11 @@ from .update_state import UpdateState
 from .utils import get_appropriated_part_size
 
 
+DEFAULT_IPV4_IP = '149.154.167.51'
+DEFAULT_IPV6_IP = '[2001:67c:4e8:f002::a]'
+DEFAULT_PORT = 443
+
+
 class TelegramBareClient:
     """Bare Telegram Client with just the minimum -
 
@@ -69,6 +74,7 @@ class TelegramBareClient:
 
     def __init__(self, session, api_id, api_hash,
                  connection_mode=ConnectionMode.TCP_FULL,
+                 use_ipv6=False,
                  proxy=None,
                  update_workers=None,
                  spawn_read_thread=False,
@@ -80,6 +86,8 @@ class TelegramBareClient:
                 "Your API ID or Hash cannot be empty or None. "
                 "Refer to Telethon's README.rst for more information.")
 
+        self._use_ipv6 = use_ipv6
+        
         # Determine what session object we have
         if isinstance(session, str) or session is None:
             session = Session.try_load_or_create_new(session)
@@ -88,6 +96,11 @@ class TelegramBareClient:
                 'The given session must be a str or a Session instance.'
             )
 
+        if not session.server_address:
+            session.port = DEFAULT_PORT
+            session.server_address = \
+                DEFAULT_IPV6_IP if self._use_ipv6 else DEFAULT_IPV4_IP
+
         self.session = session
         self.api_id = int(api_id)
         self.api_hash = api_hash
@@ -282,7 +295,7 @@ class TelegramBareClient:
         return self._recv_thread is not None and \
                threading.get_ident() == self._recv_thread.ident
 
-    def _get_dc(self, dc_id, ipv6=False, cdn=False):
+    def _get_dc(self, dc_id, cdn=False):
         """Gets the Data Center (DC) associated to 'dc_id'"""
         if not TelegramBareClient._config:
             TelegramBareClient._config = self(GetConfigRequest())
@@ -295,7 +308,7 @@ class TelegramBareClient:
 
             return next(
                 dc for dc in TelegramBareClient._config.dc_options
-                if dc.id == dc_id and bool(dc.ipv6) == ipv6 and bool(dc.cdn) == cdn
+                if dc.id == dc_id and bool(dc.ipv6) == self._use_ipv6 and bool(dc.cdn) == cdn
             )
         except StopIteration:
             if not cdn:
@@ -303,7 +316,7 @@ class TelegramBareClient:
 
             # New configuration, perhaps a new CDN was added?
             TelegramBareClient._config = self(GetConfigRequest())
-            return self._get_dc(dc_id, ipv6=ipv6, cdn=cdn)
+            return self._get_dc(dc_id, cdn=cdn)
 
     def _get_exported_client(self, dc_id):
         """Creates and connects a new TelegramBareClient for the desired DC.
diff --git a/telethon/telegram_client.py b/telethon/telegram_client.py
index a5ce4572..ae864ea6 100644
--- a/telethon/telegram_client.py
+++ b/telethon/telegram_client.py
@@ -69,6 +69,7 @@ class TelegramClient(TelegramBareClient):
 
     def __init__(self, session, api_id, api_hash,
                  connection_mode=ConnectionMode.TCP_FULL,
+                 use_ipv6=False,
                  proxy=None,
                  update_workers=None,
                  timeout=timedelta(seconds=5),
@@ -113,6 +114,7 @@ class TelegramClient(TelegramBareClient):
         super().__init__(
             session, api_id, api_hash,
             connection_mode=connection_mode,
+            use_ipv6=use_ipv6,
             proxy=proxy,
             update_workers=update_workers,
             spawn_read_thread=spawn_read_thread,
diff --git a/telethon/tl/session.py b/telethon/tl/session.py
index f597048f..bbdcc590 100644
--- a/telethon/tl/session.py
+++ b/telethon/tl/session.py
@@ -64,8 +64,8 @@ class Session:
         self._last_msg_id = 0  # Long
 
         # These values will be saved
-        self.server_address = '91.108.56.165'
-        self.port = 443
+        self.server_address = None
+        self.port = None
         self.auth_key = None
         self.layer = 0
         self.salt = 0  # Unsigned long