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Asked: 2026-06-11T22:08:30+00:00

I am trying to UDP broadcast from a Python program to two LabView programs.

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I am trying to UDP broadcast from a Python program to two LabView programs. I cannot seem to get the broadcast to send and I am not sure where my socket initialization is wrong, broadcasting seems simple enough?? As far as I can see, there is no data being received by the other PC’s. Also, I will need this program to receive data back from the other PC’s in the future. It seems like that shouldn’t complicate things but every step of the way has been complicated for me!

Background: I have zero software experience, this is just something I was assigned at work. Any help is appreciated. Code is below. Python 2.7.

from threading import Thread  
import time  
from socket import *  

cs = socket(AF_INET, SOCK_DGRAM)  
cs.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)  
cs.setsockopt(SOL_SOCKET, SO_BROADCAST, 1)  
cs.connect(('<broadcast>', 5455)) 


while 1:
    cmd = int(raw_input('send: '))
    if (cmd == 1):
        cs.send('1')
    time.sleep(1)
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1 Answer

  1. Editorial Team

    You do not need to connect() to a UDP socket, instead:

    cs.sendto(data, ('255.255.255.255', 5455))

    EDIT: This seems to work for me:

    from socket import *
cs = socket(AF_INET, SOCK_DGRAM)
cs.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
cs.setsockopt(SOL_SOCKET, SO_BROADCAST, 1)
cs.sendto('This is a test', ('255.255.255.255', 54545))

    On another machine I ran tcpdump:

    tcpdump -i eth1 port 54545 -XX
listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes

14:04:01.797259 IP 10.22.4.45.33749 > 255.255.255.255.54545: UDP, length 14
0x0000:  ffff ffff ffff f0de f1c4 8aa6 0800 4500  ..............E.
0x0010:  002a 0000 4000 4011 2c81 0a16 042d ffff  .*..@.@.,....-..
0x0020:  ffff 83d5 d511 0016 fe38 5468 6973 2069  .........8This.i
0x0030:  7320 6120 7465 7374 0000 0000            s.a.test....

    You can see the text in the payload. As well as the broadcast Ethernet and IP dst addrs.

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