diff --git a/ryu/lib/ofp_pktinfilter.py b/ryu/lib/ofp_pktinfilter.py
index c3bd9797..a84f7bb4 100644
--- a/ryu/lib/ofp_pktinfilter.py
+++ b/ryu/lib/ofp_pktinfilter.py
@@ -16,6 +16,7 @@
 
 import logging
 from abc import ABCMeta, abstractmethod
+import six
 
 from ryu.lib.packet import packet
 
@@ -36,9 +37,8 @@ def packet_in_filter(cls, args=None):
     return _packet_in_filter
 
 
+@six.add_metaclass(ABCMeta)
 class PacketInFilterBase(object):
-    __metaclass__ = ABCMeta
-
     def __init__(self, args):
         self.args = args
 
diff --git a/ryu/lib/packet/bgp.py b/ryu/lib/packet/bgp.py
index 6c1d6ad7..2d71917c 100644
--- a/ryu/lib/packet/bgp.py
+++ b/ryu/lib/packet/bgp.py
@@ -23,6 +23,7 @@ RFC 4271 BGP-4
 # - RFC 4364 BGP/MPLS IP Virtual Private Networks (VPNs)
 
 import abc
+import six
 import struct
 
 from ryu.ofproto.ofproto_parser import msg_pack_into
@@ -137,8 +138,8 @@ def pad(bin, len_):
     return bin + (len_ - len(bin)) * '\0'
 
 
+@six.add_metaclass(abc.ABCMeta)
 class _AddrPrefix(StringifyMixin):
-    __metaclass__ = abc.ABCMeta
     _PACK_STR = '!B'  # length
 
     def __init__(self, length, addr, prefixes=None):
diff --git a/ryu/lib/packet/icmpv6.py b/ryu/lib/packet/icmpv6.py
index 4ba1d63d..c36ad04a 100644
--- a/ryu/lib/packet/icmpv6.py
+++ b/ryu/lib/packet/icmpv6.py
@@ -15,6 +15,7 @@
 
 import abc
 import struct
+import six
 import sys
 import array
 import binascii
@@ -387,10 +388,8 @@ class nd_router_advert(stringify.StringifyMixin):
         return length
 
 
+@six.add_metaclass(abc.ABCMeta)
 class nd_option(stringify.StringifyMixin):
-
-    __metaclass__ = abc.ABCMeta
-
     @classmethod
     @abc.abstractmethod
     def option_type(cls):
diff --git a/ryu/lib/packet/ipv6.py b/ryu/lib/packet/ipv6.py
index 1c481b5c..960f1acb 100644
--- a/ryu/lib/packet/ipv6.py
+++ b/ryu/lib/packet/ipv6.py
@@ -14,6 +14,7 @@
 # limitations under the License.
 
 import abc
+import six
 import struct
 from . import packet_base
 from . import icmpv6
@@ -147,11 +148,9 @@ ipv6.register_packet_type(udp.udp, inet.IPPROTO_UDP)
 ipv6.register_packet_type(sctp.sctp, inet.IPPROTO_SCTP)
 
 
+@six.add_metaclass(abc.ABCMeta)
 class header(stringify.StringifyMixin):
     """extension header abstract class."""
-
-    __metaclass__ = abc.ABCMeta
-
     def __init__(self, nxt):
         self.nxt = nxt
 
diff --git a/ryu/lib/packet/packet_base.py b/ryu/lib/packet/packet_base.py
index cbc213fd..f08330b9 100644
--- a/ryu/lib/packet/packet_base.py
+++ b/ryu/lib/packet/packet_base.py
@@ -14,12 +14,13 @@
 # limitations under the License.
 
 import abc
+import six
 from ryu.lib import stringify
 
 
+@six.add_metaclass(abc.ABCMeta)
 class PacketBase(stringify.StringifyMixin):
     """A base class for a protocol (ethernet, ipv4, ...) header."""
-    __metaclass__ = abc.ABCMeta
     _TYPES = {}
 
     @classmethod
diff --git a/ryu/lib/packet/sctp.py b/ryu/lib/packet/sctp.py
index e984dc21..88d9d37e 100644
--- a/ryu/lib/packet/sctp.py
+++ b/ryu/lib/packet/sctp.py
@@ -14,6 +14,7 @@
 # limitations under the License.
 
 import abc
+import six
 import struct
 
 from ryu.lib import addrconv
@@ -227,9 +228,8 @@ class sctp(packet_base.PacketBase):
 # Chunk Types
 #
 #=======================================================================
+@six.add_metaclass(abc.ABCMeta)
 class chunk(stringify.StringifyMixin):
-
-    __metaclass__ = abc.ABCMeta
     _PACK_STR = '!BBH'
     _MIN_LEN = struct.calcsize(_PACK_STR)
 
@@ -252,9 +252,8 @@ class chunk(stringify.StringifyMixin):
         return self.length
 
 
+@six.add_metaclass(abc.ABCMeta)
 class chunk_init_base(chunk):
-
-    __metaclass__ = abc.ABCMeta
     _PACK_STR = '!BBHIIHHI'
     _MIN_LEN = struct.calcsize(_PACK_STR)
     _class_prefixes = ['param_']
@@ -304,9 +303,8 @@ class chunk_init_base(chunk):
         return str(buf)
 
 
+@six.add_metaclass(abc.ABCMeta)
 class chunk_heartbeat_base(chunk):
-
-    __metaclass__ = abc.ABCMeta
     _class_prefixes = ['param_']
 
     def __init__(self, flags=0, length=0, info=None):
@@ -338,10 +336,8 @@ class chunk_heartbeat_base(chunk):
         return str(buf)
 
 
+@six.add_metaclass(abc.ABCMeta)
 class chunk_ack_base(chunk):
-
-    __metaclass__ = abc.ABCMeta
-
     def __init__(self, flags=0, length=0):
         super(chunk_ack_base, self).__init__(self.chunk_type(), length)
         self.flags = flags
@@ -360,9 +356,8 @@ class chunk_ack_base(chunk):
         return buf
 
 
+@six.add_metaclass(abc.ABCMeta)
 class chunk_ecn_base(chunk):
-
-    __metaclass__ = abc.ABCMeta
     _PACK_STR = '!BBHI'
     _MIN_LEN = struct.calcsize(_PACK_STR)
 
@@ -1176,9 +1171,8 @@ class chunk_shutdown_complete(chunk):
 # Cause Code
 #
 #=======================================================================
+@six.add_metaclass(abc.ABCMeta)
 class cause(stringify.StringifyMixin):
-
-    __metaclass__ = abc.ABCMeta
     _PACK_STR = '!HH'
     _MIN_LEN = struct.calcsize(_PACK_STR)
 
@@ -1210,10 +1204,8 @@ class cause(stringify.StringifyMixin):
         return length
 
 
+@six.add_metaclass(abc.ABCMeta)
 class cause_with_value(cause):
-
-    __metaclass__ = abc.ABCMeta
-
     def __init__(self, value=None, length=0):
         super(cause_with_value, self).__init__(length)
         self.value = value
@@ -1777,9 +1769,8 @@ class cause_protocol_violation(cause_with_value):
 # Chunk Parameter Types
 #
 #=======================================================================
+@six.add_metaclass(abc.ABCMeta)
 class param(stringify.StringifyMixin):
-
-    __metaclass__ = abc.ABCMeta
     _PACK_STR = '!HH'
     _MIN_LEN = struct.calcsize(_PACK_STR)
 
diff --git a/ryu/lib/packet/stream_parser.py b/ryu/lib/packet/stream_parser.py
index 87e1aed6..75e6cc53 100644
--- a/ryu/lib/packet/stream_parser.py
+++ b/ryu/lib/packet/stream_parser.py
@@ -16,8 +16,10 @@
 
 
 from abc import ABCMeta, abstractmethod
+import six
 
 
+@six.add_metaclass(ABCMeta)
 class StreamParser(object):
     """Streaming parser base class.
 
@@ -29,9 +31,6 @@ class StreamParser(object):
     is TCP.
 
     """
-
-    __metaclass__ = ABCMeta
-
     class TooSmallException(Exception):
         pass
 
diff --git a/ryu/lib/packet/vlan.py b/ryu/lib/packet/vlan.py
index 1ee7dd38..a4f4332c 100644
--- a/ryu/lib/packet/vlan.py
+++ b/ryu/lib/packet/vlan.py
@@ -14,6 +14,7 @@
 # limitations under the License.
 
 import abc
+import six
 import struct
 from . import packet_base
 from . import arp
@@ -26,9 +27,8 @@ from . import pbb
 from ryu.ofproto import ether
 
 
+@six.add_metaclass(abc.ABCMeta)
 class _vlan(packet_base.PacketBase):
-
-    __metaclass__ = abc.ABCMeta
     _PACK_STR = "!HH"
     _MIN_LEN = struct.calcsize(_PACK_STR)
 
diff --git a/ryu/services/protocols/vrrp/router.py b/ryu/services/protocols/vrrp/router.py
index ff2290d5..610a67b4 100644
--- a/ryu/services/protocols/vrrp/router.py
+++ b/ryu/services/protocols/vrrp/router.py
@@ -21,6 +21,7 @@ VRRPManager creates/deletes VRRPRounter instances dynamically.
 """
 
 import abc
+import six
 
 from ryu.base import app_manager
 from ryu.controller import event
@@ -103,9 +104,8 @@ class VRRPParams(object):
         return (3.0 * self.master_adver_interval) + self.skew_time
 
 
+@six.add_metaclass(abc.ABCMeta)
 class VRRPState(object):
-    __metaclass__ = abc.ABCMeta
-
     def __init__(self, vrrp_router):
         super(VRRPState, self).__init__()
         self.vrrp_router = vrrp_router
diff --git a/tools/pip-requires b/tools/pip-requires
index 565e4d42..96315d00 100644
--- a/tools/pip-requires
+++ b/tools/pip-requires
@@ -5,4 +5,5 @@ netaddr
 oslo.config
 paramiko
 routes
+six
 webob>=1.0.8