Python UDP broadcast

Question

Ok im going to try an explain what is going on here... I have a network of multiple same type devices. I have a program that runs on any pc on the network that discovers these individual devices and categorizes them by ip, name, mac, etc.. This program allows for configuration of each device. The devices broadcast a udp packet to "255.255.255.255" with the information for discovery. I can run wireshark and intercept the packets broadcasted from the devices. I have a python program that will broadcast udp packets with data of my choosing.. Now.. This stems from me learning python and my project oriented approach.. I learn better this way :). Ok that being said.. My idea is to broadcast the exact udp packet that another device broadcasts, which in turn should land me on the discovery software as a particular network device.. By following udp stream in wireshark i can copy the data and enter it in my python program and broadcast it on the network. I can broadcast to any destination ip and see it in wireshark but when i try and send it to 255.255.255.255 it never shows up. Now i understand that routers will not forward 255x4 broadcasts pass the local network. When i run the discovery program i can see all the devices broacasting their packets to 255x4 but not the packet originating from my pc. Any ideas would be greatly appreciated.

Python Code:

import udp
import socket   #for sockets
import sys  #for exit

# create dgram udp socket
try:
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
except socket.error:
    print 'Failed to create socket'
    sys.exit()

host = '255.255.255.255';
port = 55558;

while(1) :
    msg = '''...z..
hrQT.b.......hrQT.b
.....w...NanoStation M2...N2N
..Test......"XM.ar7240.v5.6.2.27929.150716.1201........NanoStation M2'''
    try :
        #Set the whole string
        s.sendto(msg, (host, port))

        # receive data from client (data, addr)
        d = s.recvfrom(1024)
        reply = d[0]
        addr = d[1]

        print 'Server reply : ' + reply

    except socket.error, msg:
        print 'Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
        sys.exit()

You probably want to use multicast so that you only interrupt the interested devices, not every device on the network. Using broadcast is a bad idea. So bad that broadcast was completely removed from IPv6 in favor of multicast. Many companies will reject applications that use broadcast because it interrupts every host on the LAN for no good reason, and it presents something of a security risk. — Ron Maupin

Bruno Rijsman Bruno Rijsman · Accepted Answer · 2019-01-08T14:43:19

To receive UDP packets, you need to bind the socket to the IP address and UDP port that you want to receive packets on.

   1 import socket
   2 
   3 UDP_IP = "127.0.0.1"
   4 UDP_PORT = 5005
   5 
   6 sock = socket.socket(socket.AF_INET, # Internet
   7                      socket.SOCK_DGRAM) # UDP
   8 sock.bind((UDP_IP, UDP_PORT))
   9 
  10 while True:
  11     data, addr = sock.recvfrom(1024) # buffer size is 1024 bytes
  12     print "received message:", data

I would recommend using different UDP sockets for sending and receiving packets.

Python UDP broadcast

1 Answers