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PORead from UDP multicast raspberry pi
 

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  1. PORead from UDP multicast raspberry pi
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    <p>I've already started a question here (<a href="https://stackoverflow.com/questions/15671961/getting-local-udp-server-information-into-c"><strong>link</strong></a>) about this project I'm doing, and I keep having lots of problems with this. </p> <p>In my earlier question I wanted to read from a same machine udp multicast and I find out how to do it, but not with ipmidi.(If you didn't read the previous question linked above, ipmidi is a tool for mac/win which allows me to send midi events through an UDP multicast).</p> <p>I've been working around with wireshark and managed to see that ipmidi is sending datagrams to the ip 225.0.0.37, port 21928, wich tells me that is, in fact, a multicast. Then I used <a href="http://ntrg.cs.tcd.ie/undergrad/4ba2/multicast/antony/example.html" rel="nofollow noreferrer"><strong>this</strong></a> code (the listener) to try to echo the datagrams sent by ipmidi with no success (I changed the multicast ip and the port). After this I decided to try to run this code from the raspberry pi, since I only wanted it to run in my mac for testing purposes, I went to the real thing. </p> <p>In my raspi I compiled the code again and gcc claimed that <code>setsockopt()</code> had an invalid argument. <code>perror()</code> was useful enough to tell me that the problem was here:</p> <pre><code>setsockopt(fd,IPPROTO_IP,IP_ADD_MEMBERSHIP,&amp;mreq,sizeof(mreq)) </code></pre> <p>So I removed the part where it asks for a multicast address to the kernel and made it a simple listening socket at port 21928, but it still won't work. I have my mac sending midi through ethernet to the raspi. </p> <p>Now, the actual questions:</p> <ol> <li><p>I'm now doubting my multicast, so called, knowledge: if my mac is multicasting ipmidi's datagrams, it means the datagrams are being sended through all the possible places in my mac, right? I mean, the ip 225.0.0.37 means multicast through wifi and ethernet or I have to route it to the network interface of my choice?</p></li> <li><p>Since my raspi is, allegedly, receiving the datagrams through the ethernet, making my program listen at the ipmidi's datagram destination port would be enough or do I have to tell it explicitly 'where' those datagrams came from?</p></li> <li><p>Is there an easier way to make a multicast receiving app, like an api for C/C++? I'm currently using C style sockets, as you could see in the code I linked, but this is not the main purpose for the program I'm doing and I find myself spending lots of time just learning about networking instead of focusing on the real thing. </p></li> </ol> <p>Sorry for the long question, lots of doubts and I wanted to be in context. </p> <p>Thanks for the help!</p>
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