diff --git a/ryu/lib/sockaddr.py b/ryu/lib/sockaddr.py
new file mode 100644
index 00000000..460f2159
--- /dev/null
+++ b/ryu/lib/sockaddr.py
@@ -0,0 +1,74 @@
+# Copyright (C) 2014 Nippon Telegraph and Telephone Corporation.
+# Copyright (C) 2014 YAMAMOTO Takashi <yamamoto at valinux co jp>
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import platform
+import socket
+import struct
+
+from ryu.lib import addrconv
+
+
+system = platform.system()
+if system == 'Linux':
+    # on linux,
+    #    no ss_len
+    #    u16 ss_family
+    _HDR_FMT = "H"
+    _HAVE_SS_LEN = False
+else:
+    # assume
+    #    u8 ss_len
+    #    u8 ss_family
+    _HDR_FMT = "BB"
+    _HAVE_SS_LEN = True
+
+
+# RFC 2553
+_SS_MAXSIZE = 128
+_SS_ALIGNSIZE = 8
+
+_SIN_SIZE = 16  # sizeof(struct sockaddr_in)
+
+_HDR_LEN = struct.calcsize(_HDR_FMT)
+
+
+def _hdr(ss_len, af):
+    if _HAVE_SS_LEN:
+        return struct.pack(_HDR_FMT, ss_len, af)
+    else:
+        return struct.pack(_HDR_FMT, af)
+
+
+def _pad_to(data, total_len):
+    pad_len = total_len - len(data)
+    return data + pad_len * '\0'
+
+
+def sa_in4(addr, port=0):
+    data = struct.pack("!H4s", port, addrconv.ipv4.text_to_bin(addr))
+    hdr = _hdr(_SIN_SIZE, socket.AF_INET)
+    return _pad_to(hdr + data, _SIN_SIZE)
+
+
+def sa_in6(addr, port=0, flowinfo=0, scope_id=0):
+    data = struct.pack("!HI16sI", port, flowinfo,
+                       addrconv.ipv6.text_to_bin(addr), scope_id)
+    hdr = _hdr(_HDR_LEN + len(data), socket.AF_INET6)
+    return hdr + data
+
+
+def sa_to_ss(sa):
+    return _pad_to(sa, _SS_MAXSIZE)
diff --git a/ryu/lib/sockopt.py b/ryu/lib/sockopt.py
new file mode 100644
index 00000000..6e533586
--- /dev/null
+++ b/ryu/lib/sockopt.py
@@ -0,0 +1,69 @@
+# Copyright (C) 2014 Nippon Telegraph and Telephone Corporation.
+# Copyright (C) 2014 YAMAMOTO Takashi <yamamoto at valinux co jp>
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import platform
+import socket
+import struct
+
+from ryu.lib import sockaddr
+
+
+def _set_tcp_md5sig_linux(s, addr, key):
+    # struct tcp_md5sig {
+    #     struct sockaddr_storage addr;
+    #     u16 pad1;
+    #     u16 keylen;
+    #     u32 pad2;
+    #     u8 key[80];
+    # }
+    TCP_MD5SIG = 14
+    af = s.family
+    if af == socket.AF_INET:
+        sa = sockaddr.sa_in4(addr)
+    elif af == socket.AF_INET6:
+        sa = sockaddr.sa_in6(addr)
+    else:
+        raise ValueError("unsupported af %s" % (af,))
+    ss = sockaddr.sa_to_ss(sa)
+    tcp_md5sig = ss + struct.pack("2xH4x80s", len(key), key)
+    s.setsockopt(socket.IPPROTO_TCP, TCP_MD5SIG, tcp_md5sig)
+
+
+def _set_tcp_md5sig_bsd(s, _addr, _key):
+    # NOTE: On this platform, address and key need to be set using setkey(8).
+    TCP_MD5SIG = 0x10
+    tcp_md5sig = struct.pack("I", 1)
+    s.setsockopt(socket.IPPROTO_TCP, TCP_MD5SIG, tcp_md5sig)
+
+
+def set_tcp_md5sig(s, addr, key):
+    """Enable TCP-MD5 on the given socket.
+
+    :param s: Socket
+    :param addr: Associated address.  On some platforms, this has no effect.
+    :param key: Key.  On some platforms, this has no effect.
+    """
+    impls = {
+        'FreeBSD': _set_tcp_md5sig_bsd,
+        'Linux': _set_tcp_md5sig_linux,
+        'NetBSD': _set_tcp_md5sig_bsd,
+    }
+    system = platform.system()
+    try:
+        impl = impls[system]
+    except KeyError:
+        raise NotImplementedError("TCP-MD5 unsupported on this platform")
+    impl(s, addr, key)