看不到来自另一台设备的 UDP 多播消息

2022-01-22 00:00:00 python python-3.x multicast interface udp

问题描述

我有一台 Windows 机器，其中有两个脚本通过 UDP 多播(在同一台机器上)发送和接收消息.我有一个 C 和 Python3 实现.Python3 看起来像这样:

I have a Windows machine where I have two scripts that send and receive messages via UDP multicast (on the same machine). I have a C and Python3 implementation of this. The Python3 one looks like this:

发件人.py

import socket

MCAST_GRP = '239.1.1.1'
MCAST_PORT = 1234

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 2)
print("Sending")
sock.sendto(bytearray("str()", "utf-8"), (MCAST_GRP, MCAST_PORT))

data, address = sock.recvfrom(1024)
print('received %s bytes from %s' % (len(data), address))
print(data)

receiver.py

receiver.py

import socket
import struct
import sys

multicast_group = '239.1.1.1'
server_address = ('', 1234)

# Create the socket
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

# Bind to the server address
sock.bind(server_address)

# Tell the operating system to add the socket to the multicast group
# on all interfaces.
group = socket.inet_aton(multicast_group)
mreq = struct.pack('4sL', group, socket.INADDR_ANY)
sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)

# Receive/respond loop
while True:
    print('
waiting to receive message')
    data, address = sock.recvfrom(1024)

    print('received %s bytes from %s' % (len(data), address))
    print(data)

    print('sending acknowledgement to', address)
    sock.sendto(bytearray("ack", "utf-8"), address)

我有另一个物理设备连接到同一台机器，但我的程序无法从它接收任何消息.我可以看到 Wireshark 正在查看来自其他物理设备的消息，这些消息通过 eth0 接口到达相同的 IP 和端口.我知道我的脚本生成的流量在 VirtualBox Host-Only Network 上.我不确定这是否会导致我看不到来自外部设备的 UDP 多播消息.

I have another physical device hooked up to the same machine but I cannot receive any messages from it with my programs. I can see that Wireshark is seeing the messages from the other physical device, these messages are coming over the eth0 interface to the same IP and Port. I know that the traffic generated by my scripts is on the VirtualBox Host-Only Network. I am not sure if that could cause the issue of me not seeing the UDP multicast messages from the external device.

我也在 Linux 机器上测试过(最新的 kali 版本)，但也无法从外部设备接收到任何消息.

I have tested it on a Linux machine as well (latest kali version) but could not receive any messages from the external device as well.

如果我遗漏了一些信息，请告诉我.

If I am missing some information, please let me know.

编辑 1:

我的设置如下:我正在运行本机 Windows 10 机器.这台机器是一个连接的设备，它正在运行一些我不知道的操作系统.我只能从中发送和接收消息.我可以通过在我的 Windows 10 机器上的物理以太网端口发送以太网、TCP 和 IPv4 数据包，方法是指定我为此使用的软件来使用 eth0 和我在网络适配器设置中分配给该端口的已定义 IP(v4) 地址(192.168.1.100)

My setup is as follows: I am running a native Windows 10 machine. To this machine is a device connected that is running some OS I don't know. I am only able to send and receive messages from it. I can send Ethernet, TCP, and IPv4 packets over the physical ethernet port on my Windows 10 machine by specifying the software I am using for this to use eth0 and a defined IP(v4) address I assigned to that port in the network adapter settings (192.168.1.100)

脚本在也连接到设备的同一台 Windows 10 计算机上运行.他们在这个接口 VirtualBox Host-Only Network 上发送，但我不知道为什么.我没有配置这样的东西.我认为接口应该不是问题，因为这就是 UDP 多播的工作原理(我不确定，所以如果我弄错了，请告诉我！)

The scripts are running on the same Windows 10 machine that is also connected to the device. They are sending on this interface VirtualBox Host-Only Network but I don't know why. I did not configure anything like this. I assume that the interface should not be a problem because that is how UDP Multicast works (I am not sure of that so if I am mistaken please let me know!)

发件人的示例输出如下所示:

A sample output of the sender looks like this:

Sending
received 3 bytes from ('192.168.56.1', 3000)
b'ack'

Process finished with exit code 0

和接收者:

waiting to receive message
received 5 bytes from ('192.168.56.1', 55132)
b'robot'
sending acknowledgement to ('192.168.56.1', 55132)

waiting to receive message

我希望澄清设置.如果仍有信息缺失，请告诉我！

I hope that clarifies the setup. If there is still information missing please let me know!

解决方案

如 https://www.tldp.org/HOWTO/Multicast-HOWTO-6.html，套接字 API 要求您识别接口以及要使用的多播地址/端口.

As covered in https://www.tldp.org/HOWTO/Multicast-HOWTO-6.html, the sockets API requires that you identify the interface as well as the multicast address/port you want to use.

通过在示例代码中未指定此内容，您已将其留给操作系统来选择，并且它选择了 VirtualBox Host-Only 网络.不幸的是，这种类型的网络仅限于在 Windows 机器上运行的虚拟机.

By not specifying this in your sample code, you have left this down to the OS to pick and it has picked a VirtualBox Host-Only Network. Unfortunately this type of network is limited to VMs running on the Windows machines.

要修复它，您需要确定要用于多播的接口，并将其传递给您的发送和接收代码.例如:

To fix it, you need to identify the interface that you want to use for the multicast and pass that in to your sending and receving code. For example:

sock.setsockopt(socket.SOL_IP, socket.IP_MULTICAST_IF, socket.inet_aton(MCAST_IF_IP))

接收器.py

mreq = struct.pack('4s4s', group, socket.inet_aton(MCAST_IF_IP))

其中 MCAST_IF_IP 是您要使用的接口的 IP 地址.

where MCAST_IF_IP is the IP address of the interface that you want to use.

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