diff --git a/ryu/lib/packet/bfd.py b/ryu/lib/packet/bfd.py
index 05b0217c..8818da8e 100644
--- a/ryu/lib/packet/bfd.py
+++ b/ryu/lib/packet/bfd.py
@@ -511,8 +511,7 @@ class KeyedMD5(BFDAuth):
         auth_hdr_bin = self.serialize_hdr()
         auth_data_bin = struct.pack(self._PACK_STR, self.auth_key_id, 0,
                                     self.seq, self.auth_key +
-                                    ''.join(['\x00' *
-                                            (len(self.auth_key) - 16)]))
+                                    (b'\x00' * (len(self.auth_key) - 16)))
 
         h = hashlib.md5()
         h.update(bfd_bin + auth_hdr_bin + auth_data_bin)
@@ -551,7 +550,7 @@ class KeyedMD5(BFDAuth):
         auth_hdr_bin = self.serialize_hdr()
         auth_data_bin = struct.pack(self._PACK_STR, self.auth_key_id, 0,
                                     self.seq, auth_key +
-                                    ''.join(['\x00' * (len(auth_key) - 16)]))
+                                    (b'\x00' * (len(auth_key) - 16)))
 
         h = hashlib.md5()
         h.update(bfd_bin + auth_hdr_bin + auth_data_bin)
@@ -662,8 +661,7 @@ class KeyedSHA1(BFDAuth):
         auth_hdr_bin = self.serialize_hdr()
         auth_data_bin = struct.pack(self._PACK_STR, self.auth_key_id, 0,
                                     self.seq, self.auth_key +
-                                    ''.join(['\x00' *
-                                            (len(self.auth_key) - 20)]))
+                                    (b'\x00' * (len(self.auth_key) - 20)))
 
         h = hashlib.sha1()
         h.update(bfd_bin + auth_hdr_bin + auth_data_bin)
@@ -702,7 +700,7 @@ class KeyedSHA1(BFDAuth):
         auth_hdr_bin = self.serialize_hdr()
         auth_data_bin = struct.pack(self._PACK_STR, self.auth_key_id, 0,
                                     self.seq, auth_key +
-                                    ''.join(['\x00' * (len(auth_key) - 20)]))
+                                    (b'\x00' * (len(auth_key) - 20)))
 
         h = hashlib.sha1()
         h.update(bfd_bin + auth_hdr_bin + auth_data_bin)
diff --git a/ryu/lib/packet/bgp.py b/ryu/lib/packet/bgp.py
index 3de15676..623260fd 100644
--- a/ryu/lib/packet/bgp.py
+++ b/ryu/lib/packet/bgp.py
@@ -51,7 +51,7 @@ BGP_MSG_KEEPALIVE = 4
 BGP_MSG_ROUTE_REFRESH = 5  # RFC 2918
 
 _VERSION = 4
-_MARKER = 16 * '\xff'
+_MARKER = 16 * b'\xff'
 
 BGP_OPT_CAPABILITY = 2  # RFC 5492
 
diff --git a/ryu/lib/packet/cfm.py b/ryu/lib/packet/cfm.py
index 8e5717e5..e4544b19 100644
--- a/ryu/lib/packet/cfm.py
+++ b/ryu/lib/packet/cfm.py
@@ -260,9 +260,9 @@ class cc_message(operation):
     def __init__(self, md_lv=0, version=CFM_VERSION,
                  rdi=0, interval=_INTERVAL_1_SEC, seq_num=0, mep_id=1,
                  md_name_format=_MD_FMT_CHARACTER_STRING,
-                 md_name_length=0, md_name="0",
+                 md_name_length=0, md_name=b"0",
                  short_ma_name_format=_SHORT_MA_FMT_CHARACTER_STRING,
-                 short_ma_name_length=0, short_ma_name="1",
+                 short_ma_name_length=0, short_ma_name=b"1",
                  tlvs=None):
         super(cc_message, self).__init__(md_lv, version, tlvs)
         self._opcode = CFM_CC_MESSAGE
@@ -285,7 +285,7 @@ class cc_message(operation):
         (md_lv_version, opcode, flags, tlv_offset, seq_num, mep_id,
          md_name_format) = struct.unpack_from(cls._PACK_STR, buf)
         md_name_length = 0
-        md_name = ""
+        md_name = b""
         md_lv = int(md_lv_version >> 5)
         version = int(md_lv_version & 0x1f)
         rdi = int(flags >> 7)
@@ -310,9 +310,9 @@ class cc_message(operation):
         # ascii to text
         if md_name_format == cls._MD_FMT_DOMAIN_NAME_BASED_STRING or \
            md_name_format == cls._MD_FMT_CHARACTER_STRING:
-            md_name = "".join(map(chr, md_name))
+            md_name = b"".join(map(six.int2byte, md_name))
         if short_ma_name_format == cls._SHORT_MA_FMT_CHARACTER_STRING:
-            short_ma_name = "".join(map(chr, short_ma_name))
+            short_ma_name = b"".join(map(six.int2byte, short_ma_name))
         return cls(md_lv, version, rdi, interval, seq_num, mep_id,
                    md_name_format, md_name_length,
                    md_name,
@@ -925,7 +925,7 @@ class data_tlv(tlv):
     _PACK_STR = '!BH'
     _MIN_LEN = struct.calcsize(_PACK_STR)
 
-    def __init__(self, length=0, data_value=""
+    def __init__(self, length=0, data_value=b""
                  ):
         super(data_tlv, self).__init__(length)
         self._type = CFM_DATA_TLV
@@ -1171,9 +1171,9 @@ class organization_specific_tlv(tlv):
 
     def __init__(self,
                  length=0,
-                 oui="\x00\x00\x00",
+                 oui=b"\x00\x00\x00",
                  subtype=0,
-                 value=""
+                 value=b""
                  ):
         super(organization_specific_tlv, self).__init__(length)
         self._type = CFM_ORGANIZATION_SPECIFIC_TLV
@@ -1184,7 +1184,7 @@ class organization_specific_tlv(tlv):
     @classmethod
     def parser(cls, buf):
         (type_, length, oui, subtype) = struct.unpack_from(cls._PACK_STR, buf)
-        value = ""
+        value = b""
         if length > cls._OUI_AND_SUBTYPE_LEN:
             form = "%ds" % (length - cls._OUI_AND_SUBTYPE_LEN)
             (value,) = struct.unpack_from(form, buf, cls._MIN_LEN)
diff --git a/ryu/lib/packet/dhcp.py b/ryu/lib/packet/dhcp.py
index a172e790..bfc1f78c 100644
--- a/ryu/lib/packet/dhcp.py
+++ b/ryu/lib/packet/dhcp.py
@@ -149,7 +149,7 @@ class dhcp(packet_base.PacketBase):
     def __init__(self, op, chaddr, options, htype=_HARDWARE_TYPE_ETHERNET,
                  hlen=0, hops=0, xid=None, secs=0, flags=0,
                  ciaddr='0.0.0.0', yiaddr='0.0.0.0', siaddr='0.0.0.0',
-                 giaddr='0.0.0.0', sname='', boot_file=''):
+                 giaddr='0.0.0.0', sname=b'', boot_file=b''):
         super(dhcp, self).__init__()
         self.op = op
         self.htype = htype
diff --git a/ryu/lib/packet/ipv6.py b/ryu/lib/packet/ipv6.py
index 8d0a82eb..54f51e81 100644
--- a/ryu/lib/packet/ipv6.py
+++ b/ryu/lib/packet/ipv6.py
@@ -206,7 +206,7 @@ class opt_header(header):
         buf = bytearray(buf)
         if self.data is None:
             self.data = [option(type_=1, len_=4,
-                                data='\x00\x00\x00\x00')]
+                                data=b'\x00\x00\x00\x00')]
         for opt in self.data:
             buf.extend(opt.serialize())
         return buf
@@ -565,7 +565,7 @@ class auth(header):
     _MIN_LEN = struct.calcsize(_PACK_STR)
 
     def __init__(self, nxt=inet.IPPROTO_TCP, size=2, spi=0, seq=0,
-                 data='\x00\x00\x00\x00'):
+                 data=b'\x00\x00\x00\x00'):
         super(auth, self).__init__(nxt)
         assert data is not None
         self.size = size
diff --git a/ryu/lib/type_desc.py b/ryu/lib/type_desc.py
index 80d85bb2..cbe6f1ed 100644
--- a/ryu/lib/type_desc.py
+++ b/ryu/lib/type_desc.py
@@ -15,6 +15,8 @@
 # limitations under the License.
 
 
+import six
+
 from ryu.lib import addrconv
 
 
@@ -35,9 +37,9 @@ class IntDescr(TypeDescr):
         return i
 
     def from_user(self, i):
-        bin = ''
+        bin = b''
         for x in range(self.size):
-            bin = chr(i & 255) + bin
+            bin = six.int2byte(i & 255) + bin
             i //= 256
         return bin
 
diff --git a/ryu/tests/unit/packet/test_bfd.py b/ryu/tests/unit/packet/test_bfd.py
index d6c31134..c479ad96 100644
--- a/ryu/tests/unit/packet/test_bfd.py
+++ b/ryu/tests/unit/packet/test_bfd.py
@@ -85,7 +85,7 @@ class TestBFD(unittest.TestCase):
                               + '\x3c\xc1\x6a\x00\x69\x23'
 
         # BFD Key chain {auth_key_id: auth_key/password}
-        self.auth_keys = {2: "secret"}
+        self.auth_keys = {2: b"secret"}
 
     def tearDown(self):
         pass
diff --git a/ryu/tests/unit/packet/test_cfm.py b/ryu/tests/unit/packet/test_cfm.py
index 706e0be0..4120f875 100644
--- a/ryu/tests/unit/packet/test_cfm.py
+++ b/ryu/tests/unit/packet/test_cfm.py
@@ -44,10 +44,10 @@ class Test_cfm(unittest.TestCase):
         self.cc_message_mep_id = 4
         self.cc_message_md_name_format = 4
         self.cc_message_md_name_length = 0
-        self.cc_message_md_name = "hoge"
+        self.cc_message_md_name = b"hoge"
         self.cc_message_short_ma_name_format = 2
         self.cc_message_short_ma_name_length = 0
-        self.cc_message_short_ma_name = "pakeratta"
+        self.cc_message_short_ma_name = b"pakeratta"
         self.cc_message_md_name_txfcf = 11
         self.cc_message_md_name_rxfcb = 22
         self.cc_message_md_name_txfcb = 33
@@ -397,10 +397,10 @@ class Test_cc_message(unittest.TestCase):
         self.mep_id = 2
         self.md_name_format = cfm.cc_message._MD_FMT_CHARACTER_STRING
         self.md_name_length = 3
-        self.md_name = "foo"
+        self.md_name = b"foo"
         self.short_ma_name_format = 2
         self.short_ma_name_length = 8
-        self.short_ma_name = "hogehoge"
+        self.short_ma_name = b"hogehoge"
         self.tlvs = [
         ]
         self.end_tlv = 0
@@ -984,11 +984,11 @@ class Test_sender_id_tlv(unittest.TestCase):
         self.length = 10
         self.chassis_id_length = 1
         self.chassis_id_subtype = 3
-        self.chassis_id = "\x0a"
+        self.chassis_id = b"\x0a"
         self.ma_domain_length = 2
-        self.ma_domain = "\x04\x05"
+        self.ma_domain = b"\x04\x05"
         self.ma_length = 3
-        self.ma = "\x01\x02\x03"
+        self.ma = b"\x01\x02\x03"
         self.ins = cfm.sender_id_tlv(
             self.length,
             self.chassis_id_length,
@@ -1212,7 +1212,7 @@ class Test_data_tlv(unittest.TestCase):
     def setUp(self):
         self._type = cfm.CFM_DATA_TLV
         self.length = 3
-        self.data_value = "\x01\x02\x03"
+        self.data_value = b"\x01\x02\x03"
         self.ins = cfm.data_tlv(
             self.length,
             self.data_value
@@ -1495,9 +1495,9 @@ class Test_organization_specific_tlv(unittest.TestCase):
     def setUp(self):
         self._type = cfm.CFM_ORGANIZATION_SPECIFIC_TLV
         self.length = 10
-        self.oui = "\xff\x12\x34"
+        self.oui = b"\xff\x12\x34"
         self.subtype = 3
-        self.value = "\x01\x02\x0f\x0e\x0d\x0c"
+        self.value = b"\x01\x02\x0f\x0e\x0d\x0c"
         self.ins = cfm.organization_specific_tlv(self.length,
                                                  self.oui,
                                                  self.subtype,
@@ -1566,7 +1566,7 @@ class Test_organization_specific_tlv(unittest.TestCase):
                                  str(buf))
         eq_(res[0], cfm.CFM_ORGANIZATION_SPECIFIC_TLV)
         eq_(res[1], 4)
-        eq_(res[2], "\x00\x00\x00")
+        eq_(res[2], b"\x00\x00\x00")
         eq_(res[3], 0)
 
 
@@ -1579,7 +1579,7 @@ class Test_reply_ingress_tlv(unittest.TestCase):
         self.mac_address = 'aa:bb:cc:56:34:12'
         self.port_id_length = 3
         self.port_id_subtype = 2
-        self.port_id = "\x01\x04\x09"
+        self.port_id = b"\x01\x04\x09"
         self.ins = cfm.reply_ingress_tlv(self.length, self.action,
                                          self.mac_address,
                                          self.port_id_length,
@@ -1673,7 +1673,7 @@ class Test_reply_egress_tlv(unittest.TestCase):
         self.mac_address = 'aa:bb:cc:56:34:12'
         self.port_id_length = 3
         self.port_id_subtype = 2
-        self.port_id = "\x01\x04\x09"
+        self.port_id = b"\x01\x04\x09"
         self.ins = cfm.reply_egress_tlv(self.length,
                                         self.action,
                                         self.mac_address,
diff --git a/ryu/tests/unit/packet/test_dhcp.py b/ryu/tests/unit/packet/test_dhcp.py
index cd4e8c40..66b83d00 100644
--- a/ryu/tests/unit/packet/test_dhcp.py
+++ b/ryu/tests/unit/packet/test_dhcp.py
@@ -40,18 +40,18 @@ class Test_dhcp_offer(unittest.TestCase):
     yiaddr = '192.168.20.20'
     siaddr = '192.168.30.30'
     giaddr = '192.168.40.40'
-    sname = 'abc'
-    boot_file = ''
+    sname = b'abc'
+    boot_file = b''
 
     option_list = [
-        dhcp.option(dhcp.DHCP_MESSAGE_TYPE_OPT, '\x02', 1),
-        dhcp.option(dhcp.DHCP_SUBNET_MASK_OPT, '\xff\xff\xff\x00', 4),
-        dhcp.option(dhcp.DHCP_GATEWAY_ADDR_OPT, '\xc0\xa8\x0a\x09', 4),
-        dhcp.option(dhcp.DHCP_DNS_SERVER_ADDR_OPT, '\xc0\xa8\x0a\x09', 4),
-        dhcp.option(dhcp.DHCP_IP_ADDR_LEASE_TIME_OPT, '\x00\x03\xf4\x80', 4),
-        dhcp.option(dhcp.DHCP_RENEWAL_TIME_OPT, '\x00\x01\xfa\x40', 4),
-        dhcp.option(dhcp.DHCP_REBINDING_TIME_OPT, '\x00\x03\x75\xf0', 4),
-        dhcp.option(dhcp.DHCP_SERVER_IDENTIFIER_OPT, '\xc0\xa8\x0a\x09', 4)]
+        dhcp.option(dhcp.DHCP_MESSAGE_TYPE_OPT, b'\x02', 1),
+        dhcp.option(dhcp.DHCP_SUBNET_MASK_OPT, b'\xff\xff\xff\x00', 4),
+        dhcp.option(dhcp.DHCP_GATEWAY_ADDR_OPT, b'\xc0\xa8\x0a\x09', 4),
+        dhcp.option(dhcp.DHCP_DNS_SERVER_ADDR_OPT, b'\xc0\xa8\x0a\x09', 4),
+        dhcp.option(dhcp.DHCP_IP_ADDR_LEASE_TIME_OPT, b'\x00\x03\xf4\x80', 4),
+        dhcp.option(dhcp.DHCP_RENEWAL_TIME_OPT, b'\x00\x01\xfa\x40', 4),
+        dhcp.option(dhcp.DHCP_REBINDING_TIME_OPT, b'\x00\x03\x75\xf0', 4),
+        dhcp.option(dhcp.DHCP_SERVER_IDENTIFIER_OPT, b'\xc0\xa8\x0a\x09', 4)]
     magic_cookie = '99.130.83.99'
     options = dhcp.options(option_list=option_list, options_len=50,
                            magic_cookie=magic_cookie)
@@ -61,24 +61,24 @@ class Test_dhcp_offer(unittest.TestCase):
                    ciaddr=ciaddr, yiaddr=yiaddr, siaddr=siaddr,
                    giaddr=giaddr, sname=sname, boot_file=boot_file)
 
-    buf = "\x02\x01\x06\x00\x00\x00\x00\x01\x00\x00\x00\x01\xc0\xa8\x0a\x0a"\
-        + "\xc0\xa8\x14\x14\xc0\xa8\x1e\x1e\xc0\xa8\x28\x28\xaa\xaa\xaa\xaa"\
-        + "\xaa\xaa\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x61\x62\x63\x00"\
-        + "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
-        + "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
-        + "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
-        + "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
-        + "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
-        + "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
-        + "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
-        + "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
-        + "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
-        + "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
-        + "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
-        + "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x63\x82\x53\x63"\
-        + "\x35\x01\x02\x01\x04\xff\xff\xff\x00\x03\x04\xc0\xa8\x0a\x09\x06"\
-        + "\x04\xc0\xa8\x0a\x09\x33\x04\x00\x03\xf4\x80\x3a\x04\x00\x01\xfa"\
-        + "\x40\x3b\x04\x00\x03\x75\xf0\x36\x04\xc0\xa8\x0a\x09\xff"
+    buf = b"\x02\x01\x06\x00\x00\x00\x00\x01\x00\x00\x00\x01\xc0\xa8\x0a\x0a"\
+        + b"\xc0\xa8\x14\x14\xc0\xa8\x1e\x1e\xc0\xa8\x28\x28\xaa\xaa\xaa\xaa"\
+        + b"\xaa\xaa\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x61\x62\x63\x00"\
+        + b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
+        + b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
+        + b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
+        + b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
+        + b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
+        + b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
+        + b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
+        + b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
+        + b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
+        + b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
+        + b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"\
+        + b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x63\x82\x53\x63"\
+        + b"\x35\x01\x02\x01\x04\xff\xff\xff\x00\x03\x04\xc0\xa8\x0a\x09\x06"\
+        + b"\x04\xc0\xa8\x0a\x09\x33\x04\x00\x03\xf4\x80\x3a\x04\x00\x01\xfa"\
+        + b"\x40\x3b\x04\x00\x03\x75\xf0\x36\x04\xc0\xa8\x0a\x09\xff"
 
     def setUp(self):
         pass
diff --git a/ryu/tests/unit/packet/test_ipv6.py b/ryu/tests/unit/packet/test_ipv6.py
index 805c3dcf..d9bdf291 100644
--- a/ryu/tests/unit/packet/test_ipv6.py
+++ b/ryu/tests/unit/packet/test_ipv6.py
@@ -57,7 +57,7 @@ class Test_ipv6(unittest.TestCase):
     def setUp_with_hop_opts(self):
         self.opt1_type = 5
         self.opt1_len = 2
-        self.opt1_data = '\x00\x00'
+        self.opt1_data = b'\x00\x00'
         self.opt2_type = 1
         self.opt2_len = 0
         self.opt2_data = None
@@ -86,7 +86,7 @@ class Test_ipv6(unittest.TestCase):
     def setUp_with_dst_opts(self):
         self.opt1_type = 5
         self.opt1_len = 2
-        self.opt1_data = '\x00\x00'
+        self.opt1_data = b'\x00\x00'
         self.opt2_type = 1
         self.opt2_len = 0
         self.opt2_data = None
@@ -167,7 +167,7 @@ class Test_ipv6(unittest.TestCase):
         self.auth_size = 4
         self.auth_spi = 256
         self.auth_seq = 1
-        self.auth_data = '\xa0\xe7\xf8\xab\xf9\x69\x1a\x8b\xf3\x9f\x7c\xae'
+        self.auth_data = b'\xa0\xe7\xf8\xab\xf9\x69\x1a\x8b\xf3\x9f\x7c\xae'
         self.auth = ipv6.auth(
             self.auth_nxt, self.auth_size, self.auth_spi, self.auth_seq,
             self.auth_data)
@@ -188,7 +188,7 @@ class Test_ipv6(unittest.TestCase):
     def setUp_with_multi_headers(self):
         self.opt1_type = 5
         self.opt1_len = 2
-        self.opt1_data = '\x00\x00'
+        self.opt1_data = b'\x00\x00'
         self.opt2_type = 1
         self.opt2_len = 0
         self.opt2_data = None
@@ -204,7 +204,7 @@ class Test_ipv6(unittest.TestCase):
         self.auth_size = 4
         self.auth_spi = 256
         self.auth_seq = 1
-        self.auth_data = '\xa0\xe7\xf8\xab\xf9\x69\x1a\x8b\xf3\x9f\x7c\xae'
+        self.auth_data = b'\xa0\xe7\xf8\xab\xf9\x69\x1a\x8b\xf3\x9f\x7c\xae'
         self.auth = ipv6.auth(
             self.auth_nxt, self.auth_size, self.auth_spi, self.auth_seq,
             self.auth_data)
@@ -510,9 +510,9 @@ class Test_hop_opts(unittest.TestCase):
         self.nxt = 0
         self.size = 8
         self.data = [
-            ipv6.option(5, 2, '\x00\x00'),
+            ipv6.option(5, 2, b'\x00\x00'),
             ipv6.option(1, 0, None),
-            ipv6.option(0xc2, 4, '\x00\x01\x00\x00'),
+            ipv6.option(0xc2, 4, b'\x00\x01\x00\x00'),
             ipv6.option(1, 0, None),
         ]
         self.hop = ipv6.hop_opts(self.nxt, self.size, self.data)
@@ -591,9 +591,9 @@ class Test_dst_opts(unittest.TestCase):
         self.nxt = 60
         self.size = 8
         self.data = [
-            ipv6.option(5, 2, '\x00\x00'),
+            ipv6.option(5, 2, b'\x00\x00'),
             ipv6.option(1, 0, None),
-            ipv6.option(0xc2, 4, '\x00\x01\x00\x00'),
+            ipv6.option(0xc2, 4, b'\x00\x01\x00\x00'),
             ipv6.option(1, 0, None),
         ]
         self.dst = ipv6.dst_opts(self.nxt, self.size, self.data)
@@ -662,7 +662,7 @@ class Test_dst_opts(unittest.TestCase):
 
         eq_(res[0], 6)
         eq_(res[1], 0)
-        opt = ipv6.option(type_=1, len_=4, data='\x00\x00\x00\x00')
+        opt = ipv6.option(type_=1, len_=4, data=b'\x00\x00\x00\x00')
         eq_(str(buf[2:]), opt.serialize())
 
 
@@ -670,7 +670,7 @@ class Test_option(unittest.TestCase):
 
     def setUp(self):
         self.type_ = 5
-        self.data = '\x00\x00'
+        self.data = b'\x00\x00'
         self.len_ = len(self.data)
         self.opt = ipv6.option(self.type_, self.len_, self.data)
         self.form = '!BB%ds' % self.len_
@@ -1068,7 +1068,7 @@ class Test_auth(unittest.TestCase):
         self.size = 4
         self.spi = 256
         self.seq = 1
-        self.data = '\x21\xd3\xa9\x5c\x5f\xfd\x4d\x18\x46\x22\xb9\xf8'
+        self.data = b'\x21\xd3\xa9\x5c\x5f\xfd\x4d\x18\x46\x22\xb9\xf8'
         self.auth = ipv6.auth(
             self.nxt, self.size, self.spi, self.seq, self.data)
         self.form = '!BB2xII12s'