如何更改套接字的IP_MULTICAST_IF

Question

我有一台电脑，有5个接口:3个带公网I，2个本地I。我正在尝试向UDP服务器发送"HELLO“，但我想将接口更改为本地IP地址之一。我做了一些研究，这是我需要在python中添加的代码行：

sock.setsockopt(socket.SOL_IP, socket.IP_MULTICAST_IF, socket.inet_aton("64.195.10.11"))

其中64.195.10.11是我想要更改的IP

所以我的python代码看起来像这样：

import socket

MCAST_GRP = '224.0.0.1'
MCAST_PORT = 10222

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
sock.setsockopt(socket.SOL_IP, socket.IP_MULTICAST_IF, socket.inet_aton("64.195.10.10"))
sock.sendto("HELLO", (MCAST_GRP, MCAST_PORT))

当我在我的3个公共IP地址之间切换时，它工作得很好。但是，如果我在参数中放入本地IP，它就不起作用(数据包不会被传送)。我不确定是脚本没有发送，还是服务器没有接收。这是怎么回事？

服务级别

编辑:我正在用两种方式收听：

import socket
import sys

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.bind(("", 10222))
sock.setsockopt(socket.IPPROTO_IP,
                                 socket.IP_ADD_MEMBERSHIP,
                                 socket.inet_aton("224.0.0.1") +
                                 socket.inet_aton("64.195.10.11"))
sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_LOOP, 0)

while True:
    print >>sys.stderr, '\nwaiting to receive message'
    data, address = sock.recvfrom(1024)

    print >>sys.stderr, 'received %s bytes from %s' % (len(data), address)
    print >>sys.stderr, data

    print >>sys.stderr, 'sending acknowledgement to', address
    sock.sendto('ack', address)

并使用twisted：

from twisted.internet.protocol import DatagramProtocol
from twisted.internet import reactor
from twisted.application.internet import MulticastServer

class MulticastServerUDP(DatagramProtocol):
    def __init__ (self, group, name):
        self.group = group
        self.name = name
    def startProtocol(self):
        print '%s Started Listening' % self.group
        self.transport.joinGroup(self.group)

    def datagramReceived(self, datagram, address):
        print "%s Received:"%self.name + repr(datagram) + repr(address)

reactor.listenMulticast(10222, MulticastServerUDP('224.0.0.1', 'SERVER1'), listenMultiple = True)             
reactor.run()

Answer 1

答案是:我防火墙不接受来自RFC1918 IP地址的udp数据包。

Answer 2

如果服务器和客户端在同一台机器上(为了测试)，您可能需要像这样设置IP_MULTICAST_LOOP选项(c代码)：

int loop_on = 1;
setsockopt(socket, IPPROTO_IP, IP_MULTICAST_LOOP, &loop_on, sizeof(loop_on));

在python中，您可以尝试如下所示：

sock.setsockopt(socket.SOL_IP, socket.IP_MULTICAST_LOOP, 1)

希望这能有所帮助。

编辑:添加一些跟踪(来自我的Linux机器)

我使用的代码与SquallLeohart发布的代码相同：

#! /usr/bin/python

import socket

MCAST_GRP = '224.0.0.1'
MCAST_PORT = 10222

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
sock.setsockopt(socket.SOL_IP, socket.IP_MULTICAST_IF, socket.inet_aton("192.168.1.7"))
sock.sendto("HELLO", (MCAST_GRP, MCAST_PORT))

和：

#! /usr/bin/python
import socket
import sys

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.bind(("", 10222))
sock.setsockopt(socket.IPPROTO_IP,
                                 socket.IP_ADD_MEMBERSHIP,
                                 socket.inet_aton("224.0.0.1") +
                                 socket.inet_aton("192.168.1.7"))
sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_LOOP, 0)

while True:
    print >>sys.stderr, '\nwaiting to receive message'
    data, address = sock.recvfrom(1024)

    print >>sys.stderr, 'received %s bytes from %s' % (len(data), address)
    print >>sys.stderr, data

    print >>sys.stderr, 'sending acknowledgement to', address
    sock.sendto('ack', address)

我得到了以下输出：

waiting to receive message
received 5 bytes from ('192.168.1.7', 43761)
HELLO
sending acknowledgement to ('192.168.1.7', 43761)

waiting to receive message
received 5 bytes from ('192.168.1.7', 52326)
HELLO
sending acknowledgement to ('192.168.1.7', 52326)

waiting to receive message

使用tcpdump：

21:01:33.814728 IP localhost.localdomain.34956 > all-systems.mcast.net.10222: UDP, length 5
21:01:35.364605 IP localhost.localdomain.39078 > all-systems.mcast.net.10222: UDP, length 5
21:01:36.228477 IP localhost.localdomain.49926 > all-systems.mcast.net.10222: UDP, length 5

致以问候。