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copied!<p>You can use <code>connect()</code> to 127.0.0.1 on the multicast socket, then the IP stack can filter for you.</p> <p><strong>Updated with source code to demonstrate</strong></p> <p>You can run this script multiple times on one host and see the multicast packets distributed:</p> <pre><code>#!/usr/bin/python import platform, time, socket, select addr = ("239.255.2.9", 1600) sendSock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP) sendSock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 24) sendSock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_IF, socket.inet_aton("127.0.0.1")) recvSock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP) recvSock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, True) if hasattr(socket, 'SO_REUSEPORT'): recvSock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, True) recvSock.bind(("0.0.0.0", addr[1])) status = recvSock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, socket.inet_aton(addr[0]) + socket.inet_aton("127.0.0.1")); sendSock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, True) if hasattr(socket, 'SO_REUSEPORT'): sendSock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, True) sendSock.bind(("127.0.0.1", addr[1])); recvSock.connect(("127.0.0.1", addr[1])); while 1: pkt = "Hello host: {1} time: {0}".format(time.ctime(), platform.node()) print "SEND to: {0} data: {1}".format(addr, pkt) r = sendSock.sendto(pkt, addr) while select.select([recvSock], [], [], 0)[0]: data, fromAddr = recvSock.recvfrom(1024) print "RECV from: {0} data: {1}".format(fromAddr, data) time.sleep(2) </code></pre> <p>To initiate packets from a different interface:</p> <pre><code>#!/usr/bin/python import platform, time, socket, select sendSock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP) pkt = "Hello from network."; sendSock.sendto(pkt, ('10.65.42.129', 1600)) </code></pre> <p>I ran all three on Cygwin on Windows XP and verified the result to be as required.</p> <p><strong>Example output</strong></p> <pre><code>SEND to: ('239.255.2.9', 1600) data: Hello host: NYCMDV8X5R1 time: Thu Feb 21 13:15:15 2013 RECV from: ('127.0.0.1', 1600) data: Hello host: NYCMDV8X5R1 time: Thu Feb 21 13:15:14 2013 RECV from: ('127.0.0.1', 1600) data: Hello host: NYCMDV8X5R1 time: Thu Feb 21 13:15:15 2013 SEND to: ('239.255.2.9', 1600) data: Hello host: NYCMDV8X5R1 time: Thu Feb 21 13:15:17 2013 RECV from: ('127.0.0.1', 1600) data: Hello host: NYCMDV8X5R1 time: Thu Feb 21 13:15:16 2013 RECV from: ('127.0.0.1', 1600) data: Hello host: NYCMDV8X5R1 time: Thu Feb 21 13:15:17 2013 </code></pre> <p>Previously the output would show external packets, for example:</p> <pre><code>SEND to: ('239.255.2.9', 1600) data: Hello host: NYCMDV8X5R1 time: Thu Feb 21 13:07:05 2013 RECV from: ('10.65.42.129', 4711) data: Hello from network. RECV from: ('127.0.0.1', 4710) data: Hello host: NYCMDV8X5R1 time: Thu Feb 21 13:07:05 2013 SEND to: ('239.255.2.9', 1600) data: Hello host: NYCMDV8X5R1 time: Thu Feb 21 13:07:11 2013 RECV from: ('10.65.42.129', 4712) data: Hello from network. </code></pre>

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