UDP Socket is not receiving any message with python

Question

I am trying to send message from Raspberry Pi (Ubuntu 20) to Laptop (Virtualbox Ubuntu 20) via UDP socket. So I am using simple code from https://wiki.python.org/moin/UdpCommunication

Sending (from Raspberry Pi)

import socket

UDP_IP = "127.0.0.1"
UDP_PORT = 5005
MESSAGE = b"Hello, World!"

print("UDP target IP: %s" % UDP_IP)
print("UDP target port: %s" % UDP_PORT)
print("message: %s" % MESSAGE)

sock = socket.socket(socket.AF_INET, # Internet
                     socket.SOCK_DGRAM) # UDP
sock.sendto(MESSAGE, (UDP_IP, UDP_PORT))

Receiving (from laptop)

import socket

UDP_IP = "127.0.0.1"
UDP_PORT = 5005

sock = socket.socket(socket.AF_INET, # Internet
                     socket.SOCK_DGRAM) # UDP
sock.bind((UDP_IP, UDP_PORT))

while True:
    data, addr = sock.recvfrom(1024) # buffer size is 1024 bytes
    print("received message: %s" % data)

I tried UDP_IP = "0.0.0.0" in both ends. I tried Ip address of my laptop at RPI end. I tried both machine's IP address at both ends. I tried sock.bind(("", UDP_PORT)) to bind all. I tried adding the UDP port number in firewall settings. I checked multiple questions from this forum related to this.

Still, I cannot get any packets at the laptop receiving side. I do not know what is wrong. Please advise.

1. You are binding the receiving socket to 127.0.0.1. That means it can't receive datagrams from anywhere but the localhost. 2. You are sending to 127.0.0.1, which again means the localhost, not a remote host. Fix these. Bind to 0.0.0., and send to the real IP address of the target. — user207421

Mateo Lara Mateo Lara · Accepted Answer · 2020-07-30T23:15:06

The problem may be in the IP address because you are using the IP '127.0.0.1' (localhost) to reach an outside device. Please find out the IPs of your devices, try using ifconfig Linux command. Also, check that nothing is blocking your connection.

Consider that for socket.bind(address) you can use '0.0.0.0' and for socket.sendto(bytes, address) you should use the IP of the device you want to send to.

I recommend you to download a program called Hercules, with this program you can create a UDP peer to figure out what is not working properly. For example, you could use python in one side and Hercules in the other to rule out mistakes in one side of the code execution, you could also try two Hercules connections and see if you can establish communication in which case the problem is most likely related to the code execution, in the other hand if you can not establish a connection between the two Hercules UDP peers the problem is most likely with the devices or the network itself.

UDP Socket is not receiving any message with python

3 Answers