diff -r 554e18a639a5 Lib/ipaddress.py
--- a/Lib/ipaddress.py	Sat Oct 17 16:25:07 2015 +0300
+++ b/Lib/ipaddress.py	Sat Oct 17 16:37:13 2015 +0300
@@ -673,8 +673,10 @@
             return False
         # dealing with another network.
         if isinstance(other, _BaseNetwork):
-            return False
-        # dealing with another address
+            if self._prefixlen <= other._prefixlen:
+                return other.network_address._ip & self.netmask._ip == self.network_address._ip
+            else:
+                return False
         else:
             # address
             return other._ip & self.netmask._ip == self.network_address._ip
diff -r 554e18a639a5 Lib/test/test_ipaddress.py
--- a/Lib/test/test_ipaddress.py	Sat Oct 17 16:25:07 2015 +0300
+++ b/Lib/test/test_ipaddress.py	Sat Oct 17 16:37:13 2015 +0300
@@ -612,10 +613,18 @@
             self.assertIn(obj, self.v4net)
         for obj in self.v6_addresses:
             self.assertIn(obj, self.v6net)
-        for obj in self.v4_objects + [self.v6net]:
+        for obj in self.v4_objects:
             self.assertNotIn(obj, self.v6net)
-        for obj in self.v6_objects + [self.v4net]:
+        for obj in self.v6_objects:
             self.assertNotIn(obj, self.v4net)
+        self.assertIn(self.v6net, self.v6net)
+        self.assertNotIn(ipaddress.IPv6Network("::2/127"),
+                         ipaddress.IPv6Network("::4/127"))
+        # ip == other ip. should be compared by prefix len
+        self.assertNotIn(ipaddress.IPv6Network("1::/56"),
+                         ipaddress.IPv6Network("1::/64"))
+        self.assertIn(ipaddress.IPv6Network("1::/64"),
+                      ipaddress.IPv6Network("1::/56"))
 
     def test_mixed_type_ordering(self):
         for lhs in self.objects: