diff --git a/pydu/network.py b/pydu/network.py
index b9efb56..0b100ca 100644
--- a/pydu/network.py
+++ b/pydu/network.py
@@ -1,5 +1,6 @@
 import socket
 import struct
+from pydu.platform import POSIX
 
 
 # https://github.com/kennethreitz/requests/blob/master/requests/utils.py
@@ -13,31 +14,30 @@ def dotted_netmask(mask):
     return socket.inet_ntoa(struct.pack('>I', bits))
 
 
+# https://github.com/kennethreitz/requests/blob/master/requests/utils.py
 def is_ipv4(ip):
     """
     Returns True if the IPv4 address ia valid, otherwise returns False.
     """
-    return _is_ip(ip, af=socket.AF_INET)
-
-
-def is_ipv6(ip):
-    """
-    Returns True if the IPv6 address ia valid, otherwise returns False.
-    """
-    return _is_ip(ip, af=socket.AF_INET6)
-
-
-def _is_ip(ip, af):
-    '''
-    Returns True if the IP address ia valid, otherwise returns False.
-    '''
     try:
-        socket.inet_pton(af, ip)
+        socket.inet_aton(ip)
     except socket.error:
         return False
     return True
 
 
+if POSIX:
+    def is_ipv6(ip):
+        """
+        Returns True if the IPv6 address ia valid, otherwise returns False.
+        """
+        try:
+            socket.inet_pton(socket.AF_INET6, ip)
+        except socket.error:
+            return False
+        return True
+
+
 def get_free_port():
     s = socket.socket(socket.AF_INET, type=socket.SOCK_STREAM)
     s.bind(('127.0.0.1', 0))
diff --git a/tests/test_network.py b/tests/test_network.py
index 4419f1c..41b6c19 100644
--- a/tests/test_network.py
+++ b/tests/test_network.py
@@ -1,6 +1,8 @@
 import pytest
-from pydu.platform import WINDOWS
-from pydu.network import dotted_netmask, is_ipv4, is_ipv6, get_free_port
+from pydu.platform import POSIX
+from pydu.network import dotted_netmask, is_ipv4, get_free_port
+if POSIX:
+    from pydu.network import is_ipv6
 
 
 @pytest.mark.parametrize(
@@ -13,7 +15,6 @@ def test_dotted_netmask(mask, expected):
     assert dotted_netmask(mask) == expected
 
 
-@pytest.mark.skipif(WINDOWS, reason='Not support on windows')
 class TestIsIPv4Address:
 
     def test_valid(self):
@@ -24,7 +25,7 @@ class TestIsIPv4Address:
         assert not is_ipv4(value)
 
 
-@pytest.mark.skipif(WINDOWS, reason='Not support on windows')
+@pytest.mark.skipif(not POSIX, reason='Not support on No-POSIX system')
 class TestIsIPv6Address:
 
     def test_valid(self):