diff -r 3c75707045f5 Doc/library/socket.rst
--- a/Doc/library/socket.rst	Wed May 11 11:53:01 2016 +1000
+++ b/Doc/library/socket.rst	Thu May 19 18:51:46 2016 -0700
@@ -326,12 +326,17 @@
    .. versionadded:: 3.3
 
 
-.. data:: SIO_*
+.. data:: SIO_RCVALL
+          SIO_KEEPALIVE_VALS
+          SIO_LOOPBACK_FAST_PATH
           RCVALL_*
 
    Constants for Windows' WSAIoctl(). The constants are used as arguments to the
    :meth:`~socket.socket.ioctl` method of socket objects.
 
+   .. versionchanged:: 3.6
+      ``SIO_LOOPBACK_FAST_PATH`` was added.
+
 
 .. data:: TIPC_*
 
@@ -994,6 +999,12 @@
    On other platforms, the generic :func:`fcntl.fcntl` and :func:`fcntl.ioctl`
    functions may be used; they accept a socket object as their first argument.
 
+   Currently only the following control codes are supported:
+   ``SIO_RCVALL``, ``SIO_KEEPALIVE_VALS``, and ``SIO_LOOPBACK_FAST_PATH``.
+
+   .. versionchanged:: 3.6
+      ``SIO_LOOPBACK_FAST_PATH`` was added.
+
 .. method:: socket.listen([backlog])
 
    Enable a server to accept connections.  If *backlog* is specified, it must
diff -r 3c75707045f5 Doc/whatsnew/3.6.rst
--- a/Doc/whatsnew/3.6.rst	Wed May 11 11:53:01 2016 +1000
+++ b/Doc/whatsnew/3.6.rst	Thu May 19 18:51:46 2016 -0700
@@ -259,6 +259,14 @@
 (Contributed by Wolfgang Langner in :issue:`26587`).
 
 
+socket
+------
+
+The :func:`~socket.socket.ioctl` function now supports the :data:`~socket.SIO_LOOPBACK_FAST_PATH`
+control code.
+(Contributed by Daniel Stokes in :issue:`26536`.)
+
+
 socketserver
 ------------
 
diff -r 3c75707045f5 Lib/test/test_socket.py
--- a/Lib/test/test_socket.py	Wed May 11 11:53:01 2016 +1000
+++ b/Lib/test/test_socket.py	Thu May 19 18:51:46 2016 -0700
@@ -1217,6 +1217,16 @@
         self.assertRaises(ValueError, s.ioctl, -1, None)
         s.ioctl(socket.SIO_KEEPALIVE_VALS, (1, 100, 100))
 
+    @unittest.skipUnless(os.name == "nt", "Windows specific")
+    @unittest.skipUnless(hasattr(socket, 'SIO_LOOPBACK_FAST_PATH'),
+                         'Loopback fast path support required for this test')
+    def test_sio_loopback_fast_path(self):
+        s = socket.socket()
+        self.addCleanup(s.close)
+        s.ioctl(socket.SIO_LOOPBACK_FAST_PATH, True)
+        self.assertRaises(TypeError, s.ioctl, socket.SIO_LOOPBACK_FAST_PATH, None)
+
+
     def testGetaddrinfo(self):
         try:
             socket.getaddrinfo('localhost', 80)
diff -r 3c75707045f5 Misc/ACKS
--- a/Misc/ACKS	Wed May 11 11:53:01 2016 +1000
+++ b/Misc/ACKS	Thu May 19 18:51:46 2016 -0700
@@ -1415,6 +1415,7 @@
 Richard Stoakley
 Peter Stoehr
 Casper Stoel
+Daniel Stokes
 Michael Stone
 Serhiy Storchaka
 Ken Stox
diff -r 3c75707045f5 Modules/socketmodule.c
--- a/Modules/socketmodule.c	Wed May 11 11:53:01 2016 +1000
+++ b/Modules/socketmodule.c	Thu May 19 18:51:46 2016 -0700
@@ -4049,6 +4049,17 @@
             return set_error();
         }
         return PyLong_FromUnsignedLong(recv); }
+#if defined(SIO_LOOPBACK_FAST_PATH)
+    case SIO_LOOPBACK_FAST_PATH: {
+        unsigned int option;
+        if (!PyArg_ParseTuple(arg, "kI:ioctl", &cmd, &option))
+            return NULL;
+        if (WSAIoctl(s->sock_fd, cmd, &option, sizeof(option),
+                         NULL, 0, &recv, NULL, NULL) == SOCKET_ERROR) {
+            return set_error();
+        }
+        return PyLong_FromUnsignedLong(recv); }
+#endif
     default:
         PyErr_Format(PyExc_ValueError, "invalid ioctl command %d", cmd);
         return NULL;
@@ -4059,7 +4070,8 @@
 \n\
 Control the socket with WSAIoctl syscall. Currently supported 'cmd' values are\n\
 SIO_RCVALL:  'option' must be one of the socket.RCVALL_* constants.\n\
-SIO_KEEPALIVE_VALS:  'option' is a tuple of (onoff, timeout, interval).");
+SIO_KEEPALIVE_VALS:  'option' is a tuple of (onoff, timeout, interval).\n\
+SIO_LOOPBACK_FAST_PATH: 'option' is a boolean value, and is disabled by default");
 #endif
 
 #if defined(MS_WINDOWS)
@@ -7268,8 +7280,16 @@
 
 #ifdef SIO_RCVALL
     {
-        DWORD codes[] = {SIO_RCVALL, SIO_KEEPALIVE_VALS};
-        const char *names[] = {"SIO_RCVALL", "SIO_KEEPALIVE_VALS"};
+        DWORD codes[] = {SIO_RCVALL, SIO_KEEPALIVE_VALS,
+#if defined(SIO_LOOPBACK_FAST_PATH)
+			SIO_LOOPBACK_FAST_PATH
+#endif
+		};
+        const char *names[] = {"SIO_RCVALL", "SIO_KEEPALIVE_VALS",
+#if defined(SIO_LOOPBACK_FAST_PATH)
+			"SIO_LOOPBACK_FAST_PATH"
+#endif
+		};
         int i;
         for(i = 0; i<Py_ARRAY_LENGTH(codes); ++i) {
             PyObject *tmp;