diff --git a/ryu/lib/bfdlib.py b/ryu/lib/bfdlib.py
index c34e6a46..46696929 100644
--- a/ryu/lib/bfdlib.py
+++ b/ryu/lib/bfdlib.py
@@ -34,6 +34,7 @@ Please note that:
 
 
 import logging
+import six
 import time
 import random
 
@@ -228,7 +229,7 @@ class BFDSession(object):
         BFD packet receiver.
         """
         LOG.debug("[BFD][%s][RECV] BFD Control received: %s",
-                  hex(self._local_discr), str(bfd_pkt))
+                  hex(self._local_discr), six.binary_type(bfd_pkt))
         self._remote_discr = bfd_pkt.my_discr
         self._remote_state = bfd_pkt.state
         self._remote_demand_mode = bfd_pkt.flags & bfd.BFD_FLAG_DEMAND
diff --git a/ryu/lib/pcaplib.py b/ryu/lib/pcaplib.py
index 62812b21..03e02027 100644
--- a/ryu/lib/pcaplib.py
+++ b/ryu/lib/pcaplib.py
@@ -66,6 +66,7 @@ Sample usage of reading PCAP files:
 
 """
 
+import six
 import struct
 import sys
 import time
@@ -279,7 +280,7 @@ class Writer(object):
         if ts is None:
             ts = time.time()
 
-        buf_str = str(buf)
+        buf_str = six.binary_type(buf)
         buf_str_len = len(buf_str)
         self._write_pkt_hdr(ts, buf_str_len)
         self._f.write(buf_str)
diff --git a/ryu/lib/snortlib.py b/ryu/lib/snortlib.py
index 495364aa..803eb452 100644
--- a/ryu/lib/snortlib.py
+++ b/ryu/lib/snortlib.py
@@ -16,6 +16,7 @@
 
 import os
 import logging
+import six
 
 from ryu.lib import hub, alert
 from ryu.base import app_manager
@@ -92,7 +93,7 @@ class SnortLib(app_manager.RyuApp):
             hub.spawn(self._recv_loop_nw_sock, conn, addr)
 
     def _recv_loop_nw_sock(self, conn, addr):
-        buf = str()
+        buf = six.binary_type()
         while True:
             ret = conn.recv(BUFSIZE)
             if len(ret) == 0:
diff --git a/ryu/tests/unit/ofproto/test_parser_v10.py b/ryu/tests/unit/ofproto/test_parser_v10.py
index e37f51a9..1895f65a 100644
--- a/ryu/tests/unit/ofproto/test_parser_v10.py
+++ b/ryu/tests/unit/ofproto/test_parser_v10.py
@@ -17,6 +17,7 @@
 
 import unittest
 import logging
+import six
 from nose.tools import *
 from ryu.ofproto.ofproto_v1_0_parser import *
 from ryu.ofproto import ofproto_v1_0_parser
@@ -45,7 +46,7 @@ class TestOFPPhyPort(unittest.TestCase):
 
     buf = port_no['buf'] \
         + addrconv.mac.text_to_bin(hw_addr) \
-        + name \
+        + str.encode(name, 'ascii') \
         + config['buf'] \
         + state['buf'] \
         + curr['buf'] \
@@ -2303,7 +2304,7 @@ class TestOFPTableStats(unittest.TestCase):
 
     buf = table_id['buf'] \
         + zfill \
-        + name \
+        + str.encode(name, 'ascii') \
         + wildcards['buf'] \
         + max_entries['buf'] \
         + active_count['buf'] \
@@ -2781,7 +2782,7 @@ class TestOFPErrorMsg(unittest.TestCase):
             + ofproto.OFP_ERROR_MSG_PACK_STR.replace('!', '') \
             + str(len(data)) + 's'
 
-        res = struct.unpack(fmt, str(c.buf))
+        res = struct.unpack(fmt, six.binary_type(c.buf))
         eq_(ofproto.OFP_VERSION, res[0])
         eq_(ofproto.OFPT_ERROR, res[1])
         eq_(len(c.buf), res[2])
@@ -2851,7 +2852,7 @@ class TestOFPEchoRequest(unittest.TestCase):
             + ofproto.OFP_HEADER_PACK_STR.replace('!', '') \
             + str(len(data)) + 's'
 
-        res = struct.unpack(fmt, str(c.buf))
+        res = struct.unpack(fmt, six.binary_type(c.buf))
         eq_(ofproto.OFP_VERSION, res[0])
         eq_(ofproto.OFPT_ECHO_REQUEST, res[1])
         eq_(len(c.buf), res[2])
@@ -2919,7 +2920,7 @@ class TestOFPEchoReply(unittest.TestCase):
             + ofproto.OFP_HEADER_PACK_STR.replace('!', '') \
             + str(len(data)) + 's'
 
-        res = struct.unpack(fmt, str(c.buf))
+        res = struct.unpack(fmt, six.binary_type(c.buf))
         eq_(ofproto.OFP_VERSION, res[0])
         eq_(ofproto.OFPT_ECHO_REPLY, res[1])
         eq_(len(c.buf), res[2])
@@ -2994,7 +2995,7 @@ class TestOFPVendor(unittest.TestCase):
             + ofproto.OFP_VENDOR_HEADER_PACK_STR.replace('!', '') \
             + str(len(data)) + 's'
 
-        res = struct.unpack(fmt, str(c.buf))
+        res = struct.unpack(fmt, six.binary_type(c.buf))
         eq_(ofproto.OFP_VERSION, res[0])
         eq_(ofproto.OFPT_VENDOR, res[1])
         eq_(len(c.buf), res[2])
@@ -3047,7 +3048,7 @@ class TestNiciraHeader(unittest.TestCase):
             + ofproto.NICIRA_HEADER_PACK_STR.replace('!', '') \
             + str(len(data)) + 's'
 
-        res = struct.unpack(fmt, str(c.buf))
+        res = struct.unpack(fmt, six.binary_type(c.buf))
         eq_(ofproto.OFP_VERSION, res[0])
         eq_(ofproto.OFPT_VENDOR, res[1])
         eq_(len(c.buf), res[2])
@@ -3097,7 +3098,7 @@ class TestNXTSetFlowFormat(unittest.TestCase):
             + ofproto.NICIRA_HEADER_PACK_STR.replace('!', '') \
             + ofproto.NX_SET_FLOW_FORMAT_PACK_STR.replace('!', '')
 
-        res = struct.unpack(fmt, str(c.buf))
+        res = struct.unpack(fmt, six.binary_type(c.buf))
         eq_(ofproto.OFP_VERSION, res[0])
         eq_(ofproto.OFPT_VENDOR, res[1])
         eq_(len(c.buf), res[2])
@@ -3197,7 +3198,7 @@ class TestNXTFlowMod(unittest.TestCase):
             + ofproto.NICIRA_HEADER_PACK_STR.replace('!', '') \
             + ofproto.NX_FLOW_MOD_PACK_STR.replace('!', '')
 
-        res = struct.unpack(fmt, str(c.buf))
+        res = struct.unpack(fmt, six.binary_type(c.buf))
         eq_(ofproto.OFP_VERSION, res[0])
         eq_(ofproto.OFPT_VENDOR, res[1])
         eq_(len(c.buf), res[2])
@@ -3228,7 +3229,7 @@ class TestNXTFlowMod(unittest.TestCase):
             + ofproto.NX_FLOW_MOD_PACK_STR.replace('!', '') \
             + ofproto.OFP_ACTION_OUTPUT_PACK_STR.replace('!', '')
 
-        res = struct.unpack(fmt, str(c.buf))
+        res = struct.unpack(fmt, six.binary_type(c.buf))
         eq_(ofproto.OFP_VERSION, res[0])
         eq_(ofproto.OFPT_VENDOR, res[1])
         eq_(len(c.buf), res[2])
@@ -3292,7 +3293,7 @@ class TestNXTRoleRequest(unittest.TestCase):
             + ofproto.NICIRA_HEADER_PACK_STR.replace('!', '') \
             + ofproto.NX_ROLE_PACK_STR.replace('!', '')
 
-        res = struct.unpack(fmt, str(self.c.buf))
+        res = struct.unpack(fmt, six.binary_type(self.c.buf))
 
         eq_(ofproto.OFP_VERSION, res[0])
         eq_(ofproto.OFPT_VENDOR, res[1])
@@ -3344,7 +3345,7 @@ class TestNXTFlowModTableId(unittest.TestCase):
             + ofproto.NICIRA_HEADER_PACK_STR.replace('!', '') \
             + ofproto.NX_FLOW_MOD_TABLE_ID_PACK_STR.replace('!', '')
 
-        res = struct.unpack(fmt, str(self.c.buf))
+        res = struct.unpack(fmt, six.binary_type(self.c.buf))
         eq_(ofproto.OFP_VERSION, res[0])
         eq_(ofproto.OFPT_VENDOR, res[1])
         eq_(len(self.c.buf), res[2])
@@ -4660,7 +4661,7 @@ class TestOFPFeaturesRequest(unittest.TestCase):
 
         fmt = ofproto.OFP_HEADER_PACK_STR
 
-        res = struct.unpack(fmt, str(self.c.buf))
+        res = struct.unpack(fmt, six.binary_type(self.c.buf))
         eq_(ofproto.OFP_VERSION, res[0])
         eq_(ofproto.OFPT_FEATURES_REQUEST, res[1])
         eq_(len(self.c.buf), res[2])
@@ -4699,7 +4700,7 @@ class TestOFPGetConfigRequest(unittest.TestCase):
 
         fmt = ofproto.OFP_HEADER_PACK_STR
 
-        res = struct.unpack(fmt, str(self.c.buf))
+        res = struct.unpack(fmt, six.binary_type(self.c.buf))
         eq_(ofproto.OFP_VERSION, res[0])
         eq_(ofproto.OFPT_GET_CONFIG_REQUEST, res[1])
         eq_(len(self.c.buf), res[2])
@@ -4748,7 +4749,7 @@ class TestOFPSetConfig(unittest.TestCase):
             + ofproto.OFP_HEADER_PACK_STR.replace('!', '') \
             + ofproto.OFP_SWITCH_CONFIG_PACK_STR.replace('!', '')
 
-        res = struct.unpack(fmt, str(self.c.buf))
+        res = struct.unpack(fmt, six.binary_type(self.c.buf))
         eq_(ofproto.OFP_VERSION, res[0])
         eq_(ofproto.OFPT_SET_CONFIG, res[1])
         eq_(len(self.c.buf), res[2])
@@ -4815,7 +4816,7 @@ class TestOFPPacketOut(unittest.TestCase):
             + ofproto.OFP_ACTION_OUTPUT_PACK_STR.replace('!', '') \
             + str(len(data)) + 's'
 
-        res = struct.unpack(fmt, str(c.buf))
+        res = struct.unpack(fmt, six.binary_type(c.buf))
 
         # OFP_HEADER_PACK_STR
         eq_(ofproto.OFP_VERSION, res[0])
@@ -4962,7 +4963,7 @@ class TestOFPFlowMod(unittest.TestCase):
             + ofproto.OFP_FLOW_MOD_PACK_STR0.replace('!', '') \
             + ofproto.OFP_ACTION_OUTPUT_PACK_STR.replace('!', '')
 
-        res = struct.unpack(fmt, str(c.buf))
+        res = struct.unpack(fmt, six.binary_type(c.buf))
 
         # OFP_HEADER_PACK_STR
         eq_(ofproto.OFP_VERSION, res[0])
@@ -5034,7 +5035,7 @@ class TestOFPBarrierRequest(unittest.TestCase):
 
         fmt = ofproto.OFP_HEADER_PACK_STR
 
-        res = struct.unpack(fmt, str(self.c.buf))
+        res = struct.unpack(fmt, six.binary_type(self.c.buf))
         eq_(ofproto.OFP_VERSION, res[0])
         eq_(ofproto.OFPT_BARRIER_REQUEST, res[1])
         eq_(len(self.c.buf), res[2])
@@ -5081,7 +5082,7 @@ class TestOFPQueueGetConfigRequest(unittest.TestCase):
         b = ofproto.OFP_QUEUE_GET_CONFIG_REQUEST_PACK_STR.replace('!', '')
         fmt = '!' + a + b
 
-        res = struct.unpack(fmt, str(self.c.buf))
+        res = struct.unpack(fmt, six.binary_type(self.c.buf))
         eq_(ofproto.OFP_VERSION, res[0])
         eq_(ofproto.OFPT_QUEUE_GET_CONFIG_REQUEST, res[1])
         eq_(len(self.c.buf), res[2])
@@ -5126,7 +5127,7 @@ class TestOFPDescStatsRequest(unittest.TestCase):
             + ofproto.OFP_HEADER_PACK_STR.replace('!', '') \
             + ofproto.OFP_STATS_MSG_PACK_STR.replace('!', '')
 
-        res = struct.unpack(fmt, str(self.c.buf))
+        res = struct.unpack(fmt, six.binary_type(self.c.buf))
 
         # OFP_HEADER_PACK_STR
         eq_(ofproto.OFP_VERSION, res[0])
@@ -5228,7 +5229,7 @@ class TestOFPFlowStatsRequest(unittest.TestCase):
             + ofproto.OFP_MATCH_PACK_STR.replace('!', '') \
             + ofproto.OFP_FLOW_STATS_REQUEST_ID_PORT_STR.replace('!', '')
 
-        res = struct.unpack(fmt, str(self.c.buf))
+        res = struct.unpack(fmt, six.binary_type(self.c.buf))
 
         # OFP_HEADER_PACK_STR
         eq_(ofproto.OFP_VERSION, res[0])
@@ -5349,7 +5350,7 @@ class TestOFPAggregateStatsRequest(unittest.TestCase):
             + ofproto.OFP_MATCH_PACK_STR.replace('!', '') \
             + ofproto.OFP_FLOW_STATS_REQUEST_ID_PORT_STR.replace('!', '')
 
-        res = struct.unpack(fmt, str(self.c.buf))
+        res = struct.unpack(fmt, six.binary_type(self.c.buf))
 
         # OFP_HEADER_PACK_STR
         eq_(ofproto.OFP_VERSION, res[0])
@@ -5418,7 +5419,7 @@ class TestOFPTableStatsRequest(unittest.TestCase):
             + ofproto.OFP_HEADER_PACK_STR.replace('!', '') \
             + ofproto.OFP_STATS_MSG_PACK_STR.replace('!', '')
 
-        res = struct.unpack(fmt, str(self.c.buf))
+        res = struct.unpack(fmt, six.binary_type(self.c.buf))
 
         # OFP_HEADER_PACK_STR
         eq_(ofproto.OFP_VERSION, res[0])
@@ -5476,7 +5477,7 @@ class TestOFPPortStatsRequest(unittest.TestCase):
             + ofproto.OFP_STATS_MSG_PACK_STR.replace('!', '') \
             + ofproto.OFP_PORT_STATS_REQUEST_PACK_STR.replace('!', '')
 
-        res = struct.unpack(fmt, str(self.c.buf))
+        res = struct.unpack(fmt, six.binary_type(self.c.buf))
 
         # OFP_HEADER_PACK_STR
         eq_(ofproto.OFP_VERSION, res[0])
@@ -5540,7 +5541,7 @@ class TestOFPQueueStatsRequest(unittest.TestCase):
             + ofproto.OFP_STATS_MSG_PACK_STR.replace('!', '') \
             + ofproto.OFP_QUEUE_STATS_REQUEST_PACK_STR.replace('!', '')
 
-        res = struct.unpack(fmt, str(self.c.buf))
+        res = struct.unpack(fmt, six.binary_type(self.c.buf))
 
         # OFP_HEADER_PACK_STR
         eq_(ofproto.OFP_VERSION, res[0])
@@ -5607,7 +5608,7 @@ class TestOFPVendorStatsRequest(unittest.TestCase):
             + ofproto.OFP_VENDOR_STATS_MSG_PACK_STR.replace('!', '') \
             + str(len(self.specific_data)) + 's'
 
-        res = struct.unpack(fmt, str(self.c.buf))
+        res = struct.unpack(fmt, six.binary_type(self.c.buf))
 
         # OFP_HEADER_PACK_STR
         eq_(ofproto.OFP_VERSION, res[0])