diff --git a/test/functional/test_framework/netutil.py b/test/functional/test_framework/netutil.py
index 2d08ba4e4d..5f898ec968 100644
--- a/test/functional/test_framework/netutil.py
+++ b/test/functional/test_framework/netutil.py
@@ -1,168 +1,168 @@
 #!/usr/bin/env python3
 # Copyright (c) 2014-2016 The Bitcoin Core developers
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Linux network utilities.
 
 Roughly based on http://voorloopnul.com/blog/a-python-netstat-in-less-than-100-lines-of-code/ by Ricardo Pascal
 """
 
 import sys
 import socket
 import fcntl
 import struct
 import array
 import os
 from binascii import unhexlify, hexlify
 
 # STATE_ESTABLISHED = '01'
 # STATE_SYN_SENT = '02'
 # STATE_SYN_RECV = '03'
 # STATE_FIN_WAIT1 = '04'
 # STATE_FIN_WAIT2 = '05'
 # STATE_TIME_WAIT = '06'
 # STATE_CLOSE = '07'
 # STATE_CLOSE_WAIT = '08'
 # STATE_LAST_ACK = '09'
 STATE_LISTEN = '0A'
 # STATE_CLOSING = '0B'
 
 
 def get_socket_inodes(pid):
     '''
     Get list of socket inodes for process pid.
     '''
     base = '/proc/%i/fd' % pid
     inodes = []
     for item in os.listdir(base):
         target = os.readlink(os.path.join(base, item))
         if target.startswith('socket:'):
             inodes.append(int(target[8:-1]))
     return inodes
 
 
 def _remove_empty(array):
     return [x for x in array if x != '']
 
 
 def _convert_ip_port(array):
     host, port = array.split(':')
     # convert host from mangled-per-four-bytes form as used by kernel
     host = unhexlify(host)
     host_out = ''
     for x in range(0, len(host) // 4):
         (val,) = struct.unpack('=I', host[x * 4:(x + 1) * 4])
         host_out += '%08x' % val
 
     return host_out, int(port, 16)
 
 
 def netstat(typ='tcp'):
     '''
     Function to return a list with status of tcp connections at linux systems
     To get pid of all network process running on system, you must run this script
     as superuser
     '''
     with open('/proc/net/' + typ, 'r', encoding='utf8') as f:
         content = f.readlines()
         content.pop(0)
     result = []
     for line in content:
         # Split lines and remove empty spaces.
         line_array = _remove_empty(line.split(' '))
         tcp_id = line_array[0]
         l_addr = _convert_ip_port(line_array[1])
         r_addr = _convert_ip_port(line_array[2])
         state = line_array[3]
         # Need the inode to match with process pid.
         inode = int(line_array[9])
         nline = [tcp_id, l_addr, r_addr, state, inode]
         result.append(nline)
     return result
 
 
 def get_bind_addrs(pid):
     '''
     Get bind addresses as (host,port) tuples for process pid.
     '''
     inodes = get_socket_inodes(pid)
     bind_addrs = []
     for conn in netstat('tcp') + netstat('tcp6'):
         if conn[3] == STATE_LISTEN and conn[4] in inodes:
             bind_addrs.append(conn[1])
     return bind_addrs
 
 # from: http://code.activestate.com/recipes/439093/
 
 
 def all_interfaces():
     '''
     Return all interfaces that are up
     '''
     is_64bits = sys.maxsize > 2**32
     struct_size = 40 if is_64bits else 32
     s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
     max_possible = 8  # initial value
     while True:
         bytes = max_possible * struct_size
         names = array.array('B', b'\0' * bytes)
         outbytes = struct.unpack('iL', fcntl.ioctl(
             s.fileno(),
             0x8912,  # SIOCGIFCONF
             struct.pack('iL', bytes, names.buffer_info()[0])
         ))[0]
         if outbytes == bytes:
             max_possible *= 2
         else:
             break
-    namestr = names.tostring()
+    namestr = names.tobytes()
     return [(namestr[i:i + 16].split(b'\0', 1)[0],
              socket.inet_ntoa(namestr[i + 20:i + 24]))
             for i in range(0, outbytes, struct_size)]
 
 
 def addr_to_hex(addr):
     '''
     Convert string IPv4 or IPv6 address to binary address as returned by
     get_bind_addrs.
     Very naive implementation that certainly doesn't work for all IPv6 variants.
     '''
     if '.' in addr:  # IPv4
         addr = [int(x) for x in addr.split('.')]
     elif ':' in addr:  # IPv6
         sub = [[], []]  # prefix, suffix
         x = 0
         addr = addr.split(':')
         for i, comp in enumerate(addr):
             if comp == '':
                 # skip empty component at beginning or end
                 if i == 0 or i == (len(addr) - 1):
                     continue
                 x += 1  # :: skips to suffix
                 assert(x < 2)
             else:  # two bytes per component
                 val = int(comp, 16)
                 sub[x].append(val >> 8)
                 sub[x].append(val & 0xff)
         nullbytes = 16 - len(sub[0]) - len(sub[1])
         assert((x == 0 and nullbytes == 0) or (x == 1 and nullbytes > 0))
         addr = sub[0] + ([0] * nullbytes) + sub[1]
     else:
         raise ValueError('Could not parse address %s' % addr)
     return hexlify(bytearray(addr)).decode('ascii')
 
 
 def test_ipv6_local():
     '''
     Check for (local) IPv6 support.
     '''
     import socket
     # By using SOCK_DGRAM this will not actually make a connection, but it will
     # fail if there is no route to IPv6 localhost.
     have_ipv6 = True
     try:
         s = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
         s.connect(('::1', 0))
     except socket.error:
         have_ipv6 = False
     return have_ipv6